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HEARLab: bringing hearing to infants

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1. In Danny s case Dr Judy s initial gain recommen dation was increased as a result of the initial corti cal test Dr Judy s fear of over amplifying Danny was lessened because she understood that part of his loss was conductive When the middle ear fluid resolves and Danny has normal tympanograms his hearing aid gain is reduced and his cortical re sponses re evaluated Who is behind this system NAL The National Acoustic Laboratories in Syd ney Australia is a large sophisticated research facil ity Audiologists and engineers at NAL set out with the explicit aim of coming up with some method for evaluating hearing aid fittings on babies diag nosed through universal newborn screening Cor tical responses quickly emerged as the most practi cal method If you have not followed the development of cor tical tests you might believe these tests are only a few years old In fact cortical responses have been measured by researchers internationally since the 1960s Their use for measuring hearing thresholds was overtaken by ABR in the 1980s ABRs had the advantage that the response shape was more predictable and responses could be observed on sleeping babies Unfortunately the very brief stim uli used for ABRs and the requirement that the baby be asleep make them less suitable than cor tical responses for evaluating aided performance Cortical responses also more completely measure the auditory system NAL has b
2. sponse We can check to insure we have not com promised the response to the extent that we no longer see cortical responses for all three speech sounds In Danny s case the response for the high frequency speech sound t is often weak the inbuilt statisti cal test indicates that a response is not reliably pres ent This may be because the high frequency gain in the hearing aid is turned down to avoid feed back However as an experiment Dr Judy Smith covered Danny s earmold with a small amount of glycerin and she carefully inserted it snugly The glycerin formed an acoustic seal and eliminated feedback during the duration of the cortical tests Under this condition the gain in the instrument could be set to the ideal level and cortical curves could then be clearly seen for all of the three speech sounds This helps Dr Judy decide that the change to the hearing aid response will be OK as long as well fitting molds are maintained for Danny Because Danny s middle ear fluid problem kept returning once the feedback problem had been re solved Dr Judy enabled the second memory in his hearing aids so that he had one gain setting that resulted in good cortical responses when his ears were clear and another gain setting that gave corti cal responses when he had flat tympanograms Tests like this help us clearly see our goal adequate amplification in all frequency zones that produces the desired cortical responses It
3. we know if amplified speech sounds are detected by the infant wearing hearing aids After a little training you learn to see whether or not the cortex is responding when speech sounds are presented A hearing aid is fitted in the usual fashion The speech consonants m g and t are presented to the infant using sound field speakers Insert earphones cannot be used you need room for the hearing aids and ear molds to be placed over and in the ears The cortical response is then measured and viewed on the monitor along with information about testing sufficiency and whether or not a cortical response is present Speech Like Test Sounds NAL did numerous studies using many different types of sounds to evoke cortical responses It was decided to limit the speech like test sounds to three test stimuli m g and t These consonants were extracted from continuous discourse spoken by a female and filtered to match the International Long term Average Speech Spectrum ILTASS A high pass filter was also applied at 250 Hz to t and g to remove additional unwanted low fre quency noise When you measure the level of these speech sounds with a sound level meter set to an impulse time setting they are within a few decibels of the long term level of speech from which they were ex tracted For example if the cortical testing is done with these consonants set to 65 dB they will be pre sented very close to the level they would
4. child s pref erences and the best strategies for preparing them for testing Respect their opinion and fol low their suggestions Try to build some rapport with the child A little physical interaction with the child while you are interviewing the parent eg patting or stroking their arm or head can be useful in gauging how they will react to the preparation for electrode sites and may possibly help the child accept it more readily Make sure the child s physical needs eg dia per changing are attended to before starting preparation for the electrode placement Have any items that might be needed eg bottles food toys close at hand in order to minimize noise and disruption during testing Check with parents to see if bottles need warm ing or food needs preparation before you start Attempt otoscopy and tympanometry first if indicated but don t persevere if it causes the child to become too active or distressed L Ask parents to switch off mobile phones or pagers as these may cause distraction to the child if they ring during testing and may also be a potential source of electrical interference Preparation of electrode sites DU Attaching the electrodes is potentially the most challenging part of the test procedure Ap proach the preparation confidently but not too forcefully Smile and talk to the child reassur ingly DU Start the preparation in a position where the child is comfortable and not
5. have in speech whose long term level was 65 dB SPL The inter stimulus duration is 1125 msec The stim ulus duration is 30 msec A hundred epochs can be presented in about two minutes These brief consonant sounds have very little of the vowel transition They are essentially vowel free stimuli that have spectral emphasis in the low mid and high frequency regions Figure 1 shows the one third octave spectra for these three speech like sounds They have the potential to give diag nostic information about the perception of speech sounds in different frequency regions ra of speech stimuli 65dBSPL m s g it 100 1000 10000 Centre frequency Hz Figure 1 The one third octave spectra for three speech sounds ml g and It Cortical ABR The cortical response CAEP is the electrical sig nal produced by the neurons in the auditory cortex of the brain We are NOT talking about the brain stem response measured in an ABR test that hap pens in the first 10 milliseconds after a stimulus has been presented Cortical measurements are done while the child is awake Brain stem tests are often done with the child asleep The Cortical response happens much later roughly 50 500 milliseconds after the onset of the signal We will return to this topic again later in this paper The Objective for the Aided ACA Test We want to be sure the infant child g
6. nectors for electrodes There are three electrodes that will be used initially in the first software mod ule one active non inverting electrode one ref erence inverting electrode and one ground elec trode However there are five spaces for future use that can hold three active electrodes one reference electrode and one ground electrode This box sends a tiny electrical signal to the elec trodes and measures the resistance between the ac tive and ground electrodes and also between the reference and the ground electrodes The cortical signals are picked up by the difference between the signals present at the three electrodes The ac tive electrode is placed at the top of the head the reference electrode at the mastoid and the ground electrode at the forehead This system uses the new active type of elec trodes that produces much stronger signals right at the head The active and reference electrodes have the active circuit element on a miniature cir cuit board which is encased in a rubber molded housing The main result of this is that the leads between the head and the rest of the electronics are much less prone to external interference than is the case with normal passive electrodes The electrode is connected to a snap connector that takes standard blue EKG sensor pads pref erably kid size Electrodes are color coded Black is ground forehead Blue is reference mastoid Yellow is active vertex Colors are m
7. threading beads puzzles colorful teething rings and so on Items that keep hands occupied are ideal for children old enough to manage them For younger children or those who are not developmentally ready to play with items toys with texture eg spiky plastic balls plastic animals etc can be interesting for the child to touch or mouth make sure you put them in the washing container after use Action toys eg water wheels small spinning tops pecking birds wobbly animals clear plastic balls that contain moving toys can be useful as long as they are not too noisy If chil dren are allowed to hold the items they should not contain small parts that may be a choking hazard and they must be easy to clean Watch that water filled toys don t leak For older infants around 24 months and over try coloring in books with big colorful cray ons play dough if past eating it or well su pervised paper with stickers or self inking stamps Books canbe good for children of allages Heavy cardboard books of various shapes or with flaps pop up features can provide hands on activity Books made of plastic ie intended for bath time can be ideal for very young children as they are easy to clean if mouthed Almost every child enjoys watching bubbles being blown The small bottles used for par ties are inexpensive and easy to use Avoid sticky bubbles that are designed not to burst They te
8. First Edition By Robert Martin Melissa Villase or Haruey Dillon Lyndal Carter Suzanne Purdy First Edition Dec 2008 This paper introduces cortical measurements and employs case studies to suggest ways to use cortical measurements to fit hearing aids and improve hearing aid outcomes for people who are difficult to test The short DVD The NAL HEARLab by Frye Electronics Inc shows the HEARLab system being used The HEARLab NAL ACA reference guide is a step by step set of instructions on how to operate the HEARLab machine Introduction We are very excited about this topic It is great fun The clinical use of cortical measurements will revo lutionize how hearing tests and hearing aid fittings are done on infants and people who cannot or will not cooperate with the hearing tests We want this paper to be a joy to read So rather than talking about the machine we want to talk about infants and the experience their families have with hearing loss This paper begins with the story of Dr Judy Smith an audiologist and two of her tiny patients sweet Suzy and precious Danny These infants and this doctor are not real people they are inventions of the authors Numerous case studies have been pulled together into this story a story of bringing hearing to infants This paper ends with the stories of John Doe and Tiffany two complicated patients This is not a scientific paper These are fun stori
