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EyeLink System Documentation

1. EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 64 4 4 2 3 GAZE Gaze position data reports the actual x y coordinates of the subject s gaze on the display compensating for head position changes and distance from the display The units are in actual display coordinates usually pixels which can be set in the EyeLink II configuration file PHYSICAL INI These are the most useful coordinates for most applications but may not reflect true eye rotation velocities due to head movements The default EyeLink II coordinates are those of a 640 by 480 VGA display with 0 O at the top left The resolution data for gaze position data changes constantly depending on subject head position and point of gaze and therefore is reported as a separate data type see below A typical resolution is 22 pixels per degree for the suggested EyeLink II setup with the distance between the subject s eyes and the display being twice the display s width and with the standard 640 by 480 screen resolution The high resolution of the EyeLink II data is preserved by multiplying the position by a prescaler recording the value as an integer in the EDF file then dividing by the prescaler when the file is read The usual prescaler value is 10 allowing gaze position to be recorded with 0 1 pixel of resolution or a resolution of 0 0045 degree Actual EyeLink II resolution is limited only by measurement noise which is less than 2 units RM
2. For long term storage shipping or transportation it is recommended that the EyeLink II headband and marker cable be stored in the shipping case that you originally received the system in Printed instructions are attached under the foam insert in the lid of the case and are duplicated here Store the shipping case above freezing and below 40 C and avoid high humidity conditions which might cause water to condense within the headband and damage the optics Be sure to follow the unpacking and installation instructions when returning the packaged unit to operation To pack the headband l 2 9 8 9 Tighten the height adjustment and rear clamps as far as possible Loosen the upper clamps and slide the camera arms up as far as possible Tilt the arms up so the cameras are nearly parallel to the headband frame and point the cameras down To prevent scratching of the arms and head camera place the cardboard spacers between the arms and the head camera then fold the arms up against the head camera Place the camera lens caps on the eye cameras Place the supplied bubble wrap around the eye cameras and between the eye cameras and the head camera Place the headband into the foam cutout with the cable through the back of the cutout Place the foam bag over the connector end of the headband cable Feed the headband cable into the foam cutout making a figure eight pattern to avoid twisting the cable 10 Use the wir
3. The EyeLink II Host PC performs real time eye tracking at 250 or 500 samples per second while also computing true gaze position on the subject display On line detection analysis of eye motion events such as saccades and fixations is also performed This data can be stored in a data file on the Host PC sent through the Ethernet link to the Display PC or output as analog signals if the analog digital I O card is installed From the Host PC the operator performs subject setup monitors performance and can control applications running on the Display PC The Host PC has these key attributes e Hosts EyeLink II high speed eye tracking card optional analog output digital input card e Runs a special operating system to host the EyeLink II operator software Your original operating system such as Windows XP is still available if disk the partitioning utility included with self installation kit is used during installation e Functions either as standalone tracker or connected to display computer through 1OBASE T Ethernet cable e In standalone configuration data output is to hard disk or through optional analog output card e Response box or game pad connected by a USB port e Keyboard display and pointing device are used to control tracker or as remote keyboard for applications on display computer e EyeLink II software integrates all needed eye tracking functionality including subject setup calibration real time data throu
4. go to Offline screen Select Output Record to go to the output screen from which you can start a manual recording session This Output Record button is usually only access when using the EyeLink II in standalone mode Keys O go to Output screen Select Set Options to go to the EyeLink II options screen where a variety of system options and settings can be configured Note that any value on this screen can be programmatically overridden by the API during experiment setup Keys S go to Set options Press Help F1 to access the online help page for Camera Setup All available key shortcuts are also listed on the Help screen Keys F1 open Help screen Select Calibration to go to the Calibration Calibration screen After setting up the eye cameras and thresholding you need to Calibrate the system EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 14 Select Validation to be taken to the Validation Screen Validation allows you to get a sense of the gaze position Validation accuracy of your Calibration Validation should always be run after Calibration Keys V go to Validate screen Select Drift Correction to go to the Drift Correction Screen Drift Correction can be performed before and during an experiment allowing gaze position to be realigned if headband slippage or significant pupil size change has increased gaze calculation error Keys D go to Drift
5. the saccade lt sxp gt lt syp gt lt exp gt lt eyp gt are listed The total visual angle covered in the saccade is reported by lt ampl gt which can be divided by lt dur gt 1000 to obtain the average velocity Peak velocity is given by pv Optionally the eye position angular resolution in units per visual degree are given as well All samples that are within the saccade will be listed between the SSACC and ESACC events for each eye simplifying data analysis 4 9 3 6 Blinks e SBLINK lt eye gt lt stime gt e EBLINK lt eye gt lt stime gt lt etime gt lt dur gt Blinks periods of data where the pupil is missing are reported by the SBLINK and EBLINK lines The time of the start of the blink is indicated by the SBLINK line which can be eliminated with the EDF2ASC nse option The lt eye gt is L or R indicating the eye s data that produced the event The end and duration are given in the EBLINK event Blinks are always embedded in saccades caused by artifactual motion as the eyelids progressively occlude the pupil of the eye Such artifacts are best eliminated by labeling and SSACC ESACC pair with one or more SBLINK events between them as a blink not a saccade The data contained in the ESACC event will be inaccurate in this case but the lt stime gt lt etime gt and lt dur gt data will be accurate It is also useful to eliminate any short less than 120 millisecond duration fixations t
6. A Auto Trigger Press to accept calibration fixation Accept Only works after calibration dot Fixation sequence has finished Keys ENTER Accept Fixation Auto Trigger 2 3 4 3 Key Shortcuts Fl Help screen Camera setup Auto calibration set to the pacing selected in Set Options menu Auto trigger ON EyeLink accepts current fixation if it is stable During Calibration ENTER Begins calibration sequence or accepts calibration value oiven Terminates calibration sequence Manual calibration Auto trigger turned off if it is stable After Calibration Fi Help screen Visi Validate calibration values o o oZ o o o o ESC Discard calibration values Auto calibration set to the pacing selected in Set Options menu Auto trigger ON EyeLink accepts current fixation Fl ESC A ESC M A Fl V ESC EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 22 2 3 5 Validation Screen Validate ICPA IP Link Open Status Panel Sequence Options 1 Hate a Fixation Tracking Binocular Pupil HEAD Validation 1H points Point 1 of 16 TU TRACKING i it Validation sequence M i point Camera view with threshold status Figure 2 6 EyeLinkll Validation Screen 2 3 5 1 Purpose The Validate screen displays target positions to the participant and measures the difference between
7. D Loads default configuration 2 3 3 3 Key Shortcuts EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 19 P_ Pacing Delay For auto sequence 10 0 0 o O R Randomize calibration order O Z O Z o O 1 Repeat first point of calibration O Z O Z O o M_ JMousesimultionofeye O Z o Z S O E Eye event data to saccade detector 1 10 0 X Saccade detector sensitivity O o O Z o Z F File data contents selection PE Raw eye position in samples 4 HREF eye position in samples G Gaze position and resolution in samples o B Button flags in samples _ S O Return to previous screen HELP screen L Revert to configuration from last session This is still saved even when the PC is turned off Hcc Load default configuration Default ini EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 20 2 3 4 Calibration Screen Calibrate TCP IP Link Open ee nk LISA ATARI AG AISSCHG H 231 ha Status Panel Sequence Options Tracking Binocular Pupil STABLE HEAD Calibration 9 point grid Point 1 of 10 TRACKING Calibration sequence OFF point Camera view with threshold status Figure 2 5 EyeLink II Calibration Screen 2 3 4 1 Purpose Calibration is used to collect fixations on target points in order to map raw eye data to either gaze position or
8. EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 6 NOTE This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at the users expense WARNING Changes or modifications not expressly approved by SR Research Ltd could void the user s warranty and authority to operate the equipment EyeLink I User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 7 2 EyeLink Il Tracker Application Operation 2 1 Starting the Host Tracker To start the EyeLink II Host Tracker follow these simple steps a Start your Host PC b If your system was installed with BootMagic select the EyeLinkII partition c If the EyeLink II Tracker program does not automatically start type the following at the command prompt cd eyelink2 exe ENTER eyelink2 exe ENTER The EyeLink II Tracker application should start and display the Offline t
9. HREF data Targets are presented for the participant to fixate on the Display PC while feedback graphics are presented to the experimenter on this display The calibration is automatically checked when finished and diagnostics given Calibration should be performed after camera setup and before Validation The two camera images along with threshold values are at the bottom left of the screen The eyes to be calibrated as well as the calibration type as defined in the Set Options screen or via the EyeLink API are indicated beside the camera images at the bottom of the screen The calibration status and current calibration point being presented are indicated on the bottom right of the screen EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 21 To perform a calibration have the participant look at the first fixation point and press the Accept Fixation button or the ENTER or Spacebar key to start the validation If auto trigger is not enabled repeat this action after each target fixation 2 3 4 2 Main Functions Press to go to the camera setup Camera Setup ee Keys ENTER Camera Setup Press to see the help menu which Help F1 contains a description of the role of this screen and the keys for functions Keys F1 Help screen Terminate Calibration sequence hort Keys ESC Abort Press to have a automated calibration sequence Sequence pacing selected in the setup options menu Keys
10. I User Manual 07 02 2000 2002 2006 SR Research Ltd 4 oo Digital Inputs arid OutDUtsuionsseso dioec oet ub Rene 97 8 3 1 Analog Data Output Assignments sessi ease nennen nnn nnns 98 8 3 2 Analog Data Types and Ranges sisse seen nnns 99 O9 Scaling OF Analog Fosilon Dalai NAN 99 8 4 dPupilsize DAt3ssese istas E PH eiu ads attirer 100 8 5 Time base and Data Strobe ss 100 0 9 1 SOLE DATA DD uesssosamadet estera ed Eod balneo E sh prox pu REM ie ten 101 8 5 2 Over sampling and Toggle Strobe sees nnns 101 EyeLink I User Manual 07 02 2000 2002 2006 SR Research Ltd List of Figures Figure 1 1 Typical EyeLink II System Configuration eese 2 Figure 2 1 Screen Overview of EyeLink II Tracker Program 9 Figure 2 2 EVeEINKRII OEME SET annee meuaenic EUM 10 Figure 2 3 EyeLink Il Camera Setup Screen vs ss ccssecescssavsederaveasesetatserceseraveadiies 12 Figure 2 4 EyeLinkII Set Option Screen ss 16 Figure 2 5 EyeLink II Calibration Screen 21 Fig re 2 6 EyeLinkil Validation Cree i icin none sn etant 29 Figure 2 7 EyeLinkil Drift Correction Screen eo eee ee urea aee EP RUE EE 25 Figure 2 8 EbyeLlinkll Output SOcteenc oce eot HERRERA RUE nantes 27 Figure 2 9 byeLlinkll RECOrdsSCreen zs oodd o EI dodi nee 29 Fig re 2 10 Byelink H Stat s Pane eoi topi in ini ot orte puPS 31 Figure 3 1 Example Cam
11. SR Research Ltd 65 4 4 3 Pupil Size Data Pupil size is also measured by the EyeLink II system at up to 500 samples per second It may be reported as pupil area or pupil diameter The pupil size data is not calibrated and the units of pupil measurement will vary with subject setup Pupil size is an integer number in arbitrary units Typical pupil area is 800 to 2000 units with a precision of 1 unit while pupil diameter is in the range of 1800 3000 units Both measurements are noise limited with noise levels of 2 10 units RMS This corresponds to a resolution of 0 015 mm fora 5 mm pupil Pupil size measurements are affected by up to 10 by pupil position due to the optical distortion of the cornea of the eye and camera related factors If research using pupil size is to be performed the subject should not move their eyes during the trails They can be presented with a fixation point with aural stimulus presentation or a single stimulus position at display center may be used It is also possible to counterbalance stimulus position during the experiment 4 4 4 Button Data The state of up to 8 buttons or input port bits may be recorded in each sample Button ports bits and polarity may be set in the EyeLink II tracker configuration file BUTTONS INI The button data consists of two 8 bit fields recorded as a 16 bit number The lower 8 bits contain the current status of the 8 buttons bit O if off 1 if pressed Each of the uppe
12. User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 43 The proper timing is best learned by watching the gaze cursor during validation discussed later The EyeLink II system helps prevent improper triggering by locking out the 4 key if the eye is moving Sometimes the J key will be locked out because of poor eye camera setup with the pupil noisy or undetected in some positions You can use the lt or gt keys on the operator keyboard to select the eye camera image to view on screen and the f and U keys to change the threshold if required If this fails or the eye camera needs repositioning press the ESC key to exit back to the Camera Setup menu After the first fixation has been accepted several more calibration targets are displayed in sequence and fixations for collected each The EyeLink II calibration system presents these targets in a random order which discourages subjects from making saccades away from the current target before it disappears If automatic sequencing has been enabled targets will be presented and fixations collected without further intervention Each time a new target is displayed the subject quickly makes a saccade to it The EyeLink II system detects these saccades and the fixation following producing an automated sequencing system NOTE Sequencing may halt if the setup of one or both eyes causes pupil loss or noise at the target position If this happens adjust the threshold and re
13. away from the face twisting the rod though the rod clamp This may cause the eye image to tilt as well which is not a problem This may require some practice try setting up the headband on yourself while watching the display on the operator monitor EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 39 Poor Focus Good Focus Figure 3 4 Focusing the Eye Camera The eye camera should be focused by rotating the lens holder Figure 13 The best focus will minimize the size of the two eye illuminator corneal reflections which can be seen below the pupil and to each side Turn the lens by placing your thumb on the bottom of the camera and turning the lens holder by sliding your index finger along the top of the camera This will keep your fingers away from the subject s eyes and prevent the camera image from being blocked The focus may also change the size of the eye image which may require the eye camera distance to be reset 3 3 Setting Pupil Threshold The camera image of the eye should now be clear with the pupil centred when the subject looks at the eye image on the subject computer s display The pupil threshold may now be automatically set by pressing the Auto Threshold button or the A key when the eye camera image is selected The pupil of the eye should be solidly blue with no other colour in the image when the thresholding is properly set If large areas are colored the subject may ha
14. but may eliminate some 1 saccades as well The threshold should be set to zero for non cognitive research or where statistics such as saccadic duration amplitude and average velocity are required Examples of the commands to set these thresholds are saccade_velocity_threshold 30 saccade acceleration threshold 8000 saccade motion threshold 0 15 4 3 6 Pursuit Thresholds During smooth pursuit and nystagmus saccades must be detected against a background of smooth eye motion as fast as 70 sec While acceleration can be used to detect these saccades velocity data must also be used for reliable detection of all saccades The EyeLink II parser raises the saccadic velocity threshold during pursuit by the average velocity over the last 40 milliseconds This is reliable and does not degrade parser performance during non pursuit eye movements During long saccades such as the return sweep in reading this fix up causes the saccadic velocity threshold to be raised This is not a problem as long as the adjustment is limited as it helps to prevent prolongation of these saccades by overshoots and glissades The pursuit threshold limits the amount that the saccadic threshold can be raised A limit of 60 sec works well for most pursuit and other research but may have to be raised if very rapid pursuit or nystagmus is being recorded The limit is set in degrees per second An example of this command is saccade_pursuit_fixup 60 4 3
15. consequential or incidental damages the above limitation may not apply to you 7 4 Copyrights Trademarks EyeLink is a registered trademark of SR Research Ltd All other company and or product names are trademarks of their respective manufacturers Product design and specifications may change at any time without notice EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 95 8 Appendix A Using the EyeLink II Analog and Digital Output Card The EyeLink II eye tracking system supports analog output and digital inputs and outputs via a DT334 card The analog card supplies up to 8 channels of 16 bit resolution analog output and 16 bits each of digital input and output The analog outputs may be used to output up to 6 channels of eye and gaze position data for use by non link and legacy applications Digital inputs may be defined as buttons used for controlling the EyeLink tracker or recorded to the EDF data file The outputs may be controlled by out port commands via the link or used by the EyeLink tracker for data strobes and other functions A digital only card the DT335 is also available This appendix describes how to configure and use the EyeLink II analog and digital outputs While some ideas for input and control of the tracker will be introduced applications are not limited to those introduced here In addition other digital input and output ports may be used including the game ports and the print
16. consists of two 8 bit fields recorded as a 16 bit number The lower 8 bits contain the current status of the 8 buttons bit O if off 1 if pressed Each of the upper 8 bits will be set to 1 if its button has changed since the last sample The least significant bit in each byte corresponds to button 1 and the most significant is button 8 Button events are usually recorded at the start of each recording block with all upper 8 bits change flags set to O This allows applications to track the current button state at all times 4 5 3 Eye Movement Events Events are generated by the EyeLink II tracker in real time from the eye movement data stream These provide an efficient record of the data in a form EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 67 ready to use for most types of eye movement research The use of events simplifies the analysis of sample data as well For example analysis of pursuit gain requires rejection of saccades which are clearly marked in the events Eye movement events are generated in pairs one event at the start of an eye movement condition and another at the end of the condition When used in real time processing with data set via the link the event pairs allow an application to monitor eye movement state in real time These pairs accurately label the samples in a file between the events as the file is read from beginning to end Eye movement events are always labeled b
17. display is drawn by the TRACK EXE application in response to commands from the EyeLink II system The Host PC display will also display the raw pupil position as a moving colored circle anda thresholded eye camera image A status bar at the bottom right of the display reports the progress of the calibration The pupil position cursor s will jump about when the subject looks about on the display and becomes still when properly fixating the calibration target Instructing the subject to carefully look at the white spot in the middle of the black calibration target will help improve fixation stability Head movements during calibration should be discouraged small head movements are corrected but large movements will severely degrade calibration accuracy due to distortion of the calibration data pattern and range If the cursor jumps continuously and rapidly or disappears intermittently the setup for one or both eye has problems The eye movement condition is also visible at the right side of the status bar at the bottom of the operator s display When the pupil appears stable to accept the first fixation press the Accept Fixation button or the J ENTER key or spacebar keys The pupil tends to come to rest gradually and to make small vergence movements at the start of the fixation so do not respond too quickly However do not wait too long before accepting the fixation as subjects soon begin to make involuntary saccades EyeLink Il
