1. New Perspectives in Central Auditory Processing Disorder
Sharon Cameron
Harvey Dillon
National Acoustic Laboratories

2. Overview of Presentation
New perspectives on CAPD
Description of the LiSN-S
Research behind LiSN-S
LiSN-S and the traditional APD test battery
How to interpret LiSN-S results
Management options
Description of LiSN & Learn Auditory Training Software
LiSN & Learn Phase I and Phase II Clinicial Trial Results
LiSN Screening Test – Sensitivity and Specificity Study
LiSN-S “Prescribed Gain Amplifier” - HI Study Years
Question time

3. What is CAPD? For children with (C)APD…..
“….. internal distortions degrade the auditory signal so that top-down processing typically predominates in most listening situations, particularly those in which complex linguistic and cognitive demands are coupled with background noise”
Putter-Katz et al (2002)

4. Operations Required for Comprehension of Speech in Noise
The major functional deficit of APD is an ability to hear in background noise.
In children, such a deficit would present in an inability to comprehend speech in the classroom.
When investigating APD there are a number of operations that may be impacted that would affect comprehension.
The figure from Wingfield & Tun (2007) shows operations required for comprehension of speech at the word, sentence, and discourse levels as constrained by a limited capacity processing-resource system.
Although displayed sequentially, many of these operations are interactive, with information flowing in both directions.
Wingfield, A and Tun, P (2007). J Am Acad Audiol 18:548–558

5. Source Discrimination aka Auditory Stream Segregation
The ability of the brain to tease apart all the sounds that arrive simultaneously at the ears and to form meaningful representations of the incoming acoustic information
Auditory cues such as the location of the sound, or the pitch of a speaker’s voice, help us to segregating the total stream of sound into its original sources
Auditory stream segregation is an important ability for attending to a target in background noise.

6. LiSN-S Development
LiSN-S was developed specifically to assess how children use:
Spatial location cues (ITD, IID)
Pitch differences between voices
to separate target auditory stimuli from distracting auditory stimuli that arrive simultaneously at the ears

7. LiSN-S Research – Spatial Processing Disorder
Noise
Noise
Speech
Noise
Previous research at NAL has shown that a number of children with suspected APD have difficulty separating sounds that arrive simultaneously at the ears from different locations.
Tendency to affect children with history of COM.
Deficit likely related to ability to use binaural (ITD; IID) cues
Noise

8. Description Adaptive speech-in-noise-test
Target sentences - 0º azimuth initially at 62dB SPL
Competing speech - 0º or ±90º azimuth at 55dB SPL
3-D auditory environment under headphones
Offers alternative to free-field testing
No special hardware required
Four LiSN-S conditions

9. LISN-S Conditions Low Cue SRT - SV0º DV0° Talker Advantage
Spatial Advantage
Total Advantage
SV 90°
High Cue SRT – DV90º
The use of difference scores to measure performance on the LISN-S minimizes the influence of top-down processing abilities such as linguistic skills on test performance.
For example, as linguistic skills affect both the SRT when the distracters are presented at 0°, and the SRT when they are spatially separated at ±90°, these skills will have minimal effect on the difference between the SRTs in these two conditions.

10. LiSN-S SRT & Advantage Measures
The use of difference scores to measure performance on the LISN-S minimizes the influence of top-down processing abilities such as linguistic skills on test performance.
For example, as linguistic skills affect both the SRT when the distracters are presented at 0°, and the SRT when they are spatially separated at ±90°, these skills will have minimal effect on the difference between the SRTs in these two conditions.

11. Client Screen

12. Configure Language

13. Client Session

14. Diagnostic Screen

15. Results Screen

16. Explanation Screen

17. Client Assessment Report

18. NA LiSN-S Sentence Equivalence Study
n = 24 Children recruited from University of Cincinnati
Age range 8 years, 3 months to 10 years, 0 months.
Same Voice 0º condition
30 sentences to establish SRT (eSRT)
Further 150 sentences presented:
50 at eSRT;
50 at +2dB;
50 at -2dB
Psychometric functions fitted
120 sentences adjusted in dB for equal intelligibility
Intelligibility increases 18.7% per 1dB increase in SNR

19. NA LiSN-S Sentence Equivalence Study

20. Australian LiSN-S Normative Data
202 participants:
106 children - 6 yrs, 2 mths to 17 yrs, 7 mths
60 young adults - 18 yrs, 1 mth to 29 yrs, 10 mths
36 older adults – 31 yrs, 8 mths to 60 yrs, 7 mths
English as a first language;
no history of hearing disorders;
no learning or attention disorders;
normal pure tone audiogram and middle ear function.