9. a marked improvement in the cortical response for the low frequency em phasis speech stimulus m Judy was delighted Danny s Follow Up Visits Precious Danny was seen several times in an at tempt to deal with three problems e middle ear fluid e feedback and poorly defined cortical response for the high frequency emphasis speech sound t A month after Danny was fitted with hearing aids the middle ear fluid disappeared then returned later Dr Judy attempted to give Danny enough gain so cortical responses could be visualized how ever increases in gain precipitated feedback Sev eral sets of earmolds were tried Finally a different set of hearing aids with improved feedback cancel lation capability were used and the feedback prob lem was temporarily solved Whenever the middle ear fluid returned Dr Judy increased the gain in the low and mid frequencies not the high frequencies as increases in high fre quency gain often produced feedback the effects of middle ear fluid are usually observed in the lower frequencies not higher While Danny s case is challenging and frustrating HEARLab gives you a powerful tool that helps you decide how aggressively to amplify various frequency zones Without cortical measurements a clinician may be tempted to make a large per manent reduction in high frequency gain to avoid feedback The HEARLab test helps to show us the effects of changes we make to the hearing aid re
10. arked on the panel and on the electrodes themselves Before the start of each test tiny electrical signals are automatically delivered to the head by the electrodes to measure the skin impedance inter face A color bar is shown for the reference and test electrode green indicates good impedance 0 5k ohms yellow is satisfactory 5 10k ohms marginal 10 15k ohms and red greater than 20 k ohms indicates poor impedance It usually helps to reduce the impedance seen by the electrodes the green range is better than the other colors Be sure the skin is cleaned well before applying the elec trodes Clinical Judgment amp Expertise 12 Older brain stem units had dozens of controls most of them critically important to each measurement In contrast the new HEARLab unit looks very sim ple to use All of the decisions that are made for fil tering stimulus timing and data viewing are built into the software Much of the complexity has been removed The software provides easy to read information about the reliability of the response and whether there has been sufficient averaging to reach a con clusion that no response is present This critical information in presented with a green traffic light that illuminates when adequate sample have been obtained Prior to this point in the test it is wrong to conclude that the child is not hearing the sound The lack of a cortical response is meaningless until adequate samples have
11. at which CAEP responses are seen on the HEARLab monitor The example of Danny who has middle ear fluid helps to reveal one of the major advantages of the HEARLab tests The aided cortical assessment in cludes all parts of the pathway of hearing A test signal is emitted from a speaker and the response is observed in the auditory cortex Many factors mark edly impact the amount and quality of sound as it passes from the outside world through the hearing aid and ear and into the brain These include but are not limited to The filter in the hook of the BTE e The space residual volume between the earmold and eardrum The presence or absence of middle ear fluid The integrity of the cochlear hair cells e The integrity of the ascending auditory nerves We tend to think of the pathway of hearing as the steps or stages in hearing from the outside world to the brain We need to remember that the auditory cortex is part of the pathway Brains mature rap idly after birth The auditory cortex of infants with normal hearing organize and mature rapidly in response to sound stimulation HEARLab tests in corporate many variables HEARLab tests take us directly to the cortical response that correlates well with the perception of speech In Danny s case poorer hearing an absent ABR and the presence of middle ear fluid caused Dr Judy to worry about under amplification In Suzy s ca
12. been made The response may just be buried in the noise i e more sample may be needed to average the noise to a lower lev el Do not get the idea however that the need for clinical judgment and professional expertise has disappeared It has not The value of the data will completely depend on the skill and experience of the clinician The clinician also has a vital role in ensuring that testing conditions are optimized and explaining the testing and results to families Cortical testing can currently be done without HEARLab however the complexity of the system requires the clinician to be an expert electrophysi ologist and the cost of the system is substantial There are many variables that can alter the results of a test a few of these include restlessness seda tion age of the patient sleepiness attending or not attending to the task sweating from crying or hy per activity electrical interference developmental delay and nervous parents All patients present different challenges The proto col must be tailor made for each patient The clini cian must always be on their toes and be prepared for anything that comes their way The machine appears to be very simple to use It has few buttons to work with It automatically indicates when a response is present It automatically indicates when residual noise is low enough to take seriously the absence of a response In spite of these technological improveme
13. can be assessed NAL has had a prototype unit in operation for a few years The current production unit HEARLab H 1000 incorporates many enhancements made over this time NAL licensed the HEARLab unit to Frye Electron ics in Oregon who manufactures the system Where is cortical testing done This paper discusses two modules the aided ACA test and the threshold prediction test 8 CTE When you measure cortical responses with hearing aids the usual input level is 65 dB SPL not very soft levels No special consideration for ambient noise needs to be made for the aided ACA tests These tests can be done in a wide vari ety of reasonably quiet listening situations Family members just need to be as quiet as possible when sounds are being presented Of course we cannot stop infants from talking during the testing but we can try to engage them in activities that keep noise to a minimum Drinking from a baby train ing cup or eating soft foods that don t involve lots of chewing can be a good way to keep a little one quiet and busy The primary consideration is the comfort of the pa tient The infant must be relaxed and reasonably still Most room noise like people talking at soft levels will be factored out by the averaging of the responses that occurs within the testing system It is helpful but not necessary to do aided ACA tests in a sound booth Neuromuscular noise p
14. ded level If so you probably need to increase the gain output and repeat the tests Itis much easier to adjust the test level on the HEAR Lab system than to adjust the volume or gain of the hearing aid Most volume controls are deactivated for these fittings If you want to drop the speech intensity level 10 dB and re evaluate or increase the intensity level 10 dB and re evaluate this can be done easily with the software Testing Restless Children Under ideal situations the patient is awake calm and quiet You use all test signals to evoke corti cal responses at several intensity levels However some children and adults with special needs are difficult to test For example they may be hyperac tive or be prone to involuntary movements mak ing it difficult to get them to sit still and allow you to properly place the electrodes and do the tests In these instances you may want to consider chang 14 ing your techniques or consider alternate testing procedures The speech like signals m g and t used by the HEARLab ACA test have a much longer du ration than the click used for ABR tests It takes about a second for the brain s response to each sound to die down and for the brain to be strongly responsive to the next sound Consequently the sounds are presented a little over one second apart This period from one sound to the next is called an epoch Roughly 100 error free epochs are needed before y
15. e who use the HEARLab system understand it is a dedicated system and must only run the HEARLab software The HEARLab software has a database used to save all the patient information and the test results It also has work screens used during the testing and reporting procedures For more information see the HEARLab NAL ACA reference guide The Stimulus Controller SC The computer sends commands to the Stimulus Controller through the USB port connection Signal generation is also done here The system does not use a sound card found in many PCs This SC unit contains signal generation circuits microphone amplifiers and stimulus amplifiers SC has a number of connectors on its back panel that are used to drive the sound field speakers the insert earphones and the bone oscillator Oth er connectors that have other uses are seen on the back panel This unit has its own power supply and must be plugged into a wall outlet It supplies power to the electrode processor box via a standard multi wire cable The Electrode Processor box This box receives direct signals from the patient and it contains a meticulously crafted system of isolators that separates the main power circuitry from the patient The separation prevents the pos sibility of accidental electrical shock The primary 11 amplifier is found in the SC unit which is electri cally isolated from the patient The electrode processor box has amplifiers and con
16. earing aid fitting needs no further review Hear ing aid fittings on infants are works in progress Continuous monitoring and repetitive re evalua tions are needed If the desired cortical responses are not observed and the residual noise is low enough that a response should be visible if one was actually there then everything about the fitting must be checked e Are the electrodes still properly attached Do they still have sufficiently low imped ance Is the child still awake Were the thresholds on which the prescrip tion was based correct Were the thresholds properly transferred to the prescription software e Is the response of the hearing aid mea sured in a coupler the one prescribed for this degree of hearing loss Is there anything unusual such as a block age or a very loose fit about the earmold Typically the hearing aids are programmed by the audiologist prior to the child infant coming to the office The child and the supporting family then come to the office and the hearing aids are fitted Soon after the child is scheduled for cortical tests On a rare very calm peaceful child the cortical tests can be done while the hearing aid is attached to a separate computer used to program the hearing aid On the more typically active child the addition of extra wires and computer make everything too complicated The gain output controls can be ad justed to the desired level
17. es about a new clinical tool The profession of Audiology has changed each time a new diagnostic tool has been integrated into clin ical practice Audiologists have assimilated ABR real ear and tympanomentry into their clinical ar mamentarium We believe Audiology is about to take another step forward as cortical measurements are rediscovered and become another standard very useful diagnostic test Our professional language is jam packed with hundreds perhaps thousands of technical terms on evoked responses It is hard to keep track of all of the terms We will take big liberties with the technical language and talk about cortical curves or cortical responses please remember this is a fun story not a technical publication When we say cortical curves we are referring to the acro nym CAEP which stands for Cortical Auditory Evoked Potentials which we discuss later Cortical responses allow us to see if the patient is detecting a sound Many patients old and young cannot respond to a hearing test by rais ing their hand or repeating a word Infants cannot talk to you as you adjust the amplification Their baby brains however produce cortical responses that give us much insight into their perception of speech sounds The use of cortical measurements will not re place ABR OAEs or any other standard test Cor tical tests give us a new way a better way to see if amplified