18. example short fixations may need to be discarded or merges with adjacent fixations or artifacts around blinks may have to be eliminated Nonetheless the EyeLink II parser does an excellent job in most recording situations Adjusting the configuration of the parser may help to bias its performance for specific applications such as smooth pursuit or reading research Its performance is easily checked record eye movements using the display of interest with both sample and event data Then view the file with EyeLink Data Viewer to see the correspondence between eye movements and the parser output 4 3 3 EyeLink Parser Configuration The saccadic detection parameters for the EyeLink II on line parser may need to be optimized for the type of experimental investigation being performed For example neuro psychophysical researchers may need to detect small saccades amid pursuit or nystagmus while reading researchers will need to detect only large saccades and will want fixation durations maximized This section EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 58 explains the function of and suggests values for the most useful parser parameters Some experimentation may be required to select the best parameters If an EDF file has been recorded with full sample data it can be reprocessed by the EyeLink II tracker allowing the parser configuration in PARSER INI to be fine tuned The eye movement data can then be
19. feedback displays by sending drawing commands to EyeLink II before recording begins TRACK displays the gaze position as a red cursor on the subject display The cursor can be toggled on and off by the G key on the Display PC keyboard To implement this feedback TRACK requests that EyeLink send it 250 or 500 samples per second of gaze position via the EyeLink II Windows DLL This data is used to move the gaze cursor TRACK also sends commands to the Host PC to create a data file DATA EDF on the Host PC s hard disk which contains samples fixations and saccade data When the TRACK exits this file will be automatically transferred from the Host PC to the Display PC DATA EDF may be viewed with EyeLink Data Viewer see the EyeLink Data Viewer User s Manual for information on this optional data analysis tool or processed with other EDF utilities Information on the EDF file format can also be found in the Chapter 4 of the current document 3 7 Drift Correction In most of the template experiments a drift correction will be performed at the beginning of each trial Drift correction works by computing and applying a corrective offset to the raw eye position data It is important that before EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 49 performing a drift correction the subject be instructed to sit still and fixate on the drift correction target carefully If you need to drift correct very often
20. from the Display PC to the EyeLink II tracker is implemented by an Ethernet link Refer to the EyeLink II Programming Manual Programming EyeLink Experiments in Windows Version 2 0 for details on how to use the EyeLink II API to setup and record EDF files 4 3 The EyeLink On Line Parser The EyeLink II system incorporates a unique on line parsing system which analyzes eye position data into meaningful events and states saccades fixations and blinks For many experiments such as reading or cognitive research only the events need to be stored in the EDF file reducing its size by 80 to 95 4 3 1 Parser Operation The parser uses velocity and acceleration based saccade detection methods Because of the EyeLink II tracker s exceptionally low noise levels and high spatial resolution very little data filtering is needed and thus delay is kept small Typically the spatial noise is less than 0 005 RMS allowing a velocity EyeLink I User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 57 noise level of less than 2 second RMS to be achieved The 250 or 500Hz Hz sampling rate gives high temporal resolution of 4 or 2 milliseconds For each data sample the parser computes instantaneous velocity and acceleration and compares these to the velocity and acceleration thresholds If either is above threshold a saccade signal is generated The parser will check that the saccade signal is on or off for a critical time before deci
21. good choice fixation update interval 100 fixation update accumulate 100 4 3 8 Other Parameters The EyeLink II PARSER INI configuration file contains other commands that configure the parser These are of several types e Verification delays These set the time in milliseconds that the parser requires a detector output saccadic velocity or acceleration thresholds or missing pupil for blink to be stable before the parser changes its state and sends events to the data file or link These values have been determined empirically and there is little advantage to changing them e Parser filter types Two velocity filters are available fast and slow The fast filter works better in most cases The slow filter is less noise sensitive but increases saccade duration and decreases sensitivity slightly e oaccade extension This is intended to allow the saccade period to include the lower velocity start and end of the saccadic period This is usually disabled as its effect is minor e Internal constants These MUST NOT be changed 4 3 9 Sample Configurations The complete set of commands for the most useful tracker configurations is given below The cognitive configuration is conservative is less sensitive to noise and ignores most saccades smaller than 0 6 The psychophysical configuration is useful for neurological and smooth pursuit research and reports very small saccades It also better estimates saccade durations and averag
22. headband EyeLink card and possibly the marker set to SR Research for testing and repair This is because there are no user serviceable parts on the EyeLink II card or on the headband Be sure to follow the packing instructions you received with the system when repackaging the EyeLink II into it s shipping case Under normal circumstances SR Research will send a replacement system to you EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 89 6 System Care 6 1 Maintenance The EyeLink II system should require little maintenance under normal use The plastic parts of the headband and the leather padding may be wiped with a damp cloth if cleaning is required Metal parts of the headband and the lens of the head camera may be wiped gently with a clean dry soft cloth The lenses of the eye cameras are recessed to prevent finger contact and should only rarely require dusting with a lens brush The camera support arms may occasionally require cleaning to remove dust and oils and restore smooth motion DO NOT LUBRICATE THE ARMS OR UPPER CLAMPS cleaning should be sufficient to restore smooth operation To clean these loosen the upper clamps and allow the arms to slide down until 5mm of the arm remains above the clamp Tighten the clamp and then use a soft dry clean cloth or facial tissue to gently rub the vertical part of the arms Use light pressure and up and down strokes only After cleaning restore the arms to
23. it may be worth reviewing how subjects are set up how well the headband is balanced and fit the instructions to the subject for calibration etc and may repeat a calibration after a certain number of trials If your experiment paradigm permits it is also possible to perform an online drift correction in the middle of trial recording by the experimenter There are two ways of performing an online drift correction during recording If it is very likely that the subject will look at a particular point across trials a reference position for drift correction could be defined at that position This can be done by editing the value of online dcorr refposn in the calibr ini or final ini file under c eyelink2 exe directory of the host PC or more preferably by sending this as a command in your program When the subject is looking at the reference position pressing F9 key on the host PC or sending an online dcorr trigger command over the link will perform the drift correction Alternative an online drift correction can be performed with the aid of a mouse Record No Connection stop Record ing click Before recording add the following line to the final ini file Normal click dcorr ON Duration sec 62 Tracking Binocular 5HB Hz Pupil Data to No outputs enabled Title DCORR L 4 18 R 3 35 EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 50 Figure 3 8 Performing an online dri
24. lt ypl gt psl xpr ypr lt psr gt xvl lt yvl gt xvr lt yvr gt xr lt yr gt DATA NOTATIONS lt time gt timestamp in milliseconds xp yp monocular X and Y position data lt xpl gt lt ypl gt left eye X and Y position data lt xpr gt lt ypr gt right eye X and Y position data lt ps gt monocular pupil size area or diameter lt psl gt left pupil size area or diameter EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 80 lt psr gt right pupil size area or diameter XV lt yv gt instantaneous velocity degrees sec lt xvl gt lt yvl gt left eye instantaneous velocity degrees sec lt xvr gt lt yvr gt right eye instantaneous velocity degrees sec Xr Xyr X and Y resolution position units degree EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 81 4 9 3 Event Line Formats Each type of event has its own line format These use some of the data items listed below Each line begins with a keyword always in uppercase and items are separated by one or more tabs or spaces DATA NOTATIONS eye time lt stime gt lt etime gt lt dur gt axp ayp lt sxp gt lt syp gt lt exp gt lt eyp gt lt aps gt av pv lt ampl gt XXVI lt yvr gt lt xr gt lt yr gt 4 9 3 1 Messages which eye caused event L or R timestamp in milliseconds timestamp o
25. should settle to 1 in 220 microseconds 8 3 Digital Inputs and Outputs The digital ports are configured by the EyeLink software with AO A7 and BO B7 as inputs and CO C7 and DO D7 as outputs A digital only card is available when analog output is not required Digital outputs may be set by the write ioport command which may be issued though the link or by a button or initialization file command The port address for the C and D ports on the EyeLink analog output card are 4 and 5 EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 97 respectively Digital outputs may also be reserved for EyeLink tracker functions and writing to these bits has no effect For example when analog output is enabled the data output D7 is used as a strobe output to indicate when new analog data is available The digital inputs may be used as buttons and as input port bits which may be recorded in the EDF data file or sent as samples via the Ethernet link Button inputs may be connected to a digital output such as a printer port from a control computer and assigned functions such as starting and stopping recording or used as synchronizing marks in the data file When used as a real button for participant response the button is typically connected to ground a 10 K ohm resistor should be connected from the input to one of the 5V terminals on the connection board Buttons and input ports are defined in buttons ini with port ad
26. specified what type of events will be written to the EDF file It may be changed in the PARSER INI file of the EyeLink II tracker or may be sent over the link The command is followed by a list of data types and options selected from the list below Keyword Effect LEFT RIGHT limits data to one or both eyes usually include both LEFT and RIGHT FIXATION includes fixation start and end events FIXUPDATE includes fixation pursuit state update events SACCADE includes saccade start and end events BLINK includes blink start and end events MESSAGE includes messages ALWAYS use BUTTON includes button 1 8 press or release events INPUT includes changes in input port lines not yet supported These examples of the command are the default event set and a fixation only configuration file event filter LEFT RIGHT FIXATION SACCADE BLINK MESSAGE BUTTON file event filter LEFT RIGHT FIXATION BLINK MESSAGE BUTTON 4 7 EDF File Utilities A number of utility programs are included in the EyeLink II package to process and view EDF files The utility EDF2ASC translates EDF files into text ASC files for processing with user applications EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 73 4 7 1 EDFSCAN The EDFSCAN utility will scan and summarize the data contents of one or more EDF files listing the recording blocks and types of data it contains It will also check for file errors that may indicate a corrupt
27. the format of these lines and the order in which these lines occur Data lines consist of several types e Blank or comment lines which are ignored The first non blank character on a comment line is one of or 3 e File preamble or file description lines These begin with Usually these lines are ignored when processing the ASC file e Sample data lines Each line begins with a number representing the time of the sample e Event and data description lines Each line begins with a keyword identifying the type of data in the rest of the line 4 9 1 ASC File Structure EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 78 For sample only ASC files file structure is very simple These files are produced using the s or ne options of EDF2ASC and only sample data lines are present There is no data on what type of eye position data or which eye produced the data Recording blocks are separated by samples lines consisting of missing value data dots or the string specified with the miss option Gaps in the sequence of sample timestamps may also be used to determine sample block divisions For ASC files containing events and optionally samples the order of lines is carefully structured The order of items in an ASC file is similar to that of a sorted EDF file The file begins with a copy of the EDF file s preamble with each line preceded by The preamble reports the file version date c
28. the EyeLink II host PC install the card into an empty PCI slot and secure the rear bracket of the card with the bracket screw or card clamp depending on your computer model The EyeLink II tracker software will automatically find and use the analog card 8 2 2 Connections to Analog Card The analog card is supplied with a connection cable and screw terminal connection board Analog outputs and digital inputs and outputs are available from this card see the document included with the screw terminal board for which terminals correspond to the analog outputs digital inputs and outputs and ground or 5V It is up to each user to determine how to connect and use the analog output connections for their applications Connections to the analog outputs will depend on what these outputs are connected to typically this is another computer with an analog input card 8 2 3 Noise and Filtering It is very important to make sure these connections are made in way that does not introduce noise into the data so connections between the analog output terminals and the analog input terminals must be as short as possible If the analog input device does not have filters it may be helpful to add a conditioning filter to each analog connection A 470 ohm resistor between the output and input and a 0 1 microfarad capacitor from the input to ground will filter out most noise sources while not affecting the analog signals this is a 3 4 KHz low pass filter which
29. the computed fixation position and the fixation position for the target obtained during calibration This error reflects the gaze accuracy of the calibration In addition the average offset is used to perform an immediate drift correction The functionality available in the Validate screen is very similar to that of the Calibrate screen Validation should only be performed after Calibration To perform a validation have the subject look at the first fixation point and press the Accept Fixation button or the ENTER or Spacebar key to start the validation If auto trigger is not enabled repeat this action after each target fixation EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 23 2 3 5 2 Main Functions Press to go to the Camera Setup screen Keys ESC Press F1 to view the help menu for the Validate screen Keys Fl Press to reject the Validation value given and revert to the Calibration screen Keys ESC Press to have a automated calibration sequence Sequence pacing selected in the setup options menu Keys A Auto Trigger Press to accept fixation value only PEDES bii he dus gaze is stable eys 2 3 5 3 Key Shortcuts Key Fl Help screen A A Camera setup Key F1 ESC EM Auto calibration set to the pacing selected in Set Options menu Auto trigger ON EyeLink accepts current fixation if it is stable During Validation ESC Exit to Camera
30. to manually increase or decrease the selected camera s pupil threshold Keys and increase and decrease threshold select the sampling rate for recording Here 250 Hz is selected Note that in Pupil CR mode 500Hz is not available Keys F toggles sampling Frequency selection Toggles display of crosshair in eye camera images Keys X toggle crosshair display Toggles display of threshold coloring in eye camera images Keys T toggle threshold coloring display Select to present the camera display image on the Display Monitor To select the camera to display as a large image click on the desired image thumbnail The selected image thumbnail has a heavy border around it Here the Right Eye camera is selected Image thresholds and status are indicated below each thumbnail Keys lt and gt to move left or right on image row EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 13 Select the eye s to track during recording Here the Right eye is selected Press the Lock Tracked Eye mei Caer Right button to lock the current selection on Lock Tracked Eye the Display PC Keys R select Right Eye L select Left Eye B select Both Eyes Press Exit Setup to go to the screen Exit Setup that was available prior to accessing the Camera Setup window Keys ESC exit camera setup Press Offline to be returned to the Offline EyeLink II offline screen Keys ESC
31. 7 Fixation Updates Monitoring eye position or pupil size during fixations usually requires processing all samples produced by the tracker This is acceptable for file data but is expensive for real time systems using data sent via the link Fixation updates solve this problem by sending updates on eye position pupil size EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 60 velocity etc at regular intervals during a fixation The first update is sent one update interval after the start of the fixation and the last is sent at the end of the fixation Data is aggregated over a preset period which lowers data noise The interval between updates and the data accumulation period can both be set Fixation updates are most useful for real time display paradigms In some studies the subject is required to fixate a target while stimuli are presented Fixation updates can be used to check gaze position every 100 msec or so Computer interfaces operated via eye movements is a paradigm dramatically simplified by fixation updates Actions are triggered by gaze on an active area of the screen for a critical duration This is implemented simply by counting sequential fixation updates that fall within the area Two commands set the fixation update interval and data accumulation period in milliseconds Usually these are set to the same value An interval of zero disables fixation update An update interval of 50 or 100 msec is a
32. CTRL ALT Q will exit the EyeLink tracker program 2 3 1 Offline Screen Ethernet Connection Status Screen Navigation E a Ji JL Camera view with threshold status Figure 2 2 EyeLinkll Offline Screen 2 3 1 1 Purpose The off line mode is the default start up screen for EyeLink II The main secondary screens can be accessed via the navigation buttons on the left hand side of the screen 2 3 1 2 Main Functions Press to go to the camera setup Setup Cameras screen Keys ENTER Camera Setup Select Output to go to the output EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 10 Output screen from which you can starta manual recording session Keys O go to Output screen Select Set Options to go to the EyeLink II options screen where a variety of system options and settings can be configured Note that any value on this screen can be programmatically overridden by the API during experiment setup Keys S go to Set options Select Exit EyeLink to end the EyeLink Exit EueLink II program Keys Ctrl Alt Q Exit EyeLink Press Help F1 to access the online help page for Camera Setup All available key shortcuts are also listed on the Help screen Keys F1 open Help screen 2 3 1 3 Key Shortcuts sO Press to go to the Output screen F1 Press to view the Help screen in the help screen there is a brief overview of the role of thi
33. Data File component EyeLink Data File component Calibration and Validation options Figure 2 4 EyeLinkll Set Option Screen 2 3 3 1 Purpose The Set Options screen allows many EyeLink II tracker options to be configured manually This is useful when doing manual recording sessions that are not driven by a Display PC using the EyeLink II API When using the EyeLink II API to drive stimulus presentation these settings are normally set by the Display application via a set of API calls The Default Settings should be sufficient for many tracking applications EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 16 2 3 3 2 Main Functions Calibration Type ee n HH Pacing Interval 1000 Randomize Order Repeat First Point Force Manual Accept Lock Eye after Cal Pupil Size Data DIAMETER Eye Event Data Gaze Select the calibration type for recording Here a nine point calibration is selected New HV13 13 point calibration which works best with displays with large angular extent Keys C toggles Calibration Set the time delay for Calibration and Validation if auto trigger is selected Keys P toggles Pacing Randomize the calibration and validation fixation dot sequence selected Keys R Randomize Order Redisplay the first calibration or validation fixation dot Keys I Repeat First Point Select Force Manual Accept to manually accept each calibration and validati
34. EyeLink Il Head Fixed Eye Tracker EyeLink Il Monitor amp Keyboard Display Response Box User Manual Version 2 12 Optional Host Computer Analog Outputs Optional Digital Inputs Ethernet SR Research om EyeLin Display Computer Experimental Applications EyeLink API Library Copyright O 1997 2006 SR Research Ltd EyeLink is a registered trademark of SR Research Ltd Mississauga Canada Table of Contents 1 INEFOGUCTION e 1 I I iSupportis DOCUMENES sue line uo en depbtdbet int idee daU umo pad did 1 1 2 EyeLink II System Overview ccccccecccccccceecceescseucecuesseuseeeceeesceaeseenes 2 1 3 Byebink Il System Contieuration rer E E o coronene dan nina 2 OVMEE S E gebe arriere ee eau 3 o MEE NI SIBI Ua p mp 3 1 9 9 BYCLINK dL POI Gal uei i rti et diio d ala oua dua au o t dosi sus eu 5 LAG System SD CCIICATIONS Si D ea teo ete te ete 5 tA VACUO UIMIOUC S nese a O lots 5 1 4 2 Operational Functional Specifications 5 t43 PDVsIcal SPCCIICANONS Se Rise ii una lande 6 2 EyeLink Il Tracker Application Operation 8 2I Slane the Host Tracket ns ne RS e edd du La ar 8 2 2 Modes f Operation sedora ERR AER a Ni e i oL pale nd ou dun 8 2 3 EyeLink II Tracker Application Navigation 9 259 1 OMNES SA a dud aria Dub tiene mou duet pb nt d aC 10 2320 Camera SOIUD SCIE A se exivit itr 12 2 09 9 OL ODIOR