21. Low Cue SRT Better Low Cue SRT vs Age Group p < 0.000001
The graphs I’m about to present show the data for first 122 adolescent and adult participants combined with the child data.
On the graph shown here, age group is on the x axis and low cue SRT in dB is on the y-axis. As low cue SRT represents a SNR, the lower the score the better the performance.
In this condition the participant hears all the same speaker from the same direction, thus they do not have access to either spatial or pitch cues, and strongly rely on SNR.
ANOVA revealed a significant difference does exist between the groups on low cue SRT.
You can see that performance in the low cue condition improves with age and then plateaus once adult like performance is reached.
However, there is a slight – but not significant – decrease in performance after about age 50.
Planned comparisons revealed that adult-like performance on the low cue SRT measure was achieved by years of age. This is demonstrated on the graph by the dotted blue line.

22. High Cue SRT
Better
High Cue SRT vs. Age Group
p <
Moving on to the high cue SRT, this condition provides participants with both spatial and pitch cues to differentiate the target sentences from the distracter voices.
ANOVA showed that a significant difference does exist between the groups.
You can once again see that performance improves with age and then begins to plateau. However, like low-cue SRT performance starts to decline slightly –but not significantly – at about age 50
Planned comparisons revealed adult like performance was achieved by years of age for high cue SRT as well.

23. Talker Advantage Better
Talker Advantage vs. Age Group
p <
Better
Talker advantage is calculated as the difference in dB between the same voice 0 degrees (or low cue SRT) and different voices 0 degrees conditions.
As talker advantage is a difference score, the higher the score in dB shown on the y axis, the better the performance.
We again found that a significance difference between the age groups does exist.
Adult like performance on the talker advantage measure is reached at years of age. This suggests that up to this point children are still developing the ability to use pitch cues to differentiate speech streams.
Unlike the low and high cue SRT measures, talker advantage does not deteriorate in adults aged over 50 years.

24. Spatial Advantage Better
vs Age Group
p = 00005
Better
This graph shows performance on the spatial advantage measure.
Spatial advantage is calculated as the difference between the low-cue SRT and SV90 condition.
Adult like performance on the spatial advantage measure is achieved earlier than on talker advantage. Children are able to use ITD and IID as well as adults by about 11 years of age.
Again, there is no decline in spatial processing ability in older adults.

25. Total Advantage Better
Total Advantage vs
Age Group
p = 0.003
Better
Total advantage is calculated as the difference between the low-cue SRT and high cue SRT condition.
Like spatial advantage, performance on the total advantage measure plateaus at about 10 years of age, despite the fact that the ability to use pitch cues does not reach adult-like levels until about 14 years of age.
This would suggest that the ability to use spatial cues is the dominant factor employed by younger children when confronted with the task of processing speech in noisy environments.
Also, given the fact that there is only a 1.3 dB difference between mean spatial advantage and mean total advantage across age groups, it appears that the reliance on spatial cues to differentiate speech in noise continues into adulthood.

26. Conclusions
LiSN-S SRT scores show that the ability to understand speech in noisy environments develops with age, is adult like by 14 years and starts to decline by 50 years of age.
LiSN-S advantage measures show that ability to use spatial and pitch cues does not decline once adult-like performance is reached.
The ability to use spatial cues matures well before the ability to use pitch cues and thus plays a greater role in how well children, in particular, are able to hear speech in noise.
Low cue SRT shows a slight (but not significant) decline in performance from about age 40. As there are no pitch or spatial cues present in the stimuli in this condition the listener solely relies on SNR and perhaps other more top-down processes such as auditory closure, to differentiate the target from the distracters. Also, we know from the spatial, talker and total advantage measure normative data that the ability to use pitch and spatial cues remains constant as age increases. This indicates that the slight decline on the low and high cue SRT measures may be related to a decline in global processes, or perhaps auditory processing speed.

27. LiSN-S Cut-Off Scores
Level below which performance on a LiSN-S measure is considered outside normal limits.
Two and three-part regression equations fitted to account for improvement with age.
Low and High Cue SRT:
max (intercept + B-value * age, max (c, d + e * age) +
(2 * SDs of the residuals from the age-corrected trend lines)
Talker, Spatial and Total Advantage:
min (intercept + B-value * age, c) –
A correction factor is required for the High Cue SRT and Total Advantage measures.
The correction factor accounts