18. es expected for babies or children or adults for auditor system matu rity appropriate to the age of the person being tested Residual noise in the waveform is continu ously calculated and traffic light indicators show when the residual noise is sufficiently low that the absence of a cortical response can be interpreted as indicating inadequate sensa tion level Use speech sounds as a stimuli and automati cally correct for the response of the loudspeak er and the room transmission characteristics Incorporation of pure tones delivered through insert earphones enable hearing thresholds to be estimated for an awake baby or adult through measurement of cortical response to tonal stimuli still with automatic statistical detection of responses Miniature pre amplifiers on the active and reference electrode connectors greatly reduce capacitive pickup of interference within the electrode leads FRYE FRYE ELECTRONICS INC P O Box 23391 Tigard OR 97281 3391 800 547 8209 Fax 503 639 0128 www frye com e mail support frye com
19. est on a happy note rather than persisting until the child and potentially the parent is distressed This is especially im portant if the child will have to attend on an other occasion Appendix B Translation of research to HEARLab a clinically practical instrument Research finding or practical problem ad dressed Cortical response shapes vary widely from person to person Response latency varies with the maturity of the auditory system Inadequate averaging or excessive move ment by the children creates variability in the age waveform that can mask the under lying cortical response Predicting audibility of speech sounds from pure tones measurements of threshold and hearing aid performance is very complex and error prone ABR is best measured when the baby is asleep but babies are not always asleep when needed Cortical responses are best measured when the baby is awake making the techniques complementary Electrical interference from the room adds to measurement noise and can make it slow or impossible to measure a valid response Clinical implementation or solution An automated statistical detection method that does not require any apriori assumptions about the normal response shape that com bines information from different parts of the response and that shows the probability of the response being evoked by the stimulus Normative data built into the software display the range of latenci
20. estrained or restricted in their movements Where possible try to let them settle into a po sition which they prefer A recliner chair works well as it can be used for adult testing as well L Use washable covers on the chair eg bath toweling and change between assessments to maintain hygiene This makes dribbles and food spills easier to contain and reduces par ents inclination to perform immediate clean ups which can disrupt the testing Have tis sues or baby wipes at hand if needed L Have a container on hand to collect items that require cleaning according to infection con trol guidelines eg toys that have been in the child s mouth L Some younger infants may be comfortable in a rocker Fraser chair but don t rock the baby during recordings Bounces can be evident in recordings and rocking can make a child sleepy DU Fluorescent lighting can cause problems of electrical interference Incandescent lighting should be used in preference As well as pro viding a technical advantage incandescent lamps can create a pleasant relaxed ambience for children and parents Novelty lamps eg artificial fish tanks lava lamps as well as providing illumination can provide the child with visual distraction L It is important that the tester is able to moni tor the test environment and the baby s state throughout the test A strategically placed video camera can be extremely helpful i
21. ests She concludes the initial results provided better amplification She is now less concerned about the possibility of over ampli fication Note In Suzy s case comprehensive diagnostics tests OAEs ABRs were done before the corti cal measurements ACA so no unaided testing was done If OAE and ABR information had not been available then the first cortical measurement would have been an unaided study using tonal stimuli If you suspect the child has auditory neuropathy dys synchrony it is recommended you do unaid ed tests CTE before the aided tests ACA It is difficult to predict the audiogram from the ABR for these babies Danny Danny is a robust beautiful high energy infant His mother had a difficult long duration labor that ended in an emergency cesarean section Danny was large at birth over nine and a half pounds a well developed infant His Apgar and other birth scores were all normal Danny is held by his father and intently watches TV while the cortical tests are done Danny is test ed while wearing his high power hearing aids one at a time The test signal is set to 65 dB SPL Dr Judy sets the ave gain of the hearing aids to 55 dB a flat frequency response Danny has fluid in his middle ears that has prob ably been there since birth His tympanograms are flat A note about middle ear fluid was placed in his chart He will be rescheduled sooner than nor mal fo
22. ets the infor mation across the frequency spectrum of normal conversational speech Low mid and high pitched speech like sounds are presented to the infant at the normal speech level 65 dB SPL while the in fant is wearing a hearing aid The cortical respons es are studied If needed the amplification can be changed and the cortical curves re evaluated to study the fitting If no response is observed with a high level of am plification and if the averaged waveform has a sufficiently low level of residual noise more on this later supplements to hearing aids cochlear implant education using sign language etc can be considered Let s take a look at how Suzy and Danny were fit ted with hearing aids Suzy was born with moder ate severe hearing loss Danny has mixed profound hearing loss complicated because he has fluid in his middle ears Two questions haunt the professional fitting hear ing aids First Is the patient getting enough sound to develop speech and language And second Is the patient getting too much sound am I caus ing discomfort or endangering the patient s hear ing with excessive amplification We will look at these two questions as we discuss the stories of Suzy and Danny Cortical testing helps us directly answer the first question and sometimes gives us insight into the second question Suzy Suzy is a beautiful three month old infant girl She is very little She has a quiet
23. f the arrangement of the test booth makes it difficult to maintain a clear view A video camera that works well in low light is recommended DU Where the tester is in a separate observation room an audio monitor is essential in monitor ing the ambient noise level in the test environ ment to ensure consistent stimulus delivery and is also useful in communicating with the distracter Preparation for testing DU Children generally have a short attention span and their mood and state can change quickly Have all test equipment switched on checked and calibrated before the child arrives Have the recording system software open and ready on the impedance check screen to avoid unnec essary delays If testing is with hearing aids on change the batteries and check the devices on arrival Hav ing another staff member do this while you are interviewing the parent this will minimize de lay in commencing testing Ensure that the parent understands what is in volved in the test The child is more likely to be relaxed and cooperative during the assessment if their parent is confident and relaxed about what is happening Make the parent comfortable Providing a hot drink or glass of water can help put parents at ease It is a good idea to have a safe place to put a drink beside a parent so that it cannot be knocked onto baby or electrical equipment Ensure the parent feels in control of the situa tion Seek their advice about the
24. he ENT and the dis charge has stopped Quickly with the love and support of teaches counselors and foster parents she learned to come out of her protective shell She was placed in a normal classroom Not all people have wonderful lives Sweet Tiffany had had a terrible life one that tears your guts out when you think about it Tiffany was surviving the only way she knew how She acted deaf even though she had pretty good hearing Tiffany was not able to respond accurately to the Margaret s tests Margaret had been told by the teachers that Tiffany could not talk so she as sumed Tiffany had a severe hearing loss and be lieved incorrectly that Tiffany needed high power hearing aids The beauty of cortical tests is that while not all people can raise their hand when they hear a test signal the response can be seen with only passive cooperation from the patient The cortical response correlates highly with perceived speech We may prefer to use direct speech tests but these the pa tient to respond by repeating the words But often the patient cannot do this Tiffany could not do this when she was first seen by Margaret at school The story of HEARLab is more than a story about anew machine It is a story about bringing hearing to infants babies and older people It is a beautiful story about helping children like Tiffany Today Tiffany can raise her hand when Margaret presents a pure tone and asks
25. he child is five to ten years old 100 0 100 200 Time ms Figure 2 Grand average adult N 14 CAEP waveform for the eight tonal and speech stimuli recorded at Cz 300 400 500 200 Time ms 300 Figure 3 Grand average N 20 infant cortical waveforms recorded at Cz 15 The curves for adults Figure 2 usually have an initial positive peak at about 50 msec followed by an obvious trough negative peak near 100 msec This peak and trough are poorly developed or completely absent in infants By adult years over the age of twenty the dominant component is a negativity 80 120 msec that is preceded and fol lowing by positive components i e P1 at 50 to 70 msec and P2 at 150 200 msec Davis 1965 Notice that the vertical scale is 1 25 uV in the adult graphic in contrast to 5 uV for the infants The re sponse of the infant is more robust Infants often have a broad rounded peak at about 200 msec This is the curve HEARLab seeks to detect When infants with normal hearing are test ed these curves are often seen The intensity level of the infant response is much higher than that of the adult To summarize Adult CAEPs e Have a positive peak near 50 milliseconds e And an obvious trough negative peak near 100 milliseconds e And a large positive peak near 200 millisec onds The end of the curve the tail seen be tween 400 500 msec is near zer