35. OR red background Errors are too high for useful eye tracking Observe the pattern of the errors for each of the targets If only one target has a high error the subject may simply have mis fixated that point and the validation may be repeated to check this press ESC to return to the Camera Setup screen and V to repeat the validation If a regular pattern is seen i e all fixations on the left side are too low there was probably a calibration or camera setup problem In this case press ESC to return to the Camera Setup screen and re calibrate If a binocular calibration was performed the system will automatically select the best eye to record with during the calibration To accept this selection press the ENTER key to override this selection and record in binocular mode or to select the less accurate eye make your selection using the mouse and then press the ENTER key to accept your selection Note to have the eyetracker always record in binocular mode and not to have it select the best eye a change in the default settings must be made Open the final ini file in the c eyelink2 exe directory of the host PC and add the following line select_eye_after_validation NO Often the computed gaze position shows a systematic shift of all the targets The average of this bias can be used to correct future gaze position calculations lowering tracking error By accepting the validation the system performs a gaze calculat
36. S 0 01 degree or 40 seconds of arc in pupil only mode and approximately 4 units RMS 0 022 degree or 88 seconds of arc in pupil corneal reflection mode 4 4 2 4 Gaze Resolution Data For gaze position unlike the HREF data the relationship between visual angle and gaze position is not constant The EyeLink II tracker computes and can record the instantaneous angular resolution at the current point of gaze This is measured as the units usually pixels per degree of visual angle computed for a change in x and y position separately This resolution data may be used to estimate distances between gaze positions and to compute velocities of eye movements To compute the angular distance of two points compute the x and y angular distances of the points separately by dividing the distance in pixels by the average of the resolutions at the two points then compute the Euclidean distance from the x and y distances For instantaneous velocity in degrees per second compute the x and y velocities then divide each by the x or y resolution square and add the x and y velocities and take the square root As noted above typical resolution is 22 pixels per degree Resolution is computed at the point of gaze on the display and can vary up to 1596 over the display The resolution data in an EDF file is recorded using a prescaler for extra precision and noted in the gaze position section EyeLink Il User Manual version 2 12 07 02 2006 2002 2006
37. S STEGT evecta cea bee D m Hp adu it E EPOD E 16 2 94 OSIDIAUOLI SCICCN actum did ep xi tati diga a ka SUMMER iua 21 2 30 ValidatioD SCICCN nn Mise daniel tee 23 2 30 DATE Correct SCO nan nine an 25 Zu OUT SCO EE Re de el ea MEN AN AR es a ne done 27 2 9 9 JNOCOlU SCHOOL a N in 29 2 d ls PACS aa D PAUL st ou 31 2 9 Mouse Simulation MO ne Re nee 32 2 6 Configuration Files and Experiment Directories cccceeceeeeeeeees 32 2 1 Analogs Data Type S a dei im tsar e ia nes 33 3 An EyeLink Il Tutorial Running an Experiment 35 o1 The cCamera etup SCC nes andere te due 36 3 2 Adjusting Eye Camera Position iioc ote eerte trae uoa ou e ero Rex eua 37 3 9 Aetio Pupil THES KO 1o oS TE A EA aloes anchors 40 EyeLink I User Manual 07 02 2000 2002 2006 SR Research Ltd 2 oF I ONE eae ein a Ed PAR D tL SL AU eee 42 DOr MEUHCIQETOTI enaere EA tue tetes eo nn bdo doi 47 3 6 Recording Gaze POSITION 522 4444 rade dues tip Helio TERES Ies 49 Sak OT COPeC HOM seeen din tatoo cit diode Eee dE 49 do ITS Toye bile TES da dei tuta E aun s a abre a ede ol 9 9 Eyelink I Setup SUM Hy iios de a sence a hee uf ad dime a eom ol H1O Experiment Praeter ee nos cire d Ps 92 3 11 Next Steps Other Sample Experiments 92 4 BIiCgal l pet 56 A r PT CONTRE E A EA E ee dore ate de ed estan nn 56 A SRecorcdune EDEP FUCI correer n E E E 57 4 2 1 Recor
38. S event This simply terminates the data block and specifies the time that recording ended The text files generated from EDF files by the EDF2ASC translator utility create a simplified form of START and END events A single START or END line is produced for both sample and event blocks which specifies which eye s were recorded from and whether samples events or both are present in the following data block Other data is given on following SAMPLES EVENTS PRESCALER etc lines EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 68 4 5 3 2 Fixations The on line EyeLink II tracker parser processes eye position data identifying saccades and fixations and compiling data on these conditions For fixations these data include e The time of the first and last sample in the fixation e The eye that generated the event e Start end and average HREF and gaze position data e Start end and average pupil size e Start end average and peak eye movement velocity e Start and end gaze data angular resolution All of this data may appear in the ENDFIX event that terminates the fixation Only the starting data can appear in the STARTFIX event that initiates the fixation In a sorted EDF file or a text ASC file produced by EDF2ASC that contains both samples and events the STARTFIX event will precede the first sample in the file that is part of the fixation and the ENDFIX event will follow the last sample in t
39. Setup F1 M F1 V ESC Help screen Manual validation Auto trigger turned off fixation if it is stable After Validation 2 J 4 O Fi 9 JHelecren V si Validate validation values o o o o ESC jDiscardvalidation values Auto validation set to the pacing selected in Set Options menu Auto trigger ON EyeLink accepts current EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 24 2 3 6 Drift Correct Screen P Drift Correct TCP IP Link Open Status Panel Sequence Options Tracking Binocular Pupil MOU THG HEAD ee ie Drift Correction 1 point Point 1 of 1 TRACKING OFF Calibration sequence point Camera view with threshold status Figure 2 7 EyeLinkll Drift Correction Screen 2 3 6 1 Purpose The drift correct screen displays a single target to the participant and then measures the difference between the computed fixation position during calibration validation and the target This error reflects headband slippage or other factors which are then corrected for by the measured error To perform a drift correction have the subject look at the first fixation point and press the Accept Fixation button or the ENTER or Spacebar key to start the validation If the drift correction error is too large the drift correction will be performed again If the total drift since the last ca
40. UPIL The eyes recorded will be one or two words LEFT RIGHT or both The data option keywords currently supported are o RES for resolution data both may be present o RATE for the sample rate 250 00 or 500 00 o TRACKING for the tracking mode P Pupil CR Corneal Reflection o FILTER for the filter level used O off 1 standard 2 extra e SAMPLES lt data type gt lt eyes gt lt data options gt This specifies what types of data is present in sample lines as a sequence of keywords The data type is one of GAZE HREF or PUPIL The eyes recorded will be one or two words LEFT RIGHT or both The data option keywords currently supported are o VEL for instantaneous velocity data o RES for resolution data both may be present o RATE for the sample rate 250 00 or 500 00 o TRACKING for the tracking mode P Pupil CR Corneal Reflection o FILTER for the filter level used O off 1 standard 2 extra EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 85 4 10 Processing ASC Files An ASC file is a simple text file and thus can be accessed by almost any programming language The usual way to process the file is to read each line into a text buffer at least 250 characters in size and to scan the line as a series of tokens non space character groups The first token in each line identifies what the line is First character in
41. actor of amp Tn 2 to 3 but introduces a 1 Link Analog Filter STD sumo ode ink sample feed Keys A toggles Filter Select Samples to record data samples to the EyeLink II Data File Select Events to record eye File Data Contents S the EyeLink II ata File Keys F toggles File Data Contents Save the eye position in direct to the EyeLink II EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 18 Data File Keys 3 Raw Eve Position Record eye rotation angle to the EyeLink II Data File HREF Position Keys 4 HREF Position Record gaze position data in the EyeLink II Data File output Keys G Gaze Position Record all button presses to the EyeLink II Data File Keys B Button Flags Record external device data into the EyeLink II Data File Keys I Input Port Data Select to view previous Keys ESC Previous Screen Select to view camera setup SCENE Keys ENTER Camera setup Press Help F1 to access the online help page for Set Option All available key Help F1 shortcuts are also listed on the Help screen Keys F1 open Help screen Press Revert to Last to restore the EyeLink II settings to the values Conf iguration loaded the last time the tracker was started Revert to Last Press Load Defaults to load the EyeLink II settings specified in the defaults ini file Keys L Revert to last configuration from last session Keys
42. and supporting documentation IMPORTANT Be sure you have read and agree to the end user license agreement provided in section 7 2 of this document before using the EyeLink II system NOTE Please be sure to check http www eyelinkinfo com news php for product and documentation updates as they become available 1 1 Supporting Documents This document contains information on using the EyeLink II system host PC application subject setup and calibration and the basics of running an experiment Information on system safety maintenance and storage is also provided The Appendix A of the current manual explains the use of analog output and digital inputs and outputs via a DT334 card if purchased Additional documents are also available A EyeLink II Installation Guide Describes a standard EyeLink II system layout and environmental considerations as well as the process followed to install the EyeLink II hardware and software on both the Host and Display computers B Windows Programmers Guide Provides suggestions on how to program experiments with EyeLink II in Windows including review of all sample experiments provided for Windows Document also details the EyeLink II Windows API C EyeLink Data Viewer User s Manual Introduces an optional Data analysis tool EyeLink Data Viewer which allows the displaying filtering and outputting of EyeLink I and EyeLink II EDF data D EyeLink II Scene Camera User Manual Provides intr
43. and connect to the EyeLink tracker ii Create a full screen window and sends a series of commands to the tracker to configure its display resolution eye movement parsing thresholds and data types iii Using a dialog box built into the eyelink exptkit library ask for a file name for an EDF data file which it commands the EyeLink II tracker to open on the Host PC hard disk iv Runa block of trials Each block begins by calling up the tracker s Setup menu screen from which the experimenter can perform camera setup calibration and validation Four trials are run each of which displays a single word v After all blocks of trials are completed the EDF file is closed and transferred via the link from the EyeLink hard disk to the Windows PC vi At the end of the experiment the window is closed and the EyeLink II library is closed Each trial begins by performing a drift correction where the subject fixates a target to allow the eye tracker to correct for any drift errors Press the space bar to perform the drift correction Recording is then started Recording can be stopped by pressing the Esc key on the Windows PC keyboard the EyeLink Abort menu Ctrl Alt A on the EyeLink keyboard or by pressing any button on the EyeLink button box B Text This experiment is an extension of the Simple experiment and uses a slightly more complex process for drawing to the Display PC monitor For more complex displa
44. aphics on the Display PC The advantage of the Display PC based control is that it allows the operator to work near the subject or for self setup We will perform most of the EyeLink II setup by using the Host PC keyboard EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 35 3 1 The Camera Setup Screen The first step in an eye tracking session is to set up the participant and eye tracker Begin by pressing ENTER on the Host PC s keyboard to display the Camera Setup screen You will see three camera image windows near the bottom of the display and a large image of the selected camera in the middle of the display Navigation button to access other Tracker screens are on the right while selection buttons for tracking mode and other functions are on the left of the screen Image Thresholds C amera Setu D Auto Threshold TCP IP Link Open Pupil SCreens Off line Tracking Mode M Output Record Pupil S08 Hz em WD Image Display Crosshairs Calibrate Threshold Coloring Validate DISABLED Drift Correct Image gt Remote LEFT EVE HEAD CAMERA RIGHT EYE Pupil 138 Pupil 95 NO PUPIL NO PUPIL Eye s to Track Both EREET Figure 3 1 Example Camera Setup Screen before Camera Setup Throughout the EyeLink II software you can use the Host PC mouse to select options and navigate throughout the tracker screen Almost very button has an equivalent key shortcut The key sh
45. as specified by the recording parse type command This command may be edited in the PARSER INI file of the EyeLink II tracker or may be sent over the link recording parse type data type one of PUPIL HREF or GAZE gt The data type used for parsing will always be included in the event data Other data reported for eye movement events are controlled with the file event data command This is followed by a list of data types and options selected from the list below Keyword Effect GAZE includes display gaze position data GAZERES includes units per degree screen resolution for start end of event HREF includes head referenced eye position AREA includes pupil area or diameter VELOCITY includes velocity of parsed position type average peak start and end EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 72 STATUS includes warning and error flags aggregated across event not yet supported FIXAVG include ONLY averages in fixation end events to reduce file size NOSTART start events have no data other than timestamp The file event data command may be edited in the PARSER INI file of the EyeLink II tracker or may be sent over the link Some example settings are given below GAZE GAZERES AREA HREF VELOCITY default all useful data GAZE GAZERES AREA FIXAVG NOSTART reduced data for fixations GAZE AREA FIXAVG NOSTART minimal data 4 6 3 Event Types The file event filter command
46. at produced the event The end of and summary data on the fixation is reported with the EFIX line This reports the time of the first and last sample in the fixation and computes the duration of the fixation in milliseconds The average X and Y eye position the type of position data is determined when the event was generated and the average pupil size area or diameter are reported Optionally the eye position angular resolution in units per visual degree are given as well All samples that are within the fixation will be listed between the SFIX and EFIX event for each eye simplifying data analysis 4 9 3 5 Saccades e SSACC lt eye gt lt stime gt EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 83 e ESACC lt eye gt lt stime gt lt etime gt lt dur gt lt sxp gt lt syp gt lt exp gt lt eyp gt lt ampl gt lt pv gt e ESACC lt eye gt lt stime gt lt etime gt lt dur gt lt sxp gt lt syp gt lt exp gt lt eyp gt lt ampl gt lt pv gt lt xr gt lt yr gt The start of saccades are reported with a SSACC line which can be eliminated with the EDF2ASC nse option The lt eye gt is L or R indicating the eye s data that produced the event The end of and summary data on the saccade are reported with the ESACC line This reports the time of the first and last sample in the saccade and computes its duration in milliseconds The X and Y eye position at the start and end of
47. aze positions during recording It is suggested that if possible you always calibrate on both eyes Even if you plan on recording monocularly calibrating and validating on both eyes allows the system to suggest the best setup single eye for monitoring during the EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 42 experiment If you can not calibrate with both eyes select the eye to be used by pressing the Left or Right button in the Eye to Track section of the Camera Setup screen or by pressing the E key There are several possible calibration types available each of which serves different purpose By default a nine point calibration type HV9 is used This is good for most of the eyetracking applications However if a large calibration region greater than 25 is involved in an experiment the HV13 calibration type should be used for best calibration accuracy Press the Set Options button from the Camera Setup screen to display the Set Options screen Check to ensure that the following options are selected for practice e Calibration type 9 point grid e Randomize target order YES e Auto trigger pacing 1000 msec Press the Previous Screen button when done to return to Camera Setup Begin calibration by pressing the Calibrate button from the Camera Setup menu A calibration target will appear on both the Host PC display and the Display PC monitor The subject
48. bration sequence is erased and new calibration data can then be collected This can be used to improve calibration accuracy for one or few selected points without having to restart the calibration procedure This is especially helpful for those subjects whose calibration data is hard to get When the last calibration target has been presented the calibration will be evaluated At the bottom of the Calibration screen each eye s calibration is graded and displayed as follows GOOD green background No obvious problems found with the data FAILED red background Could not use data calibration must be repeated The background colour of the message indicates the usability of the calibration We must still validate the accuracy of the calibration only serious problems can be detected here If problems are found examine the pattern formed by the pupil position cursors arrays of crosses for misplaced or missing fixations If the calibration was successful you may press the Accept button or the 1 key to accept the calibration results Pressing the Restart button or the ESC key will restart the calibration Pressing ESC twice exits to the Camera Setup screen EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 45 Some users especially the programmers in the phase of testing experiment programs may want to run calibration and validation with mouse simulation To do this first delete all of t
49. ccident abuse misapplication or service or modification by someone other than SR Research Ltd Any replacement disk is warranted for the remaining original warranty period or 30 days whichever is longer SR Research Ltd does not warrant that the functions of the software will meet your requirements or that operation of the software will be uninterrupted or error free You assume responsibility for selecting the software to achieve your intended results and for the use and results obtained from the software SR Research will fix reported software error in a best effort fashion and can not provide a guarantee of solution availability time THIS EXPRESS LIMITED WARRENTY IS IN LIEU OF ALL OTHER WARRENTIES EXPRESS OR IMPLIED INCLUDING ANY IMPLIED WARRENTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE IN NO EVENT WILL SR RESEARCH LTD BE LIABLE FOR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES Some jurisdictions do not allow limited on the duration of an implied warranty so this limitation may not apply to you In no event shall SR Research Ltd or its suppliers be liable for any damages whatsoever including without limitation damages for loss of business profits business interruption loss of business information or other pecuniary loss arising out of use or inability to use the software even if advised of the possibility of such damages Because some jurisdictions do not allow an exclusion or limitation of liability for
50. ch Ltd 93 7 2 Limited Hardware Warranty SR Research Ltd 5516 Main St Osgoode Ontario Canada KOA 2WO EyeLink II Product Hardware Limited Warranty SR Research Ltd Warrants this product to be free from defects in material and workmanship and agrees to remedy any such defect for a period as stated below from the date of original installation EyeLink II High Speed Eye Tracker Headband and Cable One 1 year parts and labor EyeLink II High Speed Eye Tracker PCI Card One 1 year parts and labor EyeLink II High Speed Eye Tracker Marker Cables One 1 year parts and labor LIMITATIONS AND EXCLUSIONS This warranty does not apply to any product which has been improperly installed subjected to usage for which the product was not designed misused or abused damaged during shipping or which has been altered or repaired in any way that affects the reliability or detracts from the performance Any replaced parts become the property of SR Research Ltd The computer system that the EyeLink II product components are integrated with are excluded from this warranty unless expressly agreed to be otherwise in writing by SR Research Ltd contact the original computer manufacturer for service and support for the computer system itself This warranty is extended to the original end purchaser only Proof of original date of installation is required for warranty service will be performed This warranty does not apply to the software component o
51. cognitive research shortening saccades and lengthening fixation durations The larger threshold also reduces the number of microsaccades detected decreasing the number of short less than 100 msec in duration fixations in the data Some short fixations 2 to 3 of total fixations can be expected and most researchers simply discard these Use of eye movement acceleration is important for detection of small saccades especially in smooth pursuit Acceleration data has much more noise than velocity data and thresholds of 4000 sec for small saccade detection and 8000 sec for reading and cognitive research are recommended Lower acceleration thresholds will produce false saccade reports Acceleration data and thresholds for the EyeLink II system may be larger than those reported for EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 59 analog eye trackers These systems use multi pole filters for noise reduction that adds delay and smoothes the data significantly reducing the measured acceleration The saccadic motion threshold is used to delay the onset of a saccade until the eye has moved significantly This can add 4 to 8 msec to the reported duration of fixations in cognitive research A threshold of 0 1 to 0 2 is sufficient for shortening saccades Larger values may be used with caution to eliminate short saccades for example a threshold of 0 4 will always merge fixations separated by 0 5 or less