26. he child overheat This can result in electrodes lifting and the reject rate increasing If the child gets very restless it can be better to suspend testing than let it proceed until they are hot and bothered Distraction techniques O The distracter is best seated in a comfortable position at or below the child s eye level Care must be taken to maintain an appropriate posi tion in relation to the speaker if the stimulus is presented free field Have a wide selection of age appropriate toys that are not too noisy Keep toys and other dis traction aids in easy reach to minimize noise and disruption as the test proceeds Choose toys that can be cleaned according to infection control procedures Toys that can t be cleaned eg soft toys should be kept out of the child s reach For very young infants the main aim of distrac tion is to keep them alert and awake they do not have the motor skills to pull at the leads or electrodes Mobiles hand and finger puppets are all useful items Visual novelties eg toys with lights and motion can be excellent Some mechanized toys are too noisy to use while the testing is in progress but can be good to use during breaks in order to regain a child s inter est and increase alertness Toys that are used for VROA distraction are generally suitable for children in the 7 24 month age group Examples include stacking plastic rings or cups farm animals large count ing and
27. her to indicate when she hears the tone But there was a time when Tiffany could not raise her hand so we turned to her cortical re sponses that said in effect to us I can hear I can hear A new chapter in the profession of Audiology has just opened Major advances in research by scientists around the world and particularly in the USA have shown us the importance of corti cal responses in indicating not only the detection of sounds but the maturity of the auditory system in the cortex NAL have added to this research by focusing on the automated detection of responses to speech sounds in infants All of this research has been brought together into modern computer tech nology and hardware Frye Electronics Inc have produced this as an easy to use clinically practi cal reasonably priced machine that can measure and analyze evoked cortical responses Now the fun begins We have the opportunity to do a bet ter more certain job of bringing hearing to infants and people who have problems with responding in regular auditory testing The authors predict this new technology will gen erate so much excitement that it will not be long before you see audiologists and their little patients on many of the most watched TV talk shows NOTE Lyndal intends to edit the following infor mation and add as an Appendix to the final version of the user manual Initially prepared for report of clinical evaluation by LC 9 Ap
28. hild s own earmold and hear ing aid switched off Some infants have tiny ear canals that become oc cluded easily External ear tissue in infants is very soft and pliable and can collapse easily Before cortical tests are given it is a good idea to do an otoscopic exam and check the ear canals for debris and the middle ears for fluid Obviously we do not want the ear canal to be obstructed during the test Earmolds and insert earphones hold the infant s ear canal open If you attempt to measure an un aided response on an infant with the ACA test using a sound field speaker you need to be care ful and insure the ear canal stays open when the child is held by the parent If ear canal collapse is in question switch to the CTE test and use insert earphones Also little heads need to be supported Have the parent hold the infant in their arms with the babies head held safely in their hand Make sure that the hearing aid microphone ports are not obstructed when baby nestles back on Mom or Dad s lap Cortical Responses CAEP cortical auditory evoked potentials James W Hall NI New Handbook of Auditory Evoked Responses discusses the Auditory Late Response ALR The maximum response is typically ob tained for moderate 50 60 dB verses high intensity stimuli The response is highly susceptible to altera tions in state of arousal sleep stages and to the effects of drugs such as sedatives e C
29. ho has been deprived of sound and the latencies should decrease in the months following effective aiding or implantation HEARLab also displays p values describing the likelihood that the responses to different sounds are different from each other These are based on another statistic MANOVA or multi variate analysis of variance Cortical vs Brain Stem Tests There is considerable published research on the at tempt to use ABR in fitting hearing aids Most pub lications point to the complications Few authors report success The primary test signal for ABR is the click a sound that is very short in duration Clicks tend to saturate the amplifier and they are incompatible with the processing delay of the digi tal hearing aid A click cannot engage the compres sion circuits in a hearing aid in a realistic manner The cortical response is seen around 200 millisec onds in infants and the stimulus used to elicit the response is about 30 ms long This stimulus dura tion is considerably longer than the attack time in most but not all digital hearing aids thus allow ing the compression circuits to stabilize For hear ing aids with very slow compression the child may have lower audibility for connected speech than he she does for the isolated speech sounds used within HearLab Cortical testing also has one other major advantage in contrast with ABR The electrical events we are measuring are much larger and closer to our e
30. is difficult to achieve this 13 level of amplification on a day to day basis But at least we have a clear view of our goal Until prov en different by additional tests when Danny is old enough for reliable behavioral testing adequate amplification in all zones is important The three input levels 55 65 75 dB SPL The HEARLab ACA unit has three input level set tings 55 65 and 75 dB SPL Most aided ACA testing will be done at 65 dB SPL to simulate the presentation of speech at the normal level Most hearing aid fittings will be in the right ballpark and the aided tests ACA will confirm the adequa cy of the fitting If good responses are observed at 65 dB SPL it helps to reduce the input level to 55 dB SPL and gather additional data If good responses are seen at 55 dB SPL you have no fear that the fitting has in adequate amplification you may or may not have excessive amplification On the other hand if there are no responses marked as significant at 65 dB SPL increase the input level to 75 dB and continue the tests If good responses are seen at 75 dB you may decide that the hearing aid fitting is possibly a little weak i e you need to increase the gain a bit If no responses are seen using the 75 dB SPL input despite the noise traffic light being green you know that something is significantly wrong You need to check the hearing aid and be sure the gain output is at your recommen
31. isposable electrodes a spot of double sided tape the type used for retaining hearing aids on the underside of the plastic tab of the electrode stud can give a firmer hold particu larly for mastoid or forehead sites ie where the skin is free of hair A headband is very helpful in keeping the elec trodes in place particularly at the vertex but some children are less accepting of wearing a headband than others To make wearing a headband more appealing to the child choose colorful soft and stretchy materials Give older children a choice of colors or designs eg have a selection of different mo tifs sewn on a selection of headbands Having a choice of girls or boys styles can be im portant to the child and sometimes also to the parent Use fabrics that are easy to wash and dry after use Dividing the top of the headband before use by cutting a slit a few inches long across its centre allows a section of fabric to be stretched for ward to hold the forehead electrode in place Passing the leads under the headband can help reduce pulling and strain on the electrode site during the test Elastic bandage particularly of material that al lows the ends to adhere without pins or tape eg peg bandage can be a reasonable alter native but tends to be more fiddly to put on than a headband If an inexpensive type is cho sen it can also be disposed of after use which can be an advantage Micro
32. l the screening are referred to an audiologist who specializes in pediatric evaluations 2 ABRor ASSR otoacoustic emission OAEs and immittance audiometry tympanom etry and acoustic reflex testing are often used in these evaluations After the initial pediatric hearing evaluation children who have hearing problems are scheduled for a pediatric hearing aid evaluation impres sions are made and hearing aids are or dered 3 The aids are programmed when they are received from the factory The audiologist uses current guidelines NAL or DSL i o to prescribe the gain and output The child and the family are scheduled and the hear ing aids are fitted Considerable counseling is done and the family is taught how to care for the hearing aids 4 The child is then scheduled for cortical test ing It is at this point that the HEARLab becomes invaluable The HEARLab test ing sequence is ideal for infants who have documented hearing loss and have been fit ted with hearing aids HEARLab helps to confirm that the hearing aids have been ad justed to the prescription and that these set tings are indeed meeting the child s needs Cortical tests are also ideal for any child that has developmental delay and cannot respond reliably to behavioral testing or for that matter people of any age who can not reliably respond 5 Follow up visits should be done regularly to ensure that the child is receiving proper amplification Depe
33. ldren can almost always be seen when the stimulus is 10 dB above behavioral threshold What Is a HEARLab system The patient s point of view There are two very different perspectives of HEAR Lab the family and patient point of view and the Audiologist s The HEARLab unit allows audiologists to cre ate a picture of the electrical activity of the brain when speech sounds are detected in the auditory cortex We see the evoked responses on the com puter monitor and the test results are saved in the computer s data base This is important informa tion to professionals but exciting emotionally loaded information to the parents of these children Suzy and Danny s parents are delighted with the graphs that show their babies can hear speech with their hearing aids on We should give colored copies of these evoked respons es to the patient s family Parents treasure items like the ultra sound recording of the baby three months after conception We need patient friend ly words to put on our graphs something like The first sounds Suzy heard Or Danny s brain saying Yes I can hear Most labs have photo boards that are full of thank you letters and photographs of the patient We suggest you make space for this board and ask patients for thank you letters and photos to display on the board This board will become the heart of HEARLab Parents will be drawn to this s
34. lec trodes On page three of his New Handbook of Auditory Evoked Responses James W Hall dis cusses the size voltage of the various test data ABR Cortical Auditory Late Responses etc He says Activity arising from the higher regions of the auditory system the cerebral cortex involves hundreds of thousands perhaps millions of brain cells The electrodes are also relatively close to the sources of this activity Therefore these responses tend to be somewhat larger in size amplitude on the order of 5 to 10 uV In contrast activity gen erated by the ear auditory nerve and brainstem which involves fewer neural units and may arise at a further distance from the electrodes may be extremely small on the order of 0 10 to 0 5 uV Ok changing the subject let s look at a couple of older patients John Doe John Doe is a thirty eight year old gentleman with a pending Workman s Compensation case He worked at a noisy fabrication plant for fourteen years He says the noise exposure hurt his ears and he cannot hear The Workers Comp specialist at the plant sent him to North Shore Audiology They gave John several hearing tests and fitted him with a pair of BTE hearing aids on trial John s first hearing test showed a sloping 65 85 dB hearing loss bilaterally for air conduction the bone conduction scores were near 50 dB He was re ferred to an ENT for the conductive component but pneumo otosco
35. ly studied first Speech sounds are presented at a normal speech level 65 dB SPL from a nearby speaker The CAEPs Cortical Auditory Evoked Potentials are viewed on the monitor The real ear equipment Dr Judy uses recommends 35 dB of ave gain the gain averaged for the fre quencies of 500 1000 and 2000 Hz for medium intensity input signals Note for simplicity we use term ave averaged gain Dr Judy is worried about over amplification in Su zy s case she has a marked startle response when the hearing aids are switched on Dr Judy s testing strategy is to do the tests at the recommended level 16 65 dB SPL Then if Suzy is not too restless she plans to reduce the gain and continue the study The cortical test is done with the stimulus set to 65 dB SPL normal speech level As the data start to accumulate the cortical response is quickly and clearly seen on the monitor and the statistical cal culator indicates that it is a real response i e one related to the stimulus Dr Judy is delighted that the fitting is in the right ball park These gain settings are then recorded as Suzy s recommended amplification level The right hearing aid is then fitted and the process repeated After the initial ACA tests Dr Judy markedly low ers the gain of one of the instruments and she re starts the study After about 100 epochs she stops the test the cortical response was obscure not as clear as the initial t
36. mother an old fashioned unsupportive father who is in denial of her hearing loss As Suzy grows up her family will say she is a graceful shy quiet but a sophisticated young lady The story of Suzy has a happy ending With well fitted hearing aids She hears well She gets a top notch education and a job she loves She becomes very successful But before this wonderful story can happen Dr Judy has to fine tune this tiny infant s amplification and deal with a father who does not believe Suzy should be wearing hearing aids Suzy is held in her mom s lap electrodes are placed on the top of her head her forehead and mastoid She is restless but calms down after she nurses Heavy nursing is avoided as infants tend to go to sleep if they nurse a lot Suzy wants to go to sleep but is kept awake by a video some toys and baby friendly books while the tests are done Testing cannot be done if the child is asleep Sleep has various stages and most of them result in diminished or absent cortical re sponses relative to those that occur while we are awake just as we are generally less sensitive to sound when we are asleep Infants like to sleep and they go to sleep quickly Without EEG equipment and training it is difficult perhaps impossible to judge if they are lightly asleep or deeply asleep It is strongly recommended that the child be awake for the tests Suzy is encouraged to watch a silent cartoon on TV The video enter
37. nd to leave messy residue in the test en vironment Eating and drinking are excellent distracters Good choices include baby bottles or infant sipping cups and soft foods such as banana custard fruit gel or sultanas Avoid hard foods eg crunchy crackers or large pieces of food of that require a lot of chewing as the resulting noise and jaw movements can affect record ings Breastfeeding is good for calming infants but often can induce sleep If the baby must feed during the assessment watch very careful ly and rouse the child gently if they begin to doze off or appear their eyes start to appear unfocussed Be prepared to pause testing if the child s state becomes inappropriate Some times a short break to have a feed can gibe baby a boost to keep them going for a bit more test ing 23 O Avoid distraction activities that are too stimu lating or that encourage increased vocaliza tion for example physically vigorous play or games gestures that encourage the child to answer questions or name objects Parents may sometimes need some guidance about activities that are inappropriate in this respect If the child is content and quiet it can be best for the distracter to sit quietly or withdraw and leave them to their own devices If the child is unsettled sometimes it can help for the dis tracter to get right out of their view and let the parent try to settle the child before proceeding Try to end the t
38. nding on the clinic vis its should be done every 2 4 weeks 77 According to Harvey Dillon cortical tests are being positioned as a very informative evaluation tool rather than a fitting tool It is anticipated that further research and evaluation might show these measurements to be so useful that this approach will become a fitting tool rather than an evaluation tool For now clinicians should make their own decisions on adjusting amplification and what to do if HEARLab says there is no response even though residual EEG noise has been reduced to a level where a response ought to be visible if one is indeed present Early intervention is critical Early detection and treatment of hearing is critical Here is a quote from the NAL annual report New born hearing screening programs aim to diagnose hearing impaired infants within the first few weeks of life so that early intervention including the fit d ting of hearing aids can be provided before the age of six months This is important because it has been demonstrated that children diagnosed before the age of 6 months develop significantly better speech and language than those diagnosed after this pe riod Clearly appropriate amplification is a crucial factor Yoshinaga Itano et al 1998 What about adults The tests discussed above ACA can be used to evaluate hearing aid fittings on people of any age not just infants and babies Later we discuss h
39. nts the responsibility for the audiologist is still consider able The clinician must be experienced and be able to read results and understand them and ensure they tie in with other audiological findings They should also expect to get different results for each patient and be prepared to handle them accord ingly Suzy s Follow Up Visit After Suzy had worn her hearing aids for about a couple of months she was evaluated again with HEARLab as part of her periodic review Suzy had acclimated to wearing the hearing aids and the ini tial responses were good Now Dr Judy was con cerned about the gain in the lower frequencies Dr Judy had initially set the ave gain to 35 dB and the frequency response the slope to a 6 dB roll off This was done because Suzy s diagnostic hearing tests had indicated a moderate loss not a profound impairment There is a history of genetic hearing loss in Suzy s family so Dr Judy had wondered if Suzy had a cookie bite audiogram or a more tra ditional flat loss The slope of the frequency re sponse was initially selected to be rather cautious Dr Judy did not want to over amplify the lower frequencies in case Suzy happened to have good hearing in that zone During the follow up test Dr Judy noted that the low frequency cortical response to the m stimuli was unclear She increased the gain in the lower frequencies by 10 dB and the tests were repeated This adjustment produced
40. o tentials are made by external stimuli our test sig nals Evoked potentials are extracted from sets of recording by the digital averaging of epochs An epoch is a recoding period time locked to the re peated presentation of the test signal The spon taneous background EEG fluctuations which are random relatively to the point in time when the stimuli occurred are averaged out leaving the event related evoked brain potential These evoked electrical signals reflect only that activity which is consistently associated with the stimulus processing in a time locked way The evoked poten tial thus reflects with high temporal resolution the pat terns of neuronal activity evoked by a stimulus Our italics from Teplan same reference as preceding paragraph It is important to realize that while the averaging process reduces the level of noise arising from all sources other than neural circuits responding to the stimuli it never totally eliminates this noise HEARLab uses the variation between the individ ual epochs combined with the number of epochs included in the average to estimate the residual noise in the averaged response It displays this as a number in microVolts and also uses this value to control a set of traffic lights The lights go green when the residual noise is less than 3 4 microVolts NAL s research has shown that if the residual noise is less than 3 4 microVolts cortical responses from young chi
41. o or it curves upward slightly The intensity of these responses is sub dued i e much smaller than those seen with infants Infant CAEPs e Have a positive peak near 200 milliseconds The early peak and trough seen in adults are usually missing s The end of the curve the tail seen between 400 500 ms is decidedly negative curv ing lower on the graph This negativity is easier to see if you overlay adult and infant curves e The size of the response is robust a lot higher than an adult In normal hearing infants the overall shape mor phology amplitude and time at peak of the curves can change a little when different test signals are used These differences tell us that the cortex of little babies is mature enough to tell the differences between various speech sounds This is very excit ing because all speech and language development 16 depends on the differentiation abilities of the brain We want to adjust amplification to maximize these differences According to Suzanne Purdy CAEPs in infants evoked by some different speech phonemes differ in latency and morphology This indicated differ ent underlying neural representations of speech sounds and suggests that the information needed to differentiate the stimuli is available to the lis tener However this is really only reliable at the group level For the individual infant therefore a lack of difference between the waveforms for two diffe
42. onsiderable intra and inter subject vari ability is common e There has been a recent resurgence of inter est in clinical application of the response with computed evoked potential topogra phy techniques and sophistical stimulation e g speech stimuli Large evoked cortical responses are seen in in fants at about 200 milliseconds All speech sounds generate broadly similar CAEP responses Close inspection however indicates that the peak am plitudes and or latencies vary systematically for some speech sounds relative to others HEARLab indicates the probability that the response to each of the sounds m g and t is different from each other If any two of these responses are indi cated as different from each other for an individual patient then you can take this as an extra reassur ance that complex processes are underway in the child s brain in response to the speech sounds However there is no need for concern if the re sponses though present are not marked as differ ent from each other Normal hearing children can differentiate all the sounds of speech even though the cortical responses are often indistinguishable from each other Figure 2 and 3 from Suzanne Purdy show the average curves for adults and infants Notice the differences between the adult and infant curves It takes considerable time for an infant s brain to ma ture The early peak and trough seen in adult data become more apparent after t