52. cording EDF Files EDF files are created by the EyeLink II tracker recording eye position data events from the on line parser and button and input events These are recorded only when the tracker is in output recording mode Messages sent from applications on the Display PC through the Ethernet link may be recorded at any time Recording EDF files involves opening a data file recording data from one or more sessions in output mode and closing the file These operations can be performed manually using the EyeLink II tracker application on the Host PC or remotely from the Display PC through the Ethernet 4 2 1 Recording from the EyeLink Il Host PC In some eye tracking situations it is most convenient to initiate the recording of eye movement data directly For example displays may be generated by manually operated equipment or by non EyeLink applications Special provisions must be made for display of the calibration pattern By using the EyeLink II tracker s Output Screen files may be opened and closed and recording sessions may be started and stopped Refer to Chapter 2 of this manual EyeLink II Tracker Application Operation for information 4 2 2 Recording from the EyeLink API Most eye movement research involves running many subjects through a sequence of experimental trials with tens or hundreds of recording blocks per file This is best done by remote control over the link from an experimental application The connection
53. correction screen 2 3 2 3 Key Shortcuts lt and gt Select between left eye camera head camera and right eye camera Select Right eye for recording Select left eye for recording B Select both eyes for recording Z Z o F Togglesamplingfrequency selection A Auto threshold selected image Z o Z oO ooo o O X Toggle crosshair display T Toggle threshold coloring displa C Go to the Calibration screen O Z V jGototheValidatescren S D Go to the Drift correction screen Z Z o O Go to the Output screen V Open the Help dialog in the help screen there is a brief overview of the role of this page and the key functions for it Go to the Offline screen or exit camera setup Oo Wuxe EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 15 2 3 3 Set Options Screen Calibration and Validation Set Options Calibration Type E EEE TCP IP Link Open Pacing Interval RII 15HH Screens Force Manual Accept Tracking File Data Contents Mouse Simulation Events Conf iguration Pupil Size Data AREA File Sample Contents Revert to Last Events and Data Processing Eye Event Data Gaze saccade Sensitivity File Sample Filter OFF Link fmalog Filter OFF Analog Output Mapping Monocular Binocular Analog Output selection Data and system sensitivity EyeLink
54. ct responses and synchronizing events from the experimental application Both streams are time synchronized for easy analysis The file is organized into blocks of data one for each recording session Each block may have samples events or both Also the data items recorded in each sample or event may be configured at recording and are available at the block start to aid in analysis Samples are time stamped in milliseconds and contain monocular or binocular eye position data in eye rotation angle HREF or display gaze coordinated GAZE Pupil sizes as area or diameter are also recordable Samples may also contain eye movement resolution used to compute true velocity or saccadic amplitudes button presses or the status of digital inputs Eye movement events record eye position changes identified by the EyeLink II tracker s on line parser such as fixations blinks and saccades Both the onset and end of these events are marked allowing samples to be assigned to eye movement periods without complex algorithms Important data for analysis such as average position for fixations and peak velocity for saccades is also recorded in the events Other events record subject responses such as button presses and synchronization and data messages from applications These can be used to record the time of a change in the display or an experimental condition EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 56 4 2 Re
55. d also be that there is a problem with camera setup Please adjust as needed Indicates Status of Corneal CORNEAL ce wd OK OK OK Corneal is visible UNSEEN LATER ALS MISSING Corneal is missing The corneal status error message MISSING highlighted in red indicates that the corneal reflection is not visible to the eye camera See section 3 6 for details on how to set up corneal reflection properly Indicates Status of IR Markers OK IR Markers visible to camera SEEN MISSING at least one IR Marker is MARKERS OK missing from view CONFIG Extra IR Marker artifact detected EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 46 For the IR Markers status error message MISSING the IR Markers are not visible to the head camera This can be resolved by ensuring the headband is squarely placed on the participants head and that they are directly in front of the IR Emitters which are placed on the corners of the monitor screen in our standard setup The error message CONFIG means that the EyeLink is detecting too many IR Emitters This can be caused by another infra red source such as sunlight or the eye camera s being directed towards the head camera All status flags remain on for a minimum of 200 msec even if the condition that caused the warning or error to be raised lasted for less than 200 msec 3 5 Validation It is important that problems with the calibration be identifi
56. d with the A key and fine time with ff and U keys Have the subject turn their head to check eye corners e Select the second eye camera with lt or gt Repeat setup for this camera e Check the head camera image for missing markers and position e Press C to start calibration press ENTER to collect first fixation let sequence Press J to accept result ESC to repeat EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 51 e Press V to start validation press to collect first fixation let sequence Press J when finished e Repeat calibration if validation is poor e Press O to record eye movement data G on subject PC keyboard toggles gaze cursor on and off e Press CTRL ALT Q to exit EyeLink II 3 10 Experiment Practice The TRACK EXE program is the most flexible way to practice EyeLink II setup allowing almost any sequence of actions to be performed In real experiments the sequence of actions is much more defined Usually the experiment begins with subject setup and calibration from the Setup menu perhaps followed by practice trials and another calibration Then a series of experimental trials are performed often with a drift correction before each trial This flow allows little room for practice and makes it important that initial setup and calibration be performed correctly and carefully validated The EyeLink II tracker has a trial abort me
57. ding from the EyeLink Il Host PC 57 4 2 2 Recording from the EyeLink API 57 to he EveLInR On Line Parser orate en nee del of 20 POrSOTOD cuc MET UU 57 1 92 d asebbmualollsis edu dv p aa dna NE ao MI std ed 58 433 EV LINK Parser CODIIOBFallOl u s uot asta t veda haver ola ea ea aor aed 58 4 9 5 Parser pala VDO EN RE US Renan datant ie 59 4395 lt SACCAGIC TIresnollds ueste tee EUR e iae repo NE an 59 43 0 I ULISUIT OTOSDOIGS ne iioii o dad sensor EA 60 Z3 JIXaUOh JDUdlOS oer renonce nettet v piste ed 60 4 3 0 Other Paramete iced ded euenit teo E heehee 61 43 0 Sample CONMOULAUONS uuo eoa M oxy tac EE 61 Atk le DATA VCS NETT 62 LAT Cri ERIT Umm 62 dup JOOSMOD ARR ce dede RUE 63 Z3 PUPS L DOG serrer E E aude NE 66 AAA JUNO DA ESS RER uat oL ue aera nc iv 66 PO N S a de nn TETTE 66 BO MOSS Dm 67 BO BUON S oeae ENE nn ee E Pie 67 AOS Eye M vement EVCIIS oroia p ec tette Oe pP E E E 67 AO Setting Wile CONTONMES nie x beue E O ti 71 46T Sampe BIER 2 EyeLink I User Manual 07 02 2000 2002 2006 SR Research Ltd 3 407 12111 M 5 de EP a a E E A ES 72 A63 EVON TYPOS CD ET 13 ir DE DN Hale UUAU S ss dede 2 dansent bent ti t 73 244 EADS CAIN usi ntt mU E alae ee MU MM 74 Geo USME AC TES M HP 74 AG EDR ASC ne eee ie ea ee ee ie 75 Z 02 AVANSIQIOl ODNONS ne ete rade a eee 75 429 TC ASC Bile FORMAT SSD Nate RE dra 78 49 1 ASC Fil STUCCIU G 2er there desert cree 78 402 amp
58. ding that a saccade has begun or ended This check does not affect the recorded time of the saccade start or end but adds some delay to the real time events sent through the link During each saccade or fixation data is collected on velocity position and pupil size At the end of the saccade or fixation this data is used to compute starting ending and average position pupil size and velocity as well as peak velocity Velocity data is also converted into units of degrees per second using real time resolution computed from head camera data This data is then used to create events which are sent over the link and or recorded in an EDF file See the section Eye Movement Events in the chapter Data Files for more information on events 4 3 2 Parser Limitations The EyeLink II parser was designed for on line low delay identification of saccades and blinks Detection of very small saccades may require off line processing as the special filtering and computation of global velocity cannot be performed on line In smooth pursuit research the parser is less sensitive to small back up saccades opposite to the direction of pursuit than forward saccades due to the low peak velocity of back up saccades The parser only looks ahead in the data a short time 8 msec to compute velocity and acceleration This limits the data checking the parser can do Post processing or data cleanup may be needed to prepare data during analysis For
59. dresses of 2 for port A and 3 for port B Here is an example of defining a button on port A and assigning port B as the input port Create DUTON eZ OXOE b 4 DULEOn S SIDBUb A0 O35 gocbtrve input data porLs gt qr digital puts BUB a9 Input port Nnpuc data Mask OZEE 2 se oll PITS 8 3 1 Analog Data Output Assignments The EyeLink II system outputs analog voltages on 3 to 6 channels depending on the mode of operation monocular or binocular and the analog card configuration The monocular analog output configuration set by the Set Options menu screen should be used in most cases as it assigns the eye being actively tracked to the first 3 channels When binocular mode is selected left and right eye data is assigned to fixed channels The analog channel assignments may also be limited to 4 channels using the analog force 4channel configuration variable in analog ini This allows operation with binocular data when few analog inputs are available and when pupil size data is not required The results of all combinations of configurations and monocular binocular eye tracking modes are summarized in the table below with X and Y representing horizontal and vertical position data and P representing pupil size data EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 98 Eye Analog Channels DACO DACI DAC2 DAC3 DAC4 DACS tracking output available mode left right Monocular 6 x Y
60. e a directory on the EyeLink Host PC for the experiment copy any configuration files into this directory that need to be modified for this experiment and to invoke the tracker from this directory The EDF files for an experiment are written to a disk partition and directory based on the parameters set in the data ini file The default parameters specify that data is written to a disk partition called DATA and to a root directory called EDF If this partition directory is not found the data is written to the directory that the eyelink2 exe was started from As mentioned above you can specify an experiment specific data directory by copying the data ini file to your experiments launch directory and modifying the data drive name and data drive directory parameters This is a list of all EyeLink configuration files and what they control EYELINK2 INI The main configuration file includes in other INI files LASTRUN INI The thresholds menu choices etc from the last session DEFAULTS INI Default settings for all items in LASTRUN INI can be loaded from Setup menu EYENET INI Setup for Ethernet link driver data TCP IP address PHYSICAL INI Monitor head camera and display pixels resolution EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 32 settings All physical setup and simulation settings DATA INI Specifies where EDF files should be written to on Host PC Controls data written
61. e blue thresholded area in the display is interfering with setup press the Threshold Coloring button or T on the keyboard to remove the threshold color overlay In TRACK you can use keys on either the subject or operator PC s to perform all keyboard shortcut operations while the eye image is displayed EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 37 L3 MN E 3 toe EE ee er 3 Camera too High Camera too Low Will block view Poor calibration i Pupil too High in Pupil too Low in Image Image Figure 3 2 Size and Vertical Eye Camera Adjustments The camera may be moved toward and away from the eye until the corners of the eye are just outside the image as in the top row of Figure 12 If the eye image is too small the eye tracking resolution will be poor if too large the pupil will leave the image at large eye rotations and be lost Hold the eye camera with one hand and loosen the rod clamp for that camera with the other hand by 1 2 turn Slide the camera up or down through the rod clamp gently adjusting the vertical position of the image to keep the eye in view Remember to re tighten the rod clamp after the adjustment EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 38 Figure 3 3 Horizontal Adjustments of Eye Camera Finally the height of the eye camera below the eye may need to be adjusted as in the middle row of Fig
62. e the entire display is modified depending on the location of gaze These require high sampling rates and low delay which the EyeLink II tracker can deliver through the link This template demonstrates how to use the link s real time gaze position data to display a gaze contingent window This is an area centered on the point of gaze that shows a foreground image while areas outside the window show the background image You supply full screen sized bitmaps for these which are stored in the bmp folder You can use different images by replacing the one provided with the experiment with an image of your own with the same name F Control This template implements a computer interface that is controlled by the subject s gaze The participant can select one of a grid of letters by fixating on it The template contains code to support many rectangular selection regions but can be simplified if gaze in a single region is all that needs to be detected The image for the trial is a grid of letters G Dynamic EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 54 This template consists of four experiment blocks In the first block a red horizontal moving dot is presented which moves from left to right then back again repeatedly The second block presents a red which moves right to left then changes to when moving left to right repeatedly The third block presents white dots at three locations along the hor
63. e tie around the middle of the cable or place the supplied plastic bag over the cable 11 The marker cable should be removed from the Velcro patches on the monitor and the foam bag placed over the markers 12 Bundle the cable into the foam cutout on top of the headband cable to ensure it will fit then remove it and place it into the plastic bag 13 Place the bagged marker cable back into the cutout over the headband cable EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 91 If the EyeLink II card is also to be packaged remove it from the computer and place it into its anti static bag then into its slot in the foam Close the shipping case checking for excessive pressure that may indicate an obstruction Ensure the latches are closed the place the case inside its cardboard shipping box This box may then be sealed and shipped without additional padding by courier EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 92 7 Important Information 7 1 Safety 7 1 1 Electrical Isolation Safety Type BF equipment metal parts connected to chassis of computer may contact user Compliance with 601 1 medical equipment standards requires use of a medical grade power supply The EyeLink II system has been certified to comply with medical electrical equipment standards UL 2601 1 CSA C22 2 No 601 1 and IEC 60601 1 The electrical isolation required by these standa
64. e velocities EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 61 Cognitive Configuration recording parse_type GAZE saccade_velocity_threshold 30 saccade_acceleration_threshold 8000 saccade_motion_threshold 0 15 saccade_pursuit_fixup 60 fixation update interval O Psychophysical configuration recording parse type GAZE saccade velocity threshold 22 saccade acceleration threshold 4000 saccade motion threshold 0 0 saccade pursuit fixup 60 fixation update Interval 0 4 4 File Data Types The data contents of an EDF file are organized in two streams samples and events Samples are used to record instantaneous eye position data while events are used to record important occurrences either from the experimental application of from changes in the eye data Both samples and events can report eye data in several forms These are discussed in the description of sample data Eye movement data is parsed by the EyeLink II tracker on line and used to generate eye movement events which are discussed with application messages and button events 4 4 1 Samples samples are records of eye position pupil size and button or input states The EyeLink II tracker can record up to 500 samples per second from one eye monocular or both eyes binocular Each sample is stored as a binary record in the EDF file with simple compression used to minimize disk space Even with compression reco
65. earch Ltd 5 Saccades fixations blinks fixation updates On Line Eye Movement Analysis Eye position cursor during calibration Real Time Operator Feedback validation and recording Camera images and tracking status 1 4 3 Physical Specifications Digital Control come ale ROMDOS operati Host Operating system rating system Wi W O NT 2 XP MS D Display Operating system API icd s 95 98 2000 MS DOS Classification Class II grounding optional type BF conductive path from computer chassis to metal parts on the headband Powered from host computer power supply 160W or greater power supply recommended Medical grade power supply is required for 601 1 compliance O ti diti 15 C to 35 C 20 80 humidity non a MT condensing ambient pressure 101 kPa 10 C to 40 C 10 90 humidity non condensing Allow to warm to room temperature before unpacking or use after storage at temperatures below 10 C E EyeLink II Card Power Requirements SV 2A 12V 0 8A 12V 0 2A 22 watts FCC Part 15 Subpart B Class A unintentional radiators see statement below LY CISPR 11 1997 and EN55011 1998 Class A Group 1 ISM Industrial Scientific and Medical Equipment C EN 60601 1 2 1993 Part 1 General Requirements for Safety Collateral Standard Electromagnetic Compatibility Requirements and Tests Power Supply Requirements Storage conditions Electromagnetic compatibility and
66. ed and corrected before eye movement recordings are ruined By running a validation immediately after each calibration the accuracy of the system in predicting gaze position from pupil position is scored If performance is poor the calibration should be immediately repeated In a validation targets are presented on the subject display in random order similar to the calibration procedure When the subject fixates these the calibration is used to estimate the gaze position of the subject and the error difference between target position and computed gaze position is estimated Note since EyeLink II tracker version 2 0 a scaling factor is built in for automatically generated validation point positions to pull in the corner positions see the validation corner scaling command setting in the calibr ini file This is used to limit validation to the useful part of the display One physiological source of calibration inaccuracy is the natural variability in fixation position on targets estimated at about 0 4 RMS for the targets used in this EyeLink demonstration Vergence eye movements also contribute these can be seen clearly during validations with binocular gaze position displayed For calibrations with 9 targets it is highly likely that one or more targets will be fixated with an error of 1 or greater Poor eye camera setup can cause a highly distorted calibration pattern causing poor head position compensation and magnifying small er
67. ed for monocular data files The options nr no right and nl no left limit monocular data as well and can result in all eye movement data being removed Samples may contain several types of eye position data Only one of these types may be output in the ASC file The desired data type is specified by sg for gaze position data the default sh for HREF data and sp for raw pupil position data If the desired data type is not present in the file a warning message will be logged and another data type will be used The type of position data reported for eye movement events saccades and fixations is determined by the type of eye position data that was used in parsing the data in the EyeLink II tracker This is set with the recording parse_type command Resolution and instantaneous velocity data may be included for sample data lines as well as events Resolution data is included if the res option is specified and velocity data is included by the vel option Resolution data reported will match the type of eye position data in the file Gaze position resolution in units of pixels per visual degree is computed by the EyeLink II tracker and must be recorded in the EDF file as it cannot be computed No resolution data is available for raw pupil position data Resolution for HREF data is determined by the position itself and is computed by the EDF2ASC translator Velocity data in saccade and fixation events is reported di