43. ou see a good response one that has a high probability of detection The test time for 100 epochs is about two minutes If the patient is exces sively active this time will increase either because epochs are rejected or because accepted epochs contain more noise than when the child is in a quiet relaxed state If the patient you are testing will not stay still for the entire test try to get as much data as you can initially then you can try again to get the remain der of the data later For example if you are check ing a hearing aid fitting on a difficult to test patient you might use one speech sound and the corre sponding cortical response for your primary testing goal You gather data for this primary target quickly you can gather the rest of the data at a later time Later does not mean one month later it is possible to let the child nurse or take a short nap and continue testing when they wake or after they are fed If you get one highly reliable bit of excellent data you can often use this to insure you have a hearing aid fitting that is providing some benefit The sound field speaker is usually located near the patient 1 meter away directly in front of the in fant at 0 degrees A person who is distracting the child can sit on a little chair positioned so that the sound path from the speaker to the child s hearing aid microphone is not obstructed The opposite ear is occluded with the c
44. overly restrained For example try starting while an older infant is playing on the floor or at a child s table and chair DU Try not to physically stand over the child while doing skin preparation Working from behind the child may be a good option For your own health and safety try to maintain a pos ture that is ergonomic and doesn t place strain on your back or neck Sitting on the floor beside baby whilst chatting to Mom or Dad and gently rubbing the skin can be a very non threatening way to get the skin prepared DU Electrode sites are generally prepared by abrad ing with a cotton applicator bud and a medi cal gel intended for the purpose Rub firmly and vigorously enough to cause a slight red ness on the skin surface but not so hard that the child becomes obviously distressed by the sensation Rubbing gently but firmly back and forth works better than dabbing at the skin Rub on the back of Mom or Dad s hand first so they know what it feels like DU Work as quickly as possible and minimize the number of physical contacts with the child Don t fuss or overdo it but be mindful that it is better to prepare skin thoroughly than to have to repeat the whole process DU If the child needs reassurance about the prepa ration modeling the procedure eg by rubbing the forehead of the parent or a doll with a cot ton bud and sticking on an electrode can be helpful Try letting an older child ha
45. ow the cortical response changes as infants mature HEARLab also comes with CTE Cortical Thresh old Estimate which is used to estimate hearing thresholds Tonal test signals can be presented using insert earphones or a bone vibrator Insert earphones reduce the ambient noise and allows us to do hearing tests at lower intensity levels without hearing test chambers They are also more accepted by small children than are supra aural headphones and provide greater inter aural at tenuation thus reducing the need for masking Clinical audiologists see a wide variety of difficult to test patients Some patients have physical or emotional disabilities that prohibit them from co operating fully with a typical hearing test Other patients are highly motivated to have hearing loss for medical or legal reasons Cortical tests are ideal for difficult to test patients of any age where objective biologically based responses are need ed These tests are especially helpful for patients with exaggerated hearing loss or a patient involved in a medical legal disputes where objective data are needed for legal reasons For people with sen sorineural hearing loss cortical responses are usu ally visible within 10 dB of behavioral thresholds A Little Information about Brains If you have recent training in ABR you might want to skip this section Nerve cells neurons produce electrical signals throughout the body There a
46. pendix A Practical aspects of CAEP testing with infants The HEARLab system has been designed to make objective audiological assessment as easy and effi cient as possible However testing young children regardless of the hardware and software employed presents practical challenges The application of CAEPs to a pediatric population may be relatively new to mainstream clinical prac tice however the general techniques and strate gies used in other areas of pediatric audiology are still highly relevant Experienced clinicians will be well aware of how to best manage the test environ ment and will have developed many of their own solutions to overcoming the issues that inevitably arise when working with infants The clinical validation trials of the new HEARLab system involved repeated CAEP measures con ducted in a controlled and systematic way This provided a valuable opportunity to investigate dif ferent approaches and test techniques and to con sider their relative merits without the usual restric tions of a routine clinical assessment appointment in which a diagnostic outcome must be achieved within a limited time frame Some general suggestions based on observations made during the study are summarized in this Appendix It is hoped that this information may provide useful guidance particularly for clini cians with less experience in pediatric audiology or those who are new to using electrophysiological assessment
47. pore tape either on its own or with a headband is appropriate for keeping re usable type electrodes attached Once the electrodes are attached try to drape the leads behind the child avoiding contact with the child s face or neck If the child can feel them they will be more inclined to pull at them Try to keep the leads away from cloth ing eg don t let them become tangled in bibs or collars Loosely taping the leads to the back of the child s clothing using micropore tape may be helpful but ensure they are not taped so tightly that the electrode leads are pulled off the head if the child suddenly leans forward Make sure that if the parent is holding the child that the electrode leads are not cramped or pulled under the parent s arm Try directing the leads up and over the parent s shoulder Avoid the child leaning back onto the electrode leads or making sudden large movements such as lunging forward Strategic use of dis traction toys can help in this respect If the child starts to touch the leads or elec trodes don t over react eg grab suddenly at the child s hands In preference try to distract the child by offering them an alternative item to play with Once the electrodes are in place avoid touch ing them unless really necessary ie they are obviously slipping becoming unstuck Draw ing child s attention to them will often result in renewed efforts to remove them Don t let t
48. py done with the microscope and tympanomentry had been normal The ENT ruled out middle ear involvement North Shore Audiology gave John a second hearing test three months later and found about the same 65 85 dB hearing loss bilaterally for air conduction The bone conduction thresholds air bone gap ob served during the first hearing test disappeared on the second audiometric evaluation John and the audiologist talked about this John said maybe he was responding to the vibration not the sound North Shore Audiology was uncomfortable with this case and wanted cortical tests to see how ac curate the audiogram and hearing aid fitting were They referred John to Dr Judy Smith John coop erated with the test He had signed the release of information form and all other appropriate paper work Dr Judy talked with John He gave her a copy of his latest hearing test done by North Shore Audiology He said the hearing aids were working fine and he could hear well when he wore them Without the hearing aids he said he could not hear John had done his homework Dr Judy started the threshold CTE cortical threshold estimate tests with the Right ear using insert earphones She observed good cortical re sponses at 65 dB SPL she lowered the input level to 55 dB then 45 dB and good responses were ob served She switched ears Repeated the sequence Once again good responses were observed At this stage John was becoming
49. r follow up visits to monitor the changes in his hearing due to this conductive component Less gain will be needed as soon as the fluid clears out of his ears As Danny s testing with the hearing aid pro gressed a waveform that looked a bit like a cortical response was observed but the statistical calcula tor indicated that it was not significantly different from random noise Dr Judy stopped the test and increased the hearing aid gain by 10 dB Danny was hungry so his mother fed him a little while Dr Judy was adjusting the hearing aid The test was re started and everyone cheered when clear cortical responses with correspondingly high significance levels were observed When hearing aids are fitted to adults we spend a lot of time asking the patient How does it sound Is my voice a little too loud or a little too soft HEARLab give us the ability to present speech sig nals to infants and observe cortical responses that are highly correlated with perceived speech The tests are done with the hearing aid set to the audi ologist s recommended level If the desired cortical responses are observed the fitting is verified however the word verified should not be taken literally It is more accurate to say the fitting is in the right ballgame or a lev el has been found where the input signal actively stimulates the auditory cortex When cortical re sponses are observed we should not assume the h
50. re huge numbers of neurons in the brain When activated the neurons in the brain make a lot of electricity When a large group of neurons fire in synchrony they produce enough electricity that we can detect and record these responses using surface electrodes on the scalp 10 According to Teplan The human brain starts ma turing long before the baby is born and electrical activity is seen around 17 23 weeks of prenatal de velopment At birth the number of neurons is huge 10 to the 11th power Adults have about 500 tril lion synapses the brain can be divided into three sections cerebrum cerebellum and brain stem The cerebrum consists of the left and right hemisphere with a highly convoluted surface lay er called cerebral cortex The cortex is a dominant part of the central nervous system The cerebrum contains centers for movement initiation conscious awareness of sensation our italics complex analy sis and expression of emotions and behavior The cerebellum coordinates voluntary movement of muscles and balance maintaining The brain stem controls respiration heart regulation biorhythms neuro hormone and hormone secretion The high est influence to EEG comes from the electric activity of the cerebral cortex due to its surface position Our italics From M Teplan Fundamentals of EEG Measurement Measurement Science Review Vol 2 Section 2 2002 Evoked potentials also called event related p