68. er port of the EyeLink II host computer 8 1 Analog Data Quality The EyeLink II analog output system is intended for use with commercial data collection systems such as LabView or for backwards compatibility with existing eye tracking software and systems However analog data transfer may significantly degrade data quality compared to recording to file or digital transfer via the link Typically at least 1 or 2 bits of noise are added by the analog output cabling and re digitization of analog signal transfer The typical EyeLink noise level is 0 01 degree RMS analog data transfer can increase the noise level by a factor of 2 to 20 The EyeLink II system offers integrated data recording to file and digital data transfer through the Ethernet link which has latency comparable to the analog link and does not suffer from the time base resolution and noise degradation inherent in analog systems SR Research Ltd is committed to improving access to the Ethernet link data transfer methods and supplies an analog output option for backwards compatibility with existing experimental systems and as requested by users but does not encourage its use in new systems EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 96 8 2 Setting up the EyeLink Il Analog Card 8 2 1 Installing Analog Output Hardware The EyeLink II card must be installed before the analog card can be installed To install the analog output card open
69. era Setup Screen before Camera Setup 36 Figure 3 2 Size and Vertical Eye Camera Adjustments 38 Figure 3 3 Horizontal Adjustments of Eye Camera eese 39 Figure 3 4 Focusing the bye Cam ra e tn eiat v RA saw SUR FERE ep ERR it ex ba eee 40 Figure 3 5 Symptoms of Poor Pupil Threshold eeeeeeeeeeses 41 Figure 3 6 Corner Effects Seen with Head Rotation 42 Figure 3 7 Calibration Grid following a Good and Poor Calibration 45 Figure 3 8 Performing an online drift correction with mouse click 51 EyeLink I User Manual 07 02 2006 2002 2006 SR Research Ltd 6 Read instructions before use Type BF equipment applied parts Metal parts connected to chassis of computer may contact user Compliance with 601 1 medical equipment standards requires use of a medical grade power supply Entela Safety Mark Compliance of this product with UL 2601 1 CSA C22 2 NO 601 1 and IEC 60601 1 is certified by Entela an independent testing body CONTACT ADDRESS SR Research Ltd 9516 Main St Osgoode Ontario Canada KOA 2WO Fax 416 352 5376 Phone 613 826 2958 Toll Free Phone 1 866 821 0731 North America Only http www eyelinkinfo com EyeLink I User Manual 07 02 2000 2002 2006 SR Research Ltd T 1 Introduction This section introduces the EyeLink II system technical capabilities
70. esent on the right hand side of the Calibrate Validate Drift Correct Output and Record screens and gives the operator a complete and continuous status report of the camera images PUPIL E SIZE SIZE MISSING MISSING CORNEAL OK OK MISSING MISSING MARKERS OK MISSING CONFIG Figure 2 10 EyeLink Il Status Panel For the Pupil and Corneal sections of the Status Panel the left column corresponds to the left eye and the right column corresponds to the right eye If using a monocular recording set up the status column representing the eye not being used is disabled The Status Panel indicators are summarized as follows Pupil OK green Pupil present and can be tracked at selected sample rate SIZE yellow Occurs in pupil only 500 Hz and pupil CR tracking modes when the pupil size is larger than the maximum allowed pupil size MISSING red Pupil not present Corneal only operational in Pupil CR mode OK green Corneal reflection is present and can be tracked MISSING red Corneal reflection is not present Markers only operational when head tracking is enabled OK green All IR Markers are being tracked by the head camera MISSING red At least one IR Marker is missing from the head camera CONFIG red The head camera is seeing more than 4 IR sources When working in the Output and Record screens if the Pupil Size warning is on at least one sample was interpolated by the system and is indicated by Int appearin
71. f first sample in milliseconds timestamp of last sample in milliseconds duration in milliseconds average X and Y position start X and Y position data end X and Y position data average pupil size area or diameter average peak velocity degrees sec saccadic amplitude degrees right eye instantaneous velocity degrees sec X and Y resolution position units degree e MSG lt time gt message A message line contains the text of a time stamped message This will have been sent to the EyeLink II tracker by an application and contains data for analysis or timestamps important events such as display changes or subject responses The message text fills the entire line after the timestamp and any blank space following it 4 9 3 2 Buttons e BUTTON time gt button gt state Button lines report a change in state of tracker buttons 1 through 8 The button reports which button has changed state The state value will be 1 if the button has been pressed O if it has been released Tracker buttons may be created to monitor any digital input port bit and may be created by link commands or in the tracker configuration file BUTTONS INI EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 82 4 9 3 3 Block Start amp End e START lt time gt lt eyes gt lt types gt e END lt time gt lt types gt RES lt xres gt lt yres gt START lines mark the beginning of a block o
72. f recorded samples events or both The start time is followed by a list of keywords which specify the eyes recorded from and the types of data lines in the bloc The eyes recorded from are specified by LEFT for left eye monocular RIGHT for right eye monocular and both LEFT and RIGHT for binocular The types of data lines included are specified by SAMPLES for samples only EVENTS for events only and both SAMPLES and EVENTS for both END lines mark the end of a block of data The lt types gt are specified as it is possible to turn recording of samples and events on and off independently However this is not suggested and for most applications the lt types gt in the END line can be ignored The two values following the RES keyword are the average resolution for the block if samples are present it is computed from samples else it summarizes any resolution data in the events Note that resolution data may be missing this is represented by a dot instead of a number for the resolution 4 9 3 4 Fixations e SFIX lt eye gt lt stime gt e EFIX lt eye gt lt stime gt lt etime gt lt dur gt lt axp gt lt ayp gt lt aps gt e EFIX lt eye gt lt stime gt lt etime gt lt dur gt lt axp gt lt ayp gt lt aps gt lt xr gt lt yr gt The start of fixations are reported with a SFIX line which can be eliminated with the EDF2ASC nse option The lt eye gt is L or R indicating the eye s data th
73. f the product THIS EXPRESS LIMITED WARRENTY IS IN LIEU OF ALL OTHER WARRENTIES EXPRESS OR IMPLIED EXCLUDING ANY IMPLIED WARRENTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE IN NO EVENT WILL SR RESEARCH LTD BE LIABLE FOR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES In certain instances some jurisdictions do not allow the exclusion or limitation of incidental or consequential damages or the exclusion of implied warranties so the above limitations and exclusions may not be applicable WARRENTY SERVICE For product operation and information assistance please visit http www eyelinkinfo com and submit a support request or contact a SR Research Ltd Support representative For product repairs please contact your sales representative for appropriate instructions EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 94 7 3 Limited Software Warranty SR Research Ltd warrants that the software disks and CD s are free from defects in materials and workmanship under normal use for one 1 year from the date you receive them This warranty is limited to the original owner and is not transferable The entire liability of SR Research Ltd and its suppliers and your exclusive remedy shall be a replacement of any disk that does not meet this warranty which is sent with a return authorization number from SR Research Ltd This limited warranty is void if any disk is damaged has resulted from a
74. figuration file DATA INI or by sending commands to the tracker across the link via the API eyelink_timed_command Similar commands exist for samples and events sent over the link for real time applications EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 71 4 6 1 Sample Data The sample data written to the EDF file is controlled by the file_sample_data command which is followed by a list of data types to include A single keyword is included for each type Keyword Data Type LEFT limits data to one or both eyes usually include both LEFT and RIGHT RIGHT GAZE includes screen gaze position data GAZERES includes units per degree screen resolution at point of gaze HREF head referenced eye position data PUPIL raw eye camera pupil coordinates AREA pupil size data diameter or area BUTTON buttons 1 8 state and change flags STATUS warning and error flags not yet supported INPUT input port data lines not yet supported The default data is file sample data LEFT RIGHT GAZE GAZERES AREA STATUS Usually data for both eyes is enabled and the menus in the EyeLink II tracker are used to set which eye s are used Recording of gaze and pupil area is essential for mast work and resolution is important if velocity is to be computed later Recording of HREF data is optional 4 6 2 Event Data Eye movement events are generated by processing one of the types of eye movement data PUPIL HREF or GAZE
75. file The command line format of EDFSCAN is edfscan lt input edf file gt lt optional log file gt The input EDF file name can contain a path to a new directory or wildcards and to allow processing of multiple files If more than one file matches the input EDF filename you will be for each file on whether to process it process all file skip it or stop processing The optional log file extension LOG will record all the text printed to the screen making documentation of large sets of EDF files easier For each file scanned the following data is listed File Name File scanned Preamble Text at the start of file that can be read with a text editor It reports file version data created and any description from the application Blocks Recorded blocks of samples or events with number of samples and events duration number of fixations and blinks and any file errors Total Total time covered by file with percentage of time recorded as blocks Duration Fixations Total fixations with number of exceptionally short lt 100 msec and long gt 1500 msec Events Count of messages saccades blinks button presses Samples Total recorded samples count of missing data gaps Resolution Average angular resolution of gaze data pixels per visual degree Ordering UNSORTED message if file needs sorting During file scanning error or warning messages may be generated Any non error messages may be safely ignored Error messages ind
76. file that is part of the fixation and the ENDSACC event will follow the last sample in the fixation This allows the sample data in the files to be processed by saccade or fixation in a single pass The data contained in STARTSACC and ENDSACC events may be configured by modifying the DATA INI file for the EyeLink tracker Saccadic events may be eliminated entirely if only fixation data is required STARTSACC events may also be configured to contain only the start time of the fixation The peak and average velocity data for saccades is especially valuable for neuro psychophysical work These are the absolute velocities measured as the Euclidean sum of x and y components The EyeLink II parser computes velocity by use of a 5 sample moving filter which is equivalent to a differentiator followed by a 2 sample moving average or a 63 Hz single pole filter This is optimal for detection of small saccades minimizes extension of saccade durations and preserves saccadic peak velocities Other data in the ENDSACC event may be useful for some types of analysis The start and end position and start and end resolution may be used to EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 70 compute saccadic amplitude This is more easily done by multiplying average velocity by the saccadic duration dist 1000 0 end_time start_time 4 0 avg_velocity In general the saccadic amplitude will be slightly less than the d
77. first token Line type no token Blank line skip or or Comment line skip d Preamble line skip Digit 0 9 sample line Letter A Z Event or Specification line Once the line is identified it may be processed Some lines may simply be skipped and the next line read immediately For sample lines the tokens in the line can be read and converted into numerical values The token represents a missing value and may require special processing For lines where the first token begins with a letter processing depends on what the first token is The tokens after the first are read and desired data from the line are extracted from them Lines with unrecognized first tokens or with unwanted information can simply be skipped Processing of events and samples will depend on what type of analysis is to be performed For many cognitive eye movement analyses MSG line text specifying experimental conditions EFIX event data and BUTTON event times from each block are used to create data files for statistical analysis For neurological research samples between SFIX and EFIX events can be processed to determine smooth pursuit accuracy and gain In some cases an entire block of samples may need to be read and stored in data arrays for more complex processing For all of these the organization and contents of the ASC files have been designed to simplify the programmer s task EDF2ASC can compute velocity which saves a lot of effort for t
78. ft correction with mouse Click This will bring up an additional clickable drift correction button in the record screen Click on the Drift Corr button which will flash periodically if enabled Move the mouse cursor over the intended drift correction target and instruct the participant to fixate the target precisely Press the button only once when the participant fixates stably The drift correction may fail if there is no stable fixation data or if there is a large error between the current fixation and the target item By default the maximum acceptable error value set by the online dcorr maxangle command is 5 0 3 8 Exiting EyeLink II You can now exit EyeLink II Press the key combination CTRL ALT Q from any point in the Host PC tracker program to exit to the command prompt 3 9 EyeLink Il Setup Summary It is suggested that you try the procedures in this section until you feel comfortable with EyeLink II setup and can get reliable calibrations This is a Summary of the steps detailed in the practice session It assumes no setup problems are encountered e Start EyeLink II on the operator PC e Start TRACK on the Display PC e Fit the subject with the headband clip cable to subject s collar or suspend it Adjust forehead position and position the camera bracket bar e Press J ENTER to start Setup mode select an eye camera e Aim the first eye camera setting distance height and focus e Set the threshol
79. g Options k i Abort Trial OUR SIZE SIZE N SSINE Status Panel MISSING ALSSING ie TUT E Duration sec 5 Tracking Binocular 588 Hz Pupil TIS lata to Link Samples and Events TRACKING Analog Output Samples Title Manual recording session Camera view with Recording Status and threshold status Setup Details Figure 2 9 EyeLinkll Record Screen 2 3 8 1 Purpose A menu of options allows opening and closing EDF files setting data to be recorded analog output type and other output related options This mode always precedes manual entry into Output mode to allow parameter preview This is the only mode in which analog data is produced and is usually the source mode for link and file data Any graphics drawn on the idle mode screen are re displayed on the screen to be used as a reference for the real time gaze position cursor 2 3 8 2 Main Functions Stops the recording of data to the stop J EyeLink Data File Record ing Keys ESC EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 29 2 3 8 3 Key Shortcuts NENNEN IK EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 30 2 4 Status Panel The Status Panel allows users to monitor the status of the camera images throughout the setup calibration validation and recording phases of every experiment A visual indicator illustrated in Figure 2 10 is pr
80. g beside the Pupil label in the Status Panel All status flags remain on for a minimum of 200 msec even if the condition that caused the warning or error to be raised lasted for less than 200 msec EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 31 2 5 Mouse Simulation Mode You can use a mouse on the EyeLink II Host PC to simulate an eye to practice calibration and tracking alone or to test experiments during development is a test subject is not available Select Mouse Simulation in the Set Options screen or use the m command line option to enable mouse simulation 2 6 Configuration Files and Experiment Directories Most EyeLink options II are configured within the Host application however there are some lower level options that are specified by editing the configuration files INI or by sending commands from the subject PC via the Ethernet link The configuration files are loaded by EyeLink II from the current directory where EYELINK2 was typed from and if not found there from the directory containing the tracker program C EYELINK2 EXE This makes it possible to create custom configurations for experiments without editing the files in the C EYELINK2 EXE directory by placing the modified versions of the INI files in the directory where the EyeLink tracker is invoked from If your experiment will be using option settings that are non standard for your lab it makes sense to creat
81. gent display applications In addition on line data parsing occurs making eye events such as saccade fixation and blink available within 25 ms to the display computer The EyeLink II system consists of two miniature cameras which are mounted onto a head restraint No mirrors are used in the EyeLink II system making it very robust and easy to set up Two eye cameras allow binocular eye tracking or easy selection of the subject s dominant eye without the mechanical reconfiguration required by most eye trackers Each camera has built in illuminators digitally corrected for even lighting of the entire field of view Together with digital compensation for changes in ambient lighting this results in exceptionally stable pupil acquisition SR Research is committed to developing EyeLink based applications to support most eye tracking research applications and will make available software development tools for using the EyeLink II data link and file formats We will keep you informed of improvements in documentation and availability of these tools 1 3 EyeLink Il System Configuration Ou Gaze Video Overlay Optional Host Computer Display Analog Outputs Computer Optional Digital inputs Experimental Applications Ethernet EyeLink API Library Display Response Box Figure 1 1 Typical EyeLink Il System Configuration EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 2 1 3 1 EyeLink Il Host PC
82. gh Ethernet link or optional analog output card and writing of data to hard disk e Display has real time feedback of eye data during calibration or recording freeing display computer s monitor for calibration target and stimulus presentation e Data File viewing and conversion tools 1 3 2 EyeLink II Display PC The EyeLink II Display PC provides displays for experiments and calibration targets during eye tracker calibrations On line eye and gaze position can be received from the EyeLink Operator PC via the Ethernet link Sample EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 3 applications C source code and instructions for creating experimental applications are provided in the EyeLink II Windows developer kit DOS and MAC API s are also available on request The Display PC has the following key attributes Runs experiment application software for control of EyeLink II tracker and stimulus presentation using EyeLink II API allowing development of extensive experimental paradigms Display Applications can configure and control the EyeLink tracker and have access to real time data including gaze position response box button presses and keyboard Applications need only support display generation and control of the experiment sequence and should rely on the tracker for creating the data file and reading the response box This makes millisecond accurate display timing possible even under W
83. hat precede or follow a blink These may be artificial or be corrupted by the blink 4 9 4 Data Specification Lines Immediately following a START line several lines of data specifications may be present These lines contain more extensive data than the START line about EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 84 what data can be expected in the START END block These are most easily processed by creating a set of flags for each possible data option left eye events right eye samples sample velocity etc clearing these when the START line is encountered and setting the appropriate flags when keywords LEFT VEL etc are encountered in a data specification line e PRESCALER lt prescaler gt If gaze position data or gaze position resolution are used for saccades and events are used they must be divided by this value For EDF2ASC the prescaler is always 1 Programs that write integer data may use a larger prescaler usually 10 to add precision to the data e VPRESCALER lt prescaler gt If velocity data is present it must be divided by this value For EDF2ASC the prescaler is always 1 Programs that write integer data may use a larger prescaler usually 10 to add precision to the data e EVENTS lt data type gt lt eyes gt lt data options gt This specifies what types of data is present in event lines as a sequence of keywords The data type is one of GAZE HREF or P
84. he M cal files in the eyelink2 exe directory of the Host PC Start the EyeLink program set the Tracking option as Mouse simulation Go to the camera setup screen type C This will bring up the calibration screen Press the space bar only once to initiate the calibration process One or two crosses will be immediately printed on the screen depending on whether the tracking mode is set to monocular or binocular In addition the calibration target and the mouse cursor move to a second calibration point Press the left mouse button on the host PC Click the left mouse cursor for all of the following calibration targets until the calibration finishes The Status Panel will indicate any lapses in collecting data In normal operation the indicators are green Should any of the indicators display a colour other than green there is a problem with the setup that must be addressed to prevent data loss Indicates Status of Pupil PoE OK Pupil is visible urbt pa pater te SIZE Pupil is too large MISSING Pupil is missing The pupil status error message SIZE highlighted in yellow indicates that the size of the pupil is too large To reduce the pupil size the eye camera must be moved away from the pupil then refocusing the eye camera lens if needed The pupil status error message MISSING highlighted in red indicates that the pupil is missing from the camera view This could be that the participant is blinking It coul
85. he fixation This allows the sample data in the files to be processed by saccade or fixation in a single pass The data contained in STARTFIX and ENDFIX events may be configured by modifying the DATA INI file for the EyeLink II tracker For most research only simple fixation statistics are required such as average position and pupil size STARTFIX events may also be configured to contain only the start time of the fixation Other data in the ENDFIX event may be useful for some types of analysis The start and end position may be used to measure drift or pursuit during the fixation The resolution may be used to estimate angular distance between fixations Subtract the x and y position data for the fixations divide by the average corresponding resolution data and compute the Euclidean distance dx x1 x2 rx1 rx2 2 0 dy y1 y2 y1 ry2 2 0 dist sqrt dx dx dy dy The velocity data for fixations tends to be biased by the initial and terminal portions of the saccades that precede and follow it Average velocity is more reliable 4 5 3 3 Fixation Updates Data within a fixation can be broken into smaller time segments useful for real time analysis and control via eye movements FIXUPDATE events may be EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 69 produced at regular intervals within a fixation and contain data for a specified length of time within the fixation The da
86. he programmer writing smooth pursuit and saccadic analysis software If acceleration is needed as well subtract adjacent sample s velocities and multiply by the number of samples per second 250 or 500 4 11 An ASC File Processing Program See the ASC directory in the Developer s kit The files READ ASC C and READ ASC H implement an ASC file parser The ANA C program uses this to process trials from DEMO EXE and can be used as a template for creating your own analyzers Any program that uses the standard messages used by DEMO EXE will work with this EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 86 EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 87 5 Troubleshooting Here are some common and not so common problems that can be encountered with the EyeLink II system If the suggestions provided here do not solve the issue please contact a SR Research representative Problem Eye Camera Images are blank or blue e Ensure headband cable is connected to the EyeLink II PCI card in Host PC Be sure Host PC is OFF before connecting cable e Ensure the lens caps have been removed from the eye cameras e Auto Threshold the camera image to set the threshold properly Problem Head Camera Image is not displaying Markers e Ensure marker cable is connected to EyeLink II PCI card in Host PC Be sure Host PC is OFF before connecting cable e Auto Threshold the camera image to set t
87. he threshold properly Problem Receive Connection Error when starting Experiment on Display PC e Ensure the Ethernet cable is connected from the Display PC to the EyeLink II PCI card in Host PC e Restart the EyeLink II Tracker application on the Host PC Problem LED Warning on Host PC startup If a warning message concerning LED currents or safety circuits appears at startup or if the EyeLink software terminates with such a message there may be a problem with the headband headband cable or EyeLink card If such an error occurs 1 Make a copy of the EYE LOG file 2 Turn off the computer for at least 10 minutes to allow the protection devices on the EyeLink card to reset 3 Restart the EyeLink II system If the error reoccurs after restarting the software contact SR Research customer support with a description of the problem and a copy of the EYE LOG file from each session where the error occurred Problem Host PC Warning Message or Image Loss If an error occurs that produces a warning message or causes a loss of images in one or more cameras contact SR Research for troubleshooting instructions and be prepared to e mail the copies of the EYE LOG files Do not operate the computer with the EyeLink card installed unless directed to by SR Research If EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 88 SR Research determines that a hardware problem is likely you will be requested to return the
88. he total data range to be covered is set by the analog x range and analog y range variables These are followed by the data type and the minimum and maximum range fraction For example O to 1 0 would cover the full range of the data 0 1 to 0 9 would cover the central 80 of the data and 0 2 to 1 2 would add a 20 margin above and below the expected data range e For raw data the default range is 0 1 to 0 9 because the pupil position will never reach the edges of the eye camera image It is possible that the scaled EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 99 and transformed pupil CR data might exceed this range but in general this range will be similar to that of the camera image Raw data should be assumed to be in arbitrary units For HREF data the entire data range is assumed to be 30000 to 30000 This is about 127 This should never be exceeded The default range setting is therefore 0 0 to 1 0 The HREF data may be recovered from the voltage by the following formula HREF voltage minvoltage maxvoltage 2 60000 maxvoltage minvoltage e For gaze position data the data range is scaled to the display coordinates which are 640 by 480 at startup and may be changed via link commands The data range setting is 0 2 to 1 2 allowing 20 extra range for fixations that map to outside the display This extra data range allows for slippage or for identification of fixations outside the displa
89. icate serious file structure problems and will terminate processing of the file You may also control what is reported to you Normally only serious errors and missing samples are reported By adding the v option to the command line you may also view warnings and data on each recording block in the file 4 8 Using ASC Files The EDF file format is an efficient storage format for eye movement data but is relatively complex to support To make the data in EDF files accessible the translator EDF2ASC converts the files into a text version that is easily accessible from almost any programming language The ASC file format consists of lines of text with each line containing data fora single sample event or data parameter It is easily read and is ordered to make most data processing tasks straightforward Many translation options are available specifying the file contents EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 74 4 8 1 EDF2ASC The EDF2ASC utility reads one or more EDF files creating text files with the same name but with the ASC extension It scans the input file reordering data as required and converting samples and events into lines of text It can also compute resolutions and instantaneous velocity for sample data The ASC file are about twice as large as the original EDF files To translate an EDF file type edf2asc followed by the name of the file to be translated and any convers
90. ie LINC FMa erma o Ro a Dict Sa pa cA 79 roue MEE I Niere P ee res need der Den 82 4 9 4 Data Specification Lines 84 FLO PROCESSING ASC Piles ne ie en Le de 86 4 IL JAnooc File Processing PEFOBESTIIG dns seine 86 5 TrouDlesnoolllig ussctooco a cast ea de seu ee nasale cus tu her alertes Congo ES EYES 88 Problem Eye Camera Images are blank or blue 88 Problem LED Warning on Host PC startup cece ccc cce eee ee scenes eeneeeeennes 88 Problem Host PC Warning Message or Image Loss cecceeceeeeeeeeeeeenees 88 6 System CAO ES RSS S 90 Gel MamtenanGE 2 di ee e 90 6 2 Storage and Transportation zoo ori dence M EN 91 7 Important Information nennen nennen nnn nnn nnn nnn nnns 93 TERES Cn RISE OS SD E NURSE RERUM 93 Fidel dXiecical solatio n SAONE hob reta s healed eon aed 93 1 2 Eye Illumination Salely iei itta inda ated epus tas dan ma leon iUud 93 2 Jamtted Hardware Warranty ss sis SN ieee Men 94 4 0 Limited Software War TAN mini lettera tera Ro on E aaa enee 95 1 4 Copyrights Trademarks csssssseessesssesseseee eene ehe ehe hene 95 8 Appendix A Using the EyeLink II Analog and Digital Output Card 96 Sal Analog Data OAV 3i uote eh t Moe mat dauid hues Mod aui dh 96 8 2 Setting up the EyeLink II Analog Card 97 8 2 1 Installing Analog Output Hardware 97 0 22 CONMECHONS to Analog CAES Re en cad 97 0 2 9 INOISS ON PHONE See ed orne usitatum sers E ora 97 EyeLink
91. indows 4 infrared markers for head tracking mounted on corners of display Data File viewing and conversion tools EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 4 1 3 3 EyeLink Il PCI Card The EyeLink II PCI card performs the powerful image processing required to achieve the high temporal and spatial resolution capable with the system The PCI card is hosted in the Host PC and has connectors for e EyeLink II headband on a 5 meter cable e Head tracking markers on a 7 meter cable e Ethernet cable for Display PC connection 1 4 System Specifications 1 4 1 Tracking Modes Sample Rate Average Delay Stability Filter Off On Pupil Only 250 or 500Hz 3ms 5ms 7 ms lt 0 01 Affected by headband slip and vibration 1 4 2 Operational Functional Specifications Image Processing Fully Digital Pupil Tracking Hyper acuity Resolution Gaze lt 0 005 Velocity Noise average 0 1 of diameter Pupil Size Resolution 30 horizontal 20 vertical in pupil only mode 20 horizontal 18 vertical Eye Tracking Range Gaze Tracking Range Calibration Validation using Pupil Built in calibration validation Tolerates significant indirect IR Operating Environment EDF Data File Eye position HREF position gaze position EDF File and Link Data Types pupil size buttons messages digital inputs EyeLink I User Manual version 2 12 07 02 2006 2002 2006 SR Res
92. ing of file messages and data blocks This is useful as a summary of file structure when designing analysis software for experiments Finally message events can also be removed with the nmsg no messages option Examples of the most useful sets of sample and event selection options are edf2asc ns no samples just events edf2asc neye just samples messages button events and data block events nothing but sample data edf2asc ns neye file structure outline messages buttons data block events Add to these options any sample data selectors and eye l r data selectors required 4 8 2 4 Special Data Options The formatting of numerical data as text requires the use of a special symbol or value to indicate missing or undefined data For example eye position data is missing during a blink as no pupil is present In some EDF files required velocity or resolution data is missing By default such missing data is replaced with a dot Any string or value can be used to replace the missing data This value is specified with the miss option which is followed by the value to be used One possibility is to use a very small value such as le 8 Resolution data is not available in some EDF files or for raw pupil position data A default resolution value can be set using the defres option which is EyeLink I User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 77 followed by the x and y resolutio
93. ion correction similar to a drift correction using this data EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 48 3 6 Recording Gaze Position After the system is set up and calibrated we can monitor gaze position in real time and record it for later analysis or viewing Pressing the Output button or the O key from the Camera Setup screen will display the Output menu where eye data files EDF can be opened and closed and analog output if installed can be controlled TRACK EXE automatically opens a data file DATA EDF but you can change this by opening a new file in this menu Pressing 1 ENTER or O again will enter Output mode and start display of gaze position and data recording In this session we assume the TRACK application is running on the Display PC When TRACK senses that the Host PC has entered Output mode it sets up a recording session under its own control On the Display PC it displays a page of text or a target grid on its own screen for the subject to read alternating between recording sessions The Host PC screen will show the pattern of boxes that corresponds to each letter or word on the subject s display This serves as a reference for the gaze position cursor displayed by EyeLink II during recording allowing the operator to see where the subject is looking and detect problems with eye tracking errors or of subject inattention Applications can create similar
94. ion options Wildcards and may be used in the input file name allowing conversion of multiple EDF files to ASC files with the same name Optionally a second file name can be specified for the output ASC file Many options exist for the file conversion One set of options will be best for your work and creation of a single line batch file called for example E2A BAT will make the use of the translator easier 4 8 2 Translator Options The options for EDF2ASC are of 4 types file selection sample data event type and general data These are discussed below and then summarized in a table at the end of the section 4 8 2 1 File Selection File names for EDF file inputs are specified with the first filename on the command line This may have wildcards and to specify a set of files If more than one file matches the specification EDF2ASC will prompt for each file name Press Y to process the file N to skip it A to process all remaining files and Q to skip all files If a second file name is present in the command line it will be used to name the output file Otherwise the output file will have the same name as the input file with the extension ASC added This is the default mode if multiple files are to be translated By using the p option a destination directory or alternative file extension can be specified The translation of each file may be logged by creating a list file with the d option This is useful f
95. istance between average position of the preceding and following fixations as saccades do not include sub threshold velocity parts of the eye movement that precede and follow the rapid phase 4 5 3 5 Blinks The STARTBLINK and ENDBLINK events bracket parts of the eye position data where the pupil size is very small or the pupil in the eye camera image is missing or severely distorted by eyelid occlusion Only the time of the start and end of the blink are recorded Blinks are always preceded and followed by partial occlusion of the pupil causing artificial changes in pupil position These are sensed by the EyeLink II parser and marked as saccades The sequence of events produced is always e STARTSACC e STARTBLINK e ENDBLINK e ENDSACC Note that the position and velocity data recorded in the ENDSACC event is not valid All data between the STARTSACC and ENDSACC events should be discarded The duration of the blink may be computed by either the duration of the missing pupil between the STARTBLINK and ENDBLINK events or the difference between the ENDSACC and STARTSACC events in the sequence Fixation immediately preceding and following blinks should be examined carefully as they may have been truncated or produced by the blink process Discarding fixations shorter than 100 ms proceeding or following blinks will eliminate most artifacts 4 6 Setting File Contents The data recorded in samples and events may be set in the EyeLink II con
96. iun nent puis leu ee he Binocular 6 etx ny np Right Binocular 6 J rightX right Y right P Binocular Binocular 6 letX leftY leftP rightX right Y right P left right Monocular 4 1 X Y P J l l Binocular Monocular 4 leftX leftY rightX righty Left Binocular 4 deft X lefty l Right Binocular 4 f rightX rightY Binocular Binocular 4 letX leftY rightX righty Table 1 Analog channel data assignments 8 3 2 Analog Data Types and Ranges Both gaze and HREF position data are available for analog output These are selectable through the EyeLink II tracker s Set Options menu screen Each of these is scaled to a voltage on the analog output as described below Raw pupil or pupil CR data is also available for applications that implement their own calibrations 8 3 3 Scaling of Analog Position Data Each of the types of position data is scaled to match the selected analog output voltage range Several variables in analog ini set what proportion of the expected data range for each type will be represented at the output and what the total voltage range will be e Total analog voltage range is set by analog dac range followed by the highest and lowest voltage required The voltage range may be from 10 to 10 volts with other typical ranges being 5 to 5 or O to 10 volts e The fraction of t
97. izontal axis The final fourth block presents a white dot a few seconds later another white dot is shown The original white dot then fades away This presentation pattern is repeated EyeLink II User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 55 4 Data Files The EDF file format is used by the EyeLink II tracker and supporting applications to record eye movements and other data It is designed to be space efficient and flexible allowing for complete records of experimental sessions and data It adapts to monocular and binocular recording with backwards compatibility for future enhancements The EyeLink II EDF file format is backwards compatible with the original EyeLink EDF file format The EDF file format is a platform portable binary record of eye position and synchronization events This format is used directly for EyeLink II applications and may be translated by the EDF2ASC utility into a text format ASC file This file lists most of the important data in the EDF file in a more easily accessible format but at the expense of much larger file size Note By changing the file data filter from High to Medium or Off this will affect EyeLink Data Viewer EDF2ASC and other analysis tool data calculations 4 1 File Contents The EDF files contain two streams of data eye position samples up to 500 per second produced from the EyeLink II tracker and events eye movement events such as saccades and fixations subje
98. libration is too large the drift correct will fail and you will be prompted to perform another calibration EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 25 2 3 6 2 Main Functions Press to go to the Camera Setup Camera Setup screen Keys ESC Press F1 to view the help menu which shows all the key functions for the Help 1 Validation screen and gives an brief overview of the role of drift correction Keys ENTER Stop the Drift Correction Abort Press to accept fixation value only Accept when the participants gaze is stable Fixation Keys ENTER 2 3 6 3 Key Shortcuts ENTER Begins or accepts ESC Rejects drift correction value if one has been created or exits drift sequence F1 F1 Help screen EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 26 2 3 7 Output Screen Output TCF IT Link Open Start Recording FUPLL OK R EIZE EISE HISSIHG HISSIHG Status Panel CORNEAL OK OK FEI MG MISSING PARKERS Yh HISSI HE re tds EDF File Eyelink Data File options Tracking Binocular 58H Hz Pupil HEAT m tile Data none selected TRACK ING em File None ino File open Camera view Tracking setup and with threshold output details etatiie Figure 2 8 EyeLinkll Output Screen 2 3 7 1 Purpose The output screen is used to manually track and record eye movement data EDF files may be opened and mes
99. lues with 260 or more units per visual degree The 0 O point in the coordinate system is arbitrary as the relationship between display positions and HREF coordinates changes as the subject s head moves Even when a chinrest is used to stabilize the subject s head head rotations of several degrees can occur HREF coordinates are best used for determining angles relative to a known eye position or to measure eye movement velocities as described below The eye rotation angles may be directly computed from the HREF x y pairs There are several methods of specifying eye rotation angles The angular distance eye rotation magnitude between any two HREF points is directly computable The C code to compute this angle is given below Remember to multiply the result by 57 296 to get the angle in degrees angle acos f f x1 x2 y1 y2 sqrt f f x1 x1 yl yl ff x2 x2 y2 y2 The HREF angular resolution may be computed as the first derivative of the rate of change of HREF position with angle It is sufficient to compute the resolution separately for the x and y coordinate directions This may be used to compute true eye movement velocities by dividing computed velocity in HREF units by the resolution for the sample These formulas give the x and y resolution in units of change in HREF position per degree of visual angle xres 0 01745 FT x x y y sqrt f f y y yres 0 01745 f f x x y y sqrt f f x x
100. n values A fixed resolution value for gaze data and pupil position data may be forced by using the setres option in a similar manner Forcing use of a preset resolution may allow recovery of data where system setup was incorrect or to regularize velocity computations Suggested values of forced resolution are 200 to 400 for raw pupil position data and 22 0 for gaze position data The latter assumes standard system setup subject s eyes distant from the display by twice its width and 640 by 480 pixel display resolution 4 8 2 5 Summary of Options or nr outputs left eye data only if binocular data file r or nl outputs right eye data only if binocular data file sp outputs sample raw pupil position if present sh outputs sample HREF angle data if present Sg outputs sample GAZE data if present default res outputs resolution data if present vel outputs velocity data in samples if possible S Or ne outputs sample data only e or ns outputs event data only nse blocks output of start events nmsg blocks message event output neye outputs only non eye events for sample only files miss lt string gt replaces missing data in ASC file with lt string gt setres lt xr gt uses a fixed lt xr gt lt yr gt resolution always yr defres xr uses a default lt xr gt lt yr gt resolution if none in lt yr gt file 4 9 The ASC File Format The ASC file format is defined by the type of data lines that appear in it
101. nitialization file b File Output Eye data is available in the EyeLink II EDF file format This can be converted to an ACSII file format using the edf2asc conversion utility File output options are configurable via the Set Options screen 2 3 EyeLink Il Tracker Application Navigation The EyeLink II tracker interface consists of a set of setup and monitoring screens which may be navigated by means of the host PC mouse key shortcuts or from the Display PC application via link commands Calibrate c Set Options_ Ce Figure 2 1 Screen Overview of EyeLink Il Tracker Program Each of the modes shown in the diagram above has a special purpose Where possible each screen has a distinctive appearance as shown in the figure Screens with gray bars contain menus of key options for navigation and setup Other screens have a key navigation bar at the top of the screen and a status bar at the bottom Arrows represent the navigations possible by keys any mode is accessible by link control Note the central role of the Setup menu it serves as the mode control during subject setup EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 9 The functions of each mode and the main access keys to other modes are summarized below Pressing the on screen Help button or hitting the F1 key will open a screen sensitive Help menu listing all available key shortcuts for that screen From any screen the key combination