51. refully Important Note If the gain output of the hearing aid is much too high you see typical cortical responses Nothing in the data tells you that you are over amplifying this person If the initial settings produce good quality cortical responses the patient s auditory neural system is responding to the amplification The test results do not tell you whether or not you are over amplify ing the patient Mindful of this fact Dr Judy Smith was cautious with the gain level for Suzy If you adjust the hearing aid to the prescribed gain level and you run a cortical ACA test with the hear ing aid on If the test conditions are good quiet the baby is awake and the cortical response is poor or absent You may need to review the hearing aid prescription the estimate of the hearing loss may be too low poor quality ABR results etc When the initial test did not produce a good cortical curve Dr Judy was prepared to increase the gain level for Danny because all of his hearing test data pointed to a profound mixed hearing loss Let s turn our attention to the family of the pa tient Dealing with the Family Suzy s father was especially problematic He is an example on how the HEARLab test results can help in counseling situations Suzy s father refuses to accept the fact that Suzy has a hearing loss and needs to wear hearing aids When Dr Judy realized the family was having p
52. rent speech sounds is no cause for alarm Different stimuli create different responses You can see this in Figure by comparing the highest curve on the chart the black line that represents t with the one peaking farthest to the right the green line that represents m Low mid and high pitched speech like sounds are included in the test to give us some indication regarding the infant s hearing in different frequency zones The p Value A statistical analysis of each response is automati cally calculated and displayed on the screen as the p value for each sound This is a sophisticated statistical test based on the Hotellings t2 statistic that helps the clinician determine the likelihood probability that the waveform observed was caused by the patient detecting the test signal This statistic runs and updates itself in real time Re search on this indicator has shown it to be very reliable often better than the clinician running the test Do not rely solely on this analysis The graphi cal display also shows the time region in which the peak should fall if the child s auditory system has been exposed to sound for all of his her life If the child spent significant time without adequate au ditory stimulation e g prior to receiving an effec tive hearing aid fitting or a cochlear implant then peak latencies longer than those in the shaded re gion may be observed This is normal for a child w
53. roblems she scheduled them for a counseling ses sion She used the cortical responses to show the father that Suzy had a hearing problem The con versation went something like this Suzy s brain can show us whether or not she is hearing Pointing to the cortical responses saved in Suzy s file Dr Judy said Look here is the re sponse Suzy s brain makes when she wears the hearing aids The neurons in her brain are telling us I can hear I can hear When we remove the hearing aids these responses disappear She can not hear When she wears the hearing aids she will hear well If we remove the hearing aids she will not hear and she will not learn to talk Her ability to learn depends on her ability to hear You need to help make sure she wears the hearing aids and they are working well The visual response produced by HEARLab helps parents see the result of the amplification It is very comforting to see that the amplification is work ing well If families are having trouble accepting that their child needs to wear amplification it can be very helpful to show them a graph that shows no brain responses to speech sounds without hear ing aids and good brain responses with hearing aids Let s return to our story about Danny HEARLab measurements can be done easily on a child that cooperates by being quiet Danny is a precious little baby who seems to like the TV when he is in the office Luckily toda
54. roduced when the child moves or cries creates a disturbance in the respons es and when this disturbance is large enough to be recognized by HEARLab as an unusual occurrence each epoch containing these high noise levels is omitted from the average Either way neuromus cular noise lengthens the measurement process In the first case a greater number of epochs must be averaged to reduce the noise down to low levels in the second case a greater number of stimuli must be presented so that the required number of epochs provide data that are accepted for processing Con sequently it is important that the child be comfort able and quiet when the tests are done When threshold prediction tests CTE are done the ambient floor noise in the room and the natu ral muscular noise of the child all become critical factors As you attempt to test at lower and lower levels all noise acoustic and neuromuscular be comes critically important Some infants like children with cerebral palsy are difficult or impossible to test because the noise generated by muscular contractions cannot be fac tored out from the test data Some medications pre scribed to special needs babies e g anti epileptic medicines may also interfere with the response Here are some practical suggestions on testing Note Lyndal Carter contributed many pages of practical suggestions to this document They are included in the appendix This following list wa
55. s abstracted from Suzanne Purdy et al Chapter Eight e The timing is very important The infant needs to be settled and awake If the infant is too active the recordings will take too long and contain too much muscle activity e Pause the tests when the infant gets too vo cal e Have everyone monitor the infant s state Infants fall asleep unexpectedly or can be close to sleep with their eyes open e Electrode applications need to be fast pain less and secure since the infant will be sit ting up awake on the caregiver s lap Tell the family not to use cream or hair con ditioner on the infant s head prior to com ing to the appointment as the electrodes can slide off Drape electrodes away from the face and hands so that they are less likely to be no ticed and pulled at by the infant Use a lanolin based cream or an adhesive remover wipe to assist in electrode removal as it is much more pleasant for the family if you don t upset baby by just pulling off the electrode sensor pads when the test is finished Make sure the hearing aids have new bat teries for the test You don t want a battery going dead during the test When is cortical testing done The overall process can be summarized as 1 screening 2 diagnosis 3 fitting 4 cortical eval uation 5 then long term follow up and fine tun ing 1 Many infants receive a mandatory hear ing screening at birth Children who fai
56. se Dr Judy was worried about over amplification Suzy s initial aided ACA cortical tests looked good Dr Judy extended the tests us ing a much lower gain setting Poor quality cortical responses were seen Dr Judy interprets this data to mean the auditory neural cortex system was not adequately stimulated at the lower gain setting It seems the amplified sound was below Suzy s audi tory threshold levels i e Suzy s neural system was not detecting the speech sound used for the test So she rejected the possibility of using significantly less gain When Dr Judy started Danny s test poor quality cortical responses were seen Dr Judy interpreted this data to mean the initial fitting was too weak so she increased the gain of the hearing aids Her judgment was confirmed when she saw good corti cal curves at the higher gain output settings All of us understand that high power hearing aids can be very harmful if fitted improperly HEARLab is an exciting new tool that helps you evaluate a hearing aid fitting taking into account the extra ef ficiency of a tiny baby s ear it is more efficient in the higher frequencies due to the smaller volume in the ear canal HEARLab also help us see whether or not the presence of middle ear fluid has attenu ated the amplified sound to a level below threshold Gain output can be indirectly managed using corti cal tests However please read the following note ca
57. speech sounds are audible detected This concept will become clearer as we continue our story of Suzy and Danny Now back to the kids Hours after Suzy and Danny were born they both failed their newborn hearing screenings They were referred to Dr Judy Smith a local audiologist Dr Judy obtained extensive histories She did ABRs otoacoustic emission tests OAEs tympanomen try and other tests on these little babies It was ob vious they both had noteworthy hearing loss and needed amplification so she made impressions for earmolds and scheduled them for a Pediatric Hear ing Aid Evaluation But now what If you are Dr Judy and you determine Suzy has a substantial hearing loss and Danny has a more profound hearing loss how do you determine the exact amount of gain each infant needs Do you put all of your faith in the target recommenda tions of NAL or DSL software Do you use the guidelines you learned in graduate school The most important question is How do you determine if the amplification levels you select for Suzy and Danny are correct Dr Judy needs a machine that can tell her whether or not Suzy and Danny are perceiving speech their neural systems are detecting speech sounds at appropriate levels after they are fitted with hearing aids We have great news With great excitement and pride Frye Electron ics in Oregon and The National Acoustic Labora tories NAL in Australia are pleased
58. tains her and helps to keep her qui et while the tests are done At times she becomes bored watching the TV so her father entertains her with her beloved teddy bear When that does not work dad uses a light up toy and a mirror Babies 4 love to look at themselves in the mirror Dr Judy has many distracters she uses to keep the babies entertained The child must be calm while the test is being done These distracters in clude Small bright colored soft toys and puppets Light up toys A TV showing a silent colorful cartoon Hand held mirrors A shiny sparkly ball on a string Some kids books with colorful pictures little babies love black white and red con trasting colors and pictures of other babies Squeeze toys that changes shape when you squeeze them Avoid the ones with squeak ers inside e Blowing party soap bubbles silent and fascinating to most babies Stores like Party City have a large supply of fun to look at and fun to play with toys Whirly light up toys that go round and round are great distracters during electrode placement They can be a little too noisy during testing When the sparkly ball on a string is used dad is told to not to move it around too much You don t want the child s eyes and head moving around ex cessively You want to keep muscle noise to a minimum Suzy is fitted with moderate gain hearing aids the left hearing aid fitting is arbitrari
59. techniques with young children Before the appointment L Prior to the appointment provide parents care giver with information written and verbal about the procedure This will reduce the time spent in explanation at the assessment DU When arranging the appointment ask about the child s routines Try to book the test at a time of day when the child is likely to be in a good mood and less likely to be overtired and irritable Allow plenty of time so that ap pointment is not rushed and it is possible to take breaks if needed DU Check whether the parent care giver intends to bring sibling s to the appointment If it is nec essary for siblings to attend make sure there will be suitable activities supervision away from the test room The parent should be free to focus their attention on the child having the test L Ask the parent care giver to bring food drinks or dummies pacifiers for the child to the appointment Some favorite toys that are suit able as quiet distracters can also be useful in making the child feel more secure in the test en vironment DVDs that the child enjoys can also provide familiarity and useful distraction L Suggest that the child be dressed for the as sessment in layers of clothing that can be easily removed Electrode contact can be comprised if the child becomes overheated and sweaty and it may be necessary to remove clothing to cool them down It is better not