102. nu built in which may be used in experiments to terminate trials where setup problems are seen The Setup menu may then be used to fix eye setup or calibration and the interrupted trial may be restarted or skipped This sequence requires co operation from the experiment application and example code is given the developer s kit 3 11 Next Steps Other Sample Experiments There are several sample experiments that are valuable demonstrations of how the EyeLink II system can be used and programmed This section describes each sample experiments purpose and use For detailed information on the programming API aspect of these samples please refer to the EyeLink II Windows Programmers guide Each sample experiment can be launched from the Start Programs SR Research EyeLink gt Examples menu item All sample experiments have the following key shortcuts that can be used from the Display PC keyboard These keys are available after the experiment has started and a Data File name has been entered ENTER View camera or accept Calibration Validation if Calibration Validation has just been performed Select Camera EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 52 Perform Calibration Perform Validation PO otart experiment ESC Abort Trial A Simple The experiment is the most basic EyeLink II sample experiment The program performs the following steps i Initialize the EyeLink II library
103. oduction to an optional tool EyeLink II Scene Camera with which the users can track gaze position on a real world scene video being captured from a head mounted scene camera E EyeLink II Gaze Overlay User Manual The optional Gaze Overlay device works with the EyeLink II system to generate a real time gaze overlay graphic on an S Video source This option is often used to provide a gaze overlay onto a dynamic moving scene such as non static website AVI file or DVD movie etc This PAL NTSC composite or S Video signal is then typically saved onto a VCR or DVD recorder for analysis EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 1 1 2 EyeLink Il System Overview Video based eye tracking systems have long been acknowledged as the simplest to set up and operate However these systems also had a reputation for low data rates poor spatial resolution high noise and frequent loss of data The EyeLink technology changed all of this with custom built high speed cameras and hyperacuity image processing EyeLink II has the highest resolution noise limited at lt 0 01 and fastest data rate 500 samples per second of any other video based eye tracker today This exceptional data quality results in very low velocity noise making the EyeLink II ideal for saccade analysis and smooth pursuit studies On line gaze position data is available with delays as low as 3 milliseconds making the system ideal for gaze contin
104. on fixation point Select Lock Eye After Cal to lock the recording eye on the Display PC keyboard if performing a monocular recording In Mouse Simulation mode the Host PC mouse simulates eye movement and can be used for experiment debugging purposes Keys M toggles Mouse Simulation modes Record the participants eye area or diameter in pixels The area is recorded in image pixels The Diameter is recorded in millimeters Keys S toggles Pupil size Area or Diameter Select Eye Event Data to record the Gaze or HREF of the participant EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 17 Keys E toggles Gaze and HREF settings Defines the sensitivity of the EyeLink II parser for saccade Sensitivity NORMAL HIGH ione dim FE ormal is intended for cognitive tasks like reading while High is intended for psychophysical tasks where small saccades must be detected Keys X toggles Saccade Sensitivit Select File Sample Filter for data in the EDF file Each increase in filter level reduces noise by a factor of 2 to 3 Keys F2 toggles File Sample Filter levels Note By changing the file File sample Filter EXTRA sample filter from high to another value this will affect EyeLink Data Viewer and other analysis tool calculations SR Research Ltd recommends leaving this value set to High Select Link Analog Filter Each increase in filter level reduces noise by a f
105. or recording multiple file batch conversions Some translation examples are Edf2asc triall translates triall edf to triall asc Edf2asc triall trialla translates triall edf to trialla asc Edf2asc trial translates triall edf trial2 edf etc to triall asc trial2 asc etc Edf2asc trial p asc translates triall edf etc to asc Mtriall asc etc in asc subdirecto EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 75 Edf2asc trial p dat translates triall edf etc to triall dat etc uses dat extension Edf2asc trial d trial translates triall edf etc to triall asc etc logs to trial ist 4 8 2 2 General Data An EDF file may contain eye movement data in many types of data especially if the default EyeLink II recording parameters are used For example both left and right eye data may be present with only one eye s data used in analysis Eye position may be recorded in both gaze and HREF angular formats Both samples and events may be recorded with only events needed for analysis and samples for graphical viewing only By default EDF2ASC translates all samples and events using gaze position data only Using the command line options listed below allows the data present in the ASC file to be controlled To select one eye s data both samples and events from a binocular data file specify left or right eye data with 1 or r respectively These are ignor
106. ortcut mappings available for the currently displayed screen can be accessed via the Help button or by pressing F1 In the Camera Setup screen you can select one of the three camera views by selecting the small camera image you are interested in with the mouse or by pressing the lt and gt keys If an experiment is open on the Display PC like TRACK exe then pressing the Image Remote button from the Camera Setup EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 36 screen will start the display of an image of the selected camera on the Display PCs monitor The lt and gt keys from the Display PC can be used to change cameras from this display HINT The currently selected camera image can also be viewed from the Display PC by pressing the ENTER key on the Display PC keyboard when the tracker is in Camera Setup mode 3 2 Adjusting Eye Camera Position This section uses illustrations from the head mounted system as used on humans to explain camera setup From the Camera Setup screen select one of the eye cameras Until the cameras have been properly aimed you will probably not see the eye initially Start by rotating the selected camera up and down until part of the eye comes into view This is adjusted by lowering and raising the eye camera handle as in the bottom row of Figure 11 If the image becomes too dark or too light wait one second while the auto contrast adjusts itself If th
107. ow Shadows Figure 3 5 Symptoms of Poor Pupil Threshold Have the subject turn their head slowly from side to side while they continue to look at the eye image on the subject monitor Check for any or the conditions in Figure 15 One common problem is for shadows at the corners of the eye which can capture the pupil These may be eliminated by increasing the threshold with the ff key Be careful not to raise the threshold too much as the pupil thresholding may be poor at other eye positions as in the first image in Figure 15 The pupil on the operator display should have a box drawn around it indicating that it has been detected If a shadow captures the pupil or it is clipped by the side of the camera window as in Figure 15 the box will disappear and the pupil will be lost On the Host PC a red warning message will appear below the small camera image for the eye indicating No Pupil The threshold can also be checked and adjusted in the Camera Setup menu The camera image display should now show a thresholded image of from all cameras with the currently selected camera outlined in purple You can use f and to change the threshold on the selected camera and or to change the selected image The Camera Setup display is updated very rapidly so noise shadows etc will be easily detected You can have the subject look at the corners of the monitor and watch the pupil image for problems Pupil position can be seen by looking fo
108. pil center position or pupil minus corneal if running in pupil CR mode as measured by the image processing system This measurement is available without performing an eye EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 33 tracking calibration but cannot use the EyeLink II head position compensation system Href This measurement is related to the tangent of the rotation angle of the eye relative to the head In the default EyeLink II setup and for the 5V to 5V output range it is 5V tan angle measured separately for vertical and horizontal rotations A calibration must be performed to properly obtain this measure Gaze This is actual gaze position on the display screen fully compensated for head position A calibration must be performed to obtain this measure The EyeLink II system offers integrated data recording and digital data transfer methods which do not suffer from the timebase resolution and noise degradation inherent in analog systems EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 34 3 An EyeLink Il Tutorial Running an Experiment The following session will demonstrate and test the EyeLink Il system A summary of the setup procedure can be found at the end of the discussion This section leads you through a straightforward subject setup and pupil corneal reflection monocular eye tracking demonstration For the easiest setup you should select a
109. puts at more than twice the EyeLink II sample rate This will prevent missed samples but will still result in steps in the data Recording the digital strobe output on an analog or digital input channel in combination with the analog data allows the first data from each sample to be selected by detecting the change in value of this output By setting the duration of the strobe pulse to O the strobe output can be set to toggle between high 4 to 5 volts and low 0 to 1 volt for every sample which produces the best signal Over sampling can also be used without the strobe when the analog data is being used to a drive gaze contingent display as the time of each sample is unimportant and over sampling will minimizes total data delay EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 101
110. r 8 bits will be set to 1 if its button has changed since the last sample The least significant bit in each byte corresponds to button 1 and the most significant to button 8 4 5 Events One of the most significant aspects of the EyeLink II tracking system and the EDF file format is its on line processing of eye movement data to identify and record events such as fixations and saccades This eliminates the need for recording of sample data for many types of research and achieves a data compression of 20 1 or greater Samples need only be recorded for data validation or if sample by sample eye position or velocity is required Events can record application data such as the time of a display change and experimental conditions or real time events such as button presses Events also define the start and end of blocks of data in the EDF file allowing applications to process data recorded with different data types Each event contains one or two timestamps in milliseconds and several data fields Data for each event is compressed and an extendable data format allows compatibility with future expanded file formats EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 66 Note that not all the event data listed here is available through the EDF2ASC translator program 4 5 1 Messages The most flexible event type is the message event A message is most often text but can contain any type of binary data as well up
111. r the moving letter L for left pupil and R for right pupil in the data display EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 41 window at the bottom right If the pupil is lost its letter will disappear from the window Pupil Clipped and Lost Corner shadow captures pupil Figure 3 6 Corner Effects Seen with Head Rotation Once you are satisfied with the eye camera and pupil setup you can select the other eye camera by pressing on the desired camera image or with the lt or gt keys NOTE It is recommended that both eyes be setup for calibration even if only one is to be monitored during the experiment The EyeLink II system automatically selects the best eye for tracking after the validation stage of setup and uses that eye for recording during the experiment 3 4 Calibration The preceding steps set up the EyeLink II camera system to track the positions of the pupils of both eyes Almost all eye movement research requires information on the subject s point of gaze on a display of visual information such as a screen of text To compute this we need to determine the correspondence between pupil position in the eye camera image and gaze position on the subject display We do this by performing a system calibration displaying several targets for the subject to fixate The pupil position for each target is recorded and the set of target and pupil positions is used to compute g
112. racker screen 2 2 Modes of Operation The EyeLink II is a multipurpose high resolution real time processing system It is designed to be used in 2 different primary operation modes Link In this mode the eye tracker is partially controlled by the Display PC via the Ethernet link The degree of Display PC control is dependent only on the display application itself It is possible to have full control of the tracker via the Display PC however this also requires the most display application programming A common scenario is to have the application on the display PC control the eye tracker to start subject setup and calibration while the operator uses the EyeLink II Host PC s keyboard to remotely control the application perform drift correction and handle problems if they occur Standalone In this mode the eye tracker is an independent system controlled by the operator by the Host PC tracker interface and keyboard The Host PC is still connected to a display generating computer for the purpose of displaying calibration targets only There are 2 possible data output modes when running the EyeLink II as a standalone system These output modes are not exclusive and include EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 8 a Analog output Using the optional analog output card data is available in analog format Analog output options are configurable via the Set Options screen and in the analog ini i
113. rding 500 samples per second binocularly will create very large data files about 4K to 10K of data per second Each sample may contain several data field including e Time of the sample timestamp in milliseconds EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 62 e One or more types of eye position data monocular or binocular e Pupil size monocular or binocular e Angular resolution of eye position data e Button or input port state bits All samples contain a timestamp recorded in milliseconds The time is measured from the time when the tracker software was started This timestamp makes detection of missing samples possible as well as simplifying processing of data Usually all samples produced by the EyeLink II tracker are recorded but the tracker may be configured to record samples at a lower rate or only when significant changes in eye position occur These special modes are not used for most data as they may prevent re analysis of the EDF file Other types of sample data are discussed in greater detail below 4 4 2 Position Data Eye position data is produced by the EyeLink II tracker for one or both eyes every 2 or 4 milliseconds depending on the tracking mode and speed set It is then processed to compute eye rotation angles and to compensate for subject head motions The processed data in one or all of these forms may be recorded in the samples Data is written as x y coordinate pairs or
114. rds is more stringent than required for regular computer power supplies therefore the EyeLink II host computer requires a medical grade power supply to meet these standards The Ethernet connection to the display computer is electrically isolated and the standard EyeLink configuration the EyeLink host PC and the display PC connected by the Ethernet cable is 601 1 compliant Even with the use of a medical grade power supply direct connection of other AC powered devices to the EyeLink II host PC may provide sources of leakage currents above those permitted by the 601 1 standards For this reason digital inputs or analog outputs from the host PC and connected to another PC or to recording devices may affect the 601 1 certification Therefore these connections should not be used unless medical grade isolation is not required or isolation has been tested for the complete configuration 7 1 2 Eye Illumination Safety The EyeLink II system is compliant with the IEC 825 LED safety standard as a Class 1 LED device and incorporates an active LED current monitoring system to ensure compliance even if hardware faults occur This circuit also shuts off power to all illuminators and markers when the EyeLink II software is not running The operation of this safety system is verified when the EyeLink II software starts and LED currents are monitored continuously while the software runs EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Resear
115. reated and any description from the application Usually the preamble is ignored during analysis The sequence of events and samples in the ASC file follows strict rules These are e START events mark the beginning of each recording block and END events mark the end of each block The START events also specifies which eye s data is present and if samples events or both are present e Data specification lines follow each START event These specify the type of data in samples and events in the block and allow flexible data processing without prescanning the file e All eye movement samples and events occur between the START event and the matching END event e All events and samples appear in temporal order That is the timestamps of samples end time timestamps of eye movement end events and start time timestamps of all other events will be the same or greater than any preceding data e Eye data samples are nested between eye movement start and end event For example the first sample in a fixation will follow the SFIX event for that fixation and the EFIX event for a fixation will follow the last sample in the fixation This allows on the fly classification of samples as the data file is read Before writing an analysis program to process an ASC file it is helpful to convert a small EDF file containing the data of interest and examine it with a word processor or print it out 4 9 2 Sample Line Format sample lines contain
116. rectly if the vel option is present For samples the velocity is computed from the position and resolution data using the same processing used in the EyeLink II tracker Velocity for gaze position data cannot be computed unless gaze resolution data is also present EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 76 4 8 2 3 Sample and Event Selection The size and readability of the translated ASC file is controlled by selecting the types of events or samples present The presence of samples increases file size by a factor of 10 or 20 compared to events alone Eliminating all samples and eye movement events makes the basic structure of the data file apparent aiding design of analysis software By default both samples and events are translated into the output ASC file Samples may be eliminated with the e events only or ns no samples options All events may be eliminated with the s samples only or ne no events options This results in a file containing only sample data lines with no events comments or file structure lines More selective event filtering is possible With the nse no start events option only summary events end of fixations saccades or blinks are reported which halves the number of eye movement events and may be acceptable for hand analysis or simple cognitive experiments All eye movement events may be removed with the neye no eye option resulting in a list
117. rors Some subjects may show substantial drifts in gaze position during fixations or may not fixate carefully adding to the errors To begin the validation procedure select the Validate button or press the V key in the Camera Setup screen The operator s display will show the gaze position as a round colored cursor or two cursors in binocular mode Note the movements of the cursors and the change in relative horizontal position EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 47 vergence following saccades Once the cursor appears stable and close to the target press the ENTER key to accept the first fixation The remaining points are collected automatically or manually as in the calibration process As each fixation is collected a cross is used to mark its computed position relative to the target The error in degrees is printed next to the cross Similar to the calibration procedure the user can use the BackSpace key in the middle of validation sequence to redo data collection for the last or last few validation points collected After the final fixation is collected the average and worst errors are displayed at the bottom of the screen and the accuracy is scored Each eye is graded separately using colored messages similar to the calibration results GOOD green background Errors are acceptable FAIR grey background Errors are moderate calibration should be improved PO
118. s page and the key functions for it EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 11 2 3 2 Camera Setup Screen Image Thresholds F Cam efa Setup Auto Threshold TCP IP Link Open Screens Exit Setup Off line Tracking Mode Pupil S08 Hz Image Display Output Record set Options Help F1 Crosshairs a Calibrate Threshold Coloring E Validate DISABLED MP Drift Correct Image gt Remote ii LEFT EVE HEAD CAMERA RIGHT EYE Pupil 138 Pupil 95 PUPIL OK PUPIL OK Eue s to Track Both SET Camera Select and Status Selected eye s to track Image Display Attributes Tracking Mode Figure 2 3 EyeLink Il Camera Setup Screen 2 3 2 1 Purpose This is the central screen for most EyeLink II setup functions From this screen the eye and head tracking cameras can be set up and their images can be thresholded Eye s to be tracked tracking mode and options can also be set Calibration Validation and Drift correction can also be performed from this screen EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 12 2 3 2 2 Main Functions Auto Threshold 258 Hz Crosshairs Threshold Coloring Inage Hemate Press Auto Threshold to threshold the selected camera image In most cases auto thresholding will set the correct image threshold for the camera Keys A Auto threshold selected image Use the arrow buttons