60. to have to pull clothes over the child s head once they are wired up DU Ask parents care giver to ring and postpone the appointment if their child is unwell partic ularly if the child has a temperature A restless and irritable state is not conducive to quality recordings DU Call the parent care giver to confirm the ap pointment the day before and take the oppor tunity to check whether they have any ques tions or concerns they would like to discuss Test environment L Make the test environment child friendly For example decorate the test booth and surround ing areas using items such as mobiles displays of soft toys out of the child s reach and fabric motifs Avoid hard reflective objects that will cause sound reflections Minimize technical clutter Keep wires out of view and labora tory supplies in drawers Children particularly if they have undergone medical treatment or hospitalization in the past may associate such items with unpleasant procedures L Keep the test area clean and tidy A plastic backed Draped sheet available from medi cal suppliers is a useful surface for arranging preparation materials and for wrapping used electrodes cotton tips etc afterwards for dis posal 20 L Provide a chair that is as large enough for the child to sit comfortably either on their par ent s lap or beside them during testing Some children become irritable if they feel overly r
61. to introduce HEARLab a test instrument used to measure cor tical responses with and without hearing aids Currently there are two parts to HEARLab ACA Aided Cortical Assessment and CTE Cortical Threshold Estimate ACA is used to evaluate hearing aid fittings using real speech sounds presented through a speaker You view the evoked cortical responses of a tiny infant who is wearing hearing aids In this story we call ACA the aided tests It is more properly called NAL ACA National Acoustic Labs Aided Cortical Assessment a study of evoked cortical re sponses while hearing aids are worn CTE is used to estimate unaided hearing thresh olds Tones are presented via insert earphones or a bone vibrator The evoked cortical responses are studied In this paper we call CTE the threshold estimates or threshold tests We will discuss both ACA and CTE ACA Aided Cortical Assessment Dr Judy has many diagnostic tools at her disposal that she uses to evaluate the hearing ability of in fants But until now none of these tests could di rectly confirm whether or not the amplification was stimulating the auditory cortex Suzy and Danny are only a few weeks old and we cannot ask them Can you hear the sound of my voice In the past it was almost impossible to evaluate the appropri ateness of the amplification With HEARLab we now have a new tool that di rectly measures the infant s cortical responses so
62. ts Tiffany had been seen several times by a local pe diatrician Dr Sanchez who treated her for chronic otitis media with constant purulent drainage Dr Sanchez observed large perforations in both her ear drums Tiffany has been fitted with BTE hearing aids years before by another clinic but Tiffany refused to wear them Dr Sanchez referred Tiffany to Dr Judy Smith for a comprehensive evaluation Tiffany was a joy to work with and sat very quietly while Dr Judy did the tests Dr Judy started with the unaided ACA test and she was delighted to see good cortical responses without a hearing aid at 65 dB SPL Without question Tiffany had some hearing loss due her middle ear problems but her hearing was much better than reported Dr Judy switch to the CTE cortical estimate as sessment and she presented tones to Tiffany us ing the bone vibrator The responses were close to normal hearing levels This information was shared with e Dr Sanchez the Pediatrician who referred Tiffany to an ENT to manage the middle ear problem The foster family And Margaret the school audiologist who referred Tiffany to counseling It turns out that Tiffany was a severely abused child who lived in a shell All reports about her being deaf were inaccurate She needed consid erable time in counseling A year later her speech and language skills were improving Her ears are being closely monitored by t
63. uccess board and the many photographs of beautiful in fants There are three parts to HEARLab the comput er the stimulus controller box and the Electrode Processor box The computer Thirty years ago an ABR unit was expensive and had limited processing power Today s comput ers are a thousand times better Today s comput ers have more memory and a higher processing speed than main frame computers thirty years ago HEARLab presents sounds and records the tiny electrical signals produced in the brain while re ducing by averaging the background noise made by the brain Years ago you needed to spend a lot of money on a computer to do this Today it can be done with a normal computer A gig of RAM combined with the modern processing speed and huge storage abilities of computers gives us all the signal processing capabilities we need The HEARLab computer is a typical off the shelf computer It comes with the software installed One word of warning Do not be tempted to install any other software on this computer HEARLab is a dedicated computer designed for a single purpose The integrity of the system has to be pro tected so the processing capabilities can be main tained The software is designed to reject the in stallation of additional programs If you bypass these built in protections the system will crash and Frye will not furnish software support So please make sure that all peopl
64. uilt on the significant research done internationally on cortical responses and has in particular focused on how to make the test as au tomated as possible with as much interpretation as possible done automatically by the equipment NAL has published some of their research on this topic with more in the publication process Research particularly that by North American researchers Curtis Ponton and Anu Sharma has shown that cortical responses can tell us more than just whether or not the sound is perceived The latency of the positive peak in infants and young children is highly correlated with the amount of exposure to sound that the child has had For ba bies with normal hearing the latency decreases from over 200 ms at birth to around 120 ms by age 2 years Infants who do not receive adequate stimulation until receiving a hearing aid or cochlear implant at say 12 months of age initially have latency similar to that of a newborn baby Over the following year of exposure to sound the latency will decrease by the same amount that normally occurs during the first 12 months of life The latency of the ob served response thus tells us about the maturity of the processing system within the cortex maturity that can develop only in the presence of auditory stimulation HEARLab includes a graphical rep resentation of normal latency given the age of the child so that the maturity of the response of the individual child being measured
65. uncomfortable and he showed his irritation and he asked to end the tests Dr Judy told John that her test results were in consistent with the hearing tests he had received at North Shore Audiology She scheduled him for another visit He never returned for the follow up visit 17 Dr Judy sent North Shore Audiology a report that said in effect My current tests indicate marked in consistencies with your earlier hearing test on the basis of these tests we cannot estimate John s lev el of hearing loss however because we obtained good CAEPs at 45 dB SPL bilaterally unaided we believe his hearing is significantly better than the levels indicated by the behavioral audiogram North Shore Audiology forwarded Dr Judy results to all interested parties and waited for the results of the additional studies but John never showed up for these studies Tiffany Tiffany is a sweet very quiet six year old girl living in a foster care home She has been in several fos ter care families the last couple of years She is in a special education classroom at school She does not speak she responds when asked to do things by teachers and her foster parents The school audiol ogist Margaret gave her several hearing tests Tif fany s responses were inconsistent she responded at very high levels e g 100 dB HTL But Margaret the audiologist wrote on the hearing tests I don t trust these values We need additional tes
66. ve a turn at putting an electrode on a toy or on their par ent 21 Some children will be reassured by watching the preparation in a mirror but this may make others more apprehensive Television can be a good distraction during electrode placement Use a range of children s DVDs with lots of color and movement If the child becomes interested the DVD can be left playing with the sound muted when testing starts This is the time to use your noisy fun toys before the real testing begins Make sure you put these out of sight before you start Wherever possible have a trained distracter in addition to the parent to interact with the child during electrode placement as well as during testing Toys that involve some fine motor manipulation eg block stacking button pressing can help keep hands away from the electrode sites Cleaning skin with an isopropyl alcohol prep swab after abrading is sometimes recommend ed and may improve contact but it can make the electrode stick very firmly and make it dif ficult to remove It can also feel stingy try it on yourself if you don t believe this Prepa ration with an alcohol wipe is not needed and is not recommended for the delicate skin of in fants Optimizing and maintaining electrode contact L Use a liberal amount of electrode paste under the vertex electrode even if a disposable elec trode that already contains conductive gel is used If using d
67. y the TV has an al most hypnotic effect on him Tympanograms are obtained quickly The amplification is lowered as soon as the middle ear fluid is gone from Danny s tiny ears and the aided cortical tests are repeated to make sure he is still able to detect speech sounds with the lower gain settings Some children like Danny will need additional gain from the hearing aids when they go through periods of middle ear fluid HEARLab simplifies the decision making process Cortical tests confirm the adequacy of the levels provided by a hearing aid fitting HEARLab gives the audiologist a tool that can be used to study the needed gain We know through years of seeing children with middle ear fluid that the amount of a conductive hearing loss can vary anywhere from a small 5 10 dB loss to a large 35 45 dB loss Pneumo otos copy and tympanometric studies are used to diag nose middle ear fluid However it is impossible to accurately estimate the size of the conductive com ponent created by middle ear effusion without air and bone conduction measurements We have seen older children with middle ear fluid that have a 35 dB conductive hearing loss in the low frequencies on Monday and have normal hearing in two weeks when the fluid dissipates Hearing levels can change quickly when middle ear fluid is eliminated The tests done with HEAR Lab help to remove this complication The effect of middle ear function is factored into the tests

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