119. sages added or data may be output via the optional Analog output card Data file contents are controlled from the Set Options screen Recording may be manually started from the Output screen or by an application via the Ethernet link Manual recording may be terminated by switching back to the to the OUTPUT screen If the recording was initiated and a menu of options will appear allowing faster drawing and file transfer 2 3 7 2 Main Functions Previous Press to go to the Previous screen Keys ESC Previous Screen EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 27 Press to go to the Camera Setup Keys ESC Camera Setup Select Set Options to go to the EyeLink II options screen where a variety of system options and settings can be configured Note that any value on this screen can be programmatically overridden by the API during experiment setup Keys S go to Set options Press Help F1 to access the online help page for Camera Setup All available key shortcuts are also listed on the Help screen Keys F1 opens Help screen Press to begin recording EyeLink data Keys Enter or O Keys O Open File 2 3 7 3 Key Shortcuts Camera Setup Screen ENTER or O Start recording Set options screen Opens EDF File EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 28 2 3 8 Record Screen Record TCP IF Link Open Stop Record ing Recordin
120. start the calibration by pressing the ESC key Press it twice once to restart and again to exit to return to the Setup menu Even though the calibration is automatic watch the operator PC s display carefully Note the position of the cross shaped pupil position markers these should form a grid shape for the 9 point calibration i e they form three parallel horizontal or close to horizontal lines and three parallel vertical or close to vertical lines see Figure 3 7 Lapses of subject attention will be clearly visible in the movements of this cursor Also visible will be any difficulties the subject has in fixating targets and most eye camera setup problems EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 44 Good Calibration Poor Calibration Figure 3 7 Calibration Grid following a Good and Poor Calibration For some subjects especially those with neurological conditions short fixations or lapses of attention can make the automated procedure unusable A manual calibration mode can be used for these subjects where the J ENTER key must be pressed to collect each fixation Pressing the M key switches automatic calibration off It may be switched back on by pressing the A key In addition the BackSpace key may be used in the middle of calibration procedure to backtrack the calibration sequence With each press of this key the data collected for the last point in the cali
121. subject for the test that can sit still when required and does not have eyeglasses Once comfortable on these subjects you can tackle more difficult setup problems During the session description we take the opportunity to discuss many important aspects of system use These may make the setup appear long but a practiced experimenter can set up a subject in less than three minutes including fitting calibration and validation IMPORTANT Ensure the Display PC is running before starting the EyeLink II Tracker application on the Host PC If the EyeLink software is not yet running on the host PC start it by typing OD C EVELINRAVEXE 2 EYELINKZ ad IMPORTANT Remember to exit the EyeLink software by pressing the key combination CTRL ALT Q Do not switch off the computer while running the EyeLink II software as data may be lost Now start a simple sample example application on the Display PC by selecting Start gt Programs gt SR Research EyeLink Examples gt TRACK EXE When TRACK starts a copyright message will appear on the Display PC and the status message at the top right should read TCP IP Link Open on the Host PC A dialog will appear on the Display PC asking you to enter a Track EDF file name Enter TEST without the Once TRACK is running control is either from the Host PC or Display PC keyboard and the application will respond the state of the EyeLink II software by drawing appropriate gr
122. ta values which means that sampling at fixed intervals makes it likely that samples might be missed sampled twice or the transition between samples might be recorded instead Since the EyeLink II tracker and most data acquisition systems rely on interrupt driven software sampling and output it is possible that time base jitter could result in missed samples or repeated recording of a single eye position sample This would appear as a step artifact in rapidly changing eye position data such as saccades or pursuit 8 5 1 Strobe Data Input The best time base method is to use the EyeLink II analog output strobe which is assigned to digital output D7 on the analog card connection board This signal can be configured to be a short or long trigger pulse which can be used to trigger hardware data acquisition on analog input devices equipped for this or to trigger interrupt driven acquisition The characteristics of this strobe pulse may be set in the analog ini file with the strobe being active high or active low and with duration between 5 and 2000 microseconds The onset of the strobe is also delayed from the time that analog outputs change in order to allow outputs to settle to the new voltages A delay of 400 microseconds is standard allowing the use of signal conditioning low pass filters as discussed earlier 8 5 2 Over sampling and Toggle Strobe Another possibility is to over sample the analog output by recording the analog out
123. ta recorded in the FIXUPDATE event is similar to that in the ENDFIX event FIXUPDATE events are most useful in real time applications using the link Recording samples in the EDF file is more useful for most psychophysical research 4 5 3 4 Saccades The EyeLink II tracker s parser detects saccades by the velocity and acceleration of the eye movements It can reliably detect saccades as small as 0 3 degrees Because of variations in acceleration profiles the onset and offset point of saccades can vary by one or two samples from ideal segmentation done by hand Nonetheless the saccadic data compiled by the parser is sufficient for most neuro psychophysical research including smooth pursuit Most cognitive research will ignore the saccadic data using the fixation data produced by the EyeLink II parser The saccadic data produced for saccades includes The time of the first and last sample in the saccade The eye that generated the event Start end and average HREF and gaze position data Start end and average pupil size Start end average and peak eye movement velocity Start and end gaze data angular resolution All of these data may appear in the ENDSACC event that terminates the fixation Only the starting data can appear in the STARTSACC event that initiates the fixation In a sorted EDF file or a text ASC file produced by EDF2ASC that contains both samples and events the STARTSACC event will precede the first sample in the
124. their fully raised position If the headband cable feels stiff or begins to form loops it has become twisted This twist must be removed to restore the flexibility of the cable and to avoid shortening its life The easiest way to untwist the cable is to hold the headband by its top clamp and rotate it through one or more turns in the direction that will undo the twist If the twist is severe it may be necessary to disconnect the headband from the EyeLink card untwist the cable and reconnect the headband Once untwisted the cable may also be relaxed by holding the cable 20 cm from the headband with the wires inside the sheath parallel then gently shaking the cable Move down the cable 30cm at a time for at least 2 meters Next gently slide your fingers along the sheath from 2 meters down the cable towards the headband to ensure that the sheath is loose near the headband EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 90 6 2 Storage and Transportation Between uses it is recommended that the EyeLink II headband be placed on a glass or foam dummy head If the EyeLink II system is not going to be used for an extended period you may wish to disconnect the headband and marker cables from the computer and pack these in the shipping case as detailed below The EyeLink II card may be left inside the host PC although it may be removed if this computer is going to be used for another purpose to prevent theft or loss
125. time position and pupil size data Optionally velocity and resolution data may be included Several possible sample line formats are possible These are listed below EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 79 Essentially each sample line begins with a timestamp This is followed by X and Y position pairs and pupil size data for each eye and optionally by X and Y velocity pairs for each eye and resolution X and Y values For binocular data the resolution is the average of the left and right eye values Missing data values are represented by a dot or the text specified by the miss option to EDF2ASC SAMPLE LINE FORMATS e Monocular lt time gt lt xp gt lt yp gt lt ps gt e Monocular with velocity lt time gt xp yp ps xv yv e Monocular with resolution time xp yp ps xr lt yr gt e Monocular with velocity and resolution time xp yp ps xv yv xr yr e Binocular lt time gt lt xpl gt lt ypl gt lt psl gt lt xpr gt lt ypr gt lt psr gt e Binocular with velocity lt time gt lt xpl gt lt ypl gt lt psl gt lt xpr gt lt ypr gt lt psr gt lt xvl gt lt yvl gt lt xvr gt lt yvr gt e Binocular with and resolution lt time gt lt xpl gt lt ypl gt lt psl gt lt xpr gt lt ypr gt lt psr gt lt xr gt lt yr gt e Binocular with velocity and resolution time xpl
126. to EDF files link PARSER INI On line parser data types configuration saccadic detection thresholds SR RESEARCH DOES NOT SUGGEST MODIFYING THIS FILE KEYS INI Special key function definitions default user menus BUTTONS INI Hardware definition of buttons special button functions Preconfigured for Microsoft SIDEWINDER PLUG amp PLAY ANALOG INI Optional analog output hardware interface configure clock strobe control COMMANDS INI Lists some useful EyeLink commands for controlling the host application via your own program Table 1 EyeLink II Configuration Files In addition other optional ini configuration files are required if scene camera and video overlay options are installed in your system If you plan to change the default settings in the ini files please cut and paste the target commands to the final ini and make the modification in that file for the ease of future maintenance 2 7 Analog Data Types Position data and pupil size data are available in several types which are selectable through the EyeLink II Set Options options screen For pupil size either pupil area or pupil diameter may be monitored These are very high resolution measurements with a typical per unit resolution of 5 um 0 005 mm Pupil size measurements are affected by eye position due to the optics of the eye and cameras Position data output can be selected from one of three types of measurement Raw This measurement is the raw pu
127. to a maximum of 300 bytes Messages are created by application software and forwarded over the link to the EyeLink tracker which timestamps the data and writes it to the EDF file The application does not need precise timekeeping since link delays are usually very low on the order of 1 or 2 milliseconds Message events are used for two main purposes They serve to precisely record the time of important events such as display changes subject responses etc They also record experiment specific data such as trial conditions Message events consist of a millisecond timestamp and the message data A message is most often text but can contain any type of binary data as well For text data a zero byte at the end of the text is recommended for compatibility with applications written in C A message data length field provides Pascal string compatibility and allows binary data to be recorded in the message Current EyeLink applications only support text messages with zero terminated strings It is also recommended that messages be shorter than 250 characters 4 5 2 Buttons Each button event records a change in state pressed or released 1 or O of up to 8 buttons or input port bits monitored by the EyeLink II tracker Button ports bits and polarity may be set in the EyeLink II tracker configuration file BUTTONS INI Each button event contains a timestamp in milliseconds of the time the button was pressed and a word of button data This
128. two pairs for binocular data The types of position data available are explained below 4 4 2 1 PUPIL Pupil position data is raw x y coordinate pairs from the eye cameras It has not been converted to eye angles or to gaze position There may be a non linear relationship between this data and true gaze position Pupil position is reported in integer values with 200 to 400 units per visual degree When a calibration has not been performed the EyeLink system cannot convert pupil data to the more useful data types Raw pupil position is useful when auto sequencing calibrations or when the application wishes to perform its own calibration Most users will not need this data type 4 4 2 2 HREF The HREF head referenced position data directly measures eye rotation angles relative to the head It does not take into account changes in subject head position and angle or distance from the display However it may be more accurate for neuro psychophysical research as it reflects real eye movement velocities and amplitudes The x y coordinate pairs in HREF data reflect the line of sight in the geometric model below EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 63 HREF Plane eye The x y positions define a point in a plane at distance f 15000 units from the eye The HREF units are independent of system setup display distance and display resolution The HREF coordinates are reported in integer va
129. ure 11 If the camera is too high the subject s view of the bottom of the display may be blocked If the camera is too low the pupil may be hidden if the subject smiles or squints and the calibration will be poor The camera height is set by swinging the camera rod in and out The proper height may be set by the curvature of the lower eyelid in the image or by observing the position of the corneal reflections in the camera image If the lower eyelid curves up at the edges smile shape the camera should be lowered If the lower eyelid curves up in the middle frown shape the camera should be raised The position of the two eye illuminator corneal reflections the 2 white circles should be at the bottom of the pupil lower the camera if they are too high Note The corneal reflections mentioned here are not the corneal reflections used by the system for headband movement compensation and are white with a position that should be at the bottom of the pupil The corneal reflection used in the Pupil CR mode is a single circle and is yellow in colour located near the top of the pupil The pupil of the eye must now be centred in the camera image Two methods can be used depending on the operator s preference and camera clamp mechanics The camera may be loosened and slid left or right to centre the pupil Squeeze the spring clamp handle to loosen and move the camera The second method is to move the nose end of the camera rod towards and
130. ve blinked press Auto Threshold again If the subject wears eyeglasses reflections may block the pupil in the image Reflections from the eye camera illuminators can be reduced by placing the eye camera near the bottom of the eyeglass lens and aiming it up at the eye If the eyeglasses have an anti reflective coating image contrast may be poor and pupil tracking may be noisy Eyeglasses also can show bright images of the IR markers mounted on the subject monitor These reflections are automatically reduced as much as possible by the EyeLink II system however not every subject with glasses will be usable Position the camera as close to the subject s glasses as possible to reduce noise The pupil threshold should be checked by looking at the green areas in the image Figure 14 shows the symptoms to look for If the threshold is too low the blue area will be smaller than the pupil and the eye tracker data will be EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 40 excessively noisy If the threshold is too high there will be shadows at the edges and corners of the eye especially when the eye is rotated Adjust the pupil threshold by using the pupil threshold adjustment buttons or with the f and keys a mnemonic is to think of the f key as increasing the blue area and the key as decreasing the blue area NE m T ER EA de as 4 Threshold Too High Noisy Good Pupil Threshold Threshold too L
131. viewed with EyeLink Data Viewer with saccades and blinks overlaid to confirm the parsing accuracy Once correct parameters are determined they can be set by EyeLink II commands over the link as part of the experimental setup or the EyeLink II configuration file PARSER INI can be edited to change the default parameters 4 3 4 Parser Data Type Three eye position data types are available from the EyeLink II tracker for each sample raw pupil position head referenced angle and gaze position see the chapter File Data Types for more information The parser can use any one of these for detecting saccades and generating data for events The parser data type is set by the EyeLink command recording_parse_type It can be changed by editing the configuration file PARSER INI or by sending a command over the link The text of the command is one of recording parse type GAZE recording parse type HREF recording parse type PUPIL 4 3 5 Saccadic Thresholds Three thresholds are used for saccade detection motion velocity and acceleration The values of these are in degrees degrees sec and degrees sec respectively The velocity threshold is the eye movement velocity that must be exceeded for a saccade to be detected A velocity threshold of 22 degrees per second allow detection of saccades as small as 0 3 sec ideal for smooth pursuit and psychophysical research A conservative threshold of 30 sec is better for reading and
132. y Scaling to recover gaze position data is more complex as the numerical value is partially dependent on the display coordinates The following formulas do the conversion in several stages with R being the voltage range proportion and S being the proportion of screen width or height R voltage minvoltage maxvoltage minvoltage S R maxrange minrange minrange Xgaze S screenright screenleft 1 screenleft Ygaze S screenbottom screentop 1 screentop 8 4 Pupil Size Data For pupil size either pupil area or pupil diameter may be monitored These are very high resolution measurements with resolution as small as 5 microns 0 005 mm Pupil size measurements are affected by eye position due to the optics of the eye and cameras and should be considered to be measured in arbitrary units with a pupil size of zero being represented by the lowest analog voltage 8 5 Time base and Data Strobe The EyeLink II eye tracker samples eye position every 2 or 4 msec and outputs analog data at 250 or 500 Hz This combination of fast sampling rate and non EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 100 continuous output differs from most eye tracking systems with analog outputs which either output continuous analog data such as limbus tracking systems or output samples at a lower rate such as 50 60 Hz video based tracking systems This causes the EyeLink II analog output to rapidly step between da
133. y such as screens of text or pictures drawing takes too long to complete in one or two display refreshes This makes the drawing process visible and there is no clear stimulus onset for reaction time measurement The code in the text template draws to a bitmap an image in computer memory not to the display then copies it to the Display PC monitor reducing the time to make EyeLink Il User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 53 the display visible This also has the advantage of making the trial code more general almost any stimulus can be displayed given its bitmap C Picture The template Picture is almost identical to Text except that images are loaded from BMP or JPEG files and displayed instead of text D EyeData This template introduces the use of the link in transferring gaze position data This data can be used for gaze contingent or gaze control type paradigms Gaze position data can be transferred in real time or played back after recording has ended which helps to separate recording from analysis The Eyedata template uses link data to display a real time gaze cursor The data is then played back after the trial drawing the saccade paths and fixation points to the screen The bitmap for the trial is a grid of letters E GCWindow The most useful real time experiment is a gaze contingent display where the part of the display the subject is looking at is changed or wher
134. y which eye generated the event If binocular data is recorded a separate start and end event is generated for each eye The time differences between eyes are very important for neurological analysis for example Start events contain the time of the start of the eye movement condition They may also contain the state of the eye at the onset of the condition for example the position and pupil size at the start of a fixation End events contain both the start and end time of the condition The end time is actually the time of the last sample in the condition so length of a condition must be computed as the difference between the end and start times plus the time between samples 2 or 4 milliseconds End events also contain summary data on the condition as well average gaze position of a fixation for example The main classes of data events are summarized below 4 5 3 1 Record Blocks Each block of recorded data in an EDF file begins with one or both ofa STARTSAMPLES or STARTEVENTS event These contain the time of the recording start and specify what data can be expected to follow This allows flexible applications to adapt to almost any file data configuration Information included in the start events include Which eye s recorded from Sample data rate Sample data contents Event data contents Event types included Gaze position and velocity prescalers Each block of recorded data ends with one or both of an ENDSAMPLES or ENDEVENT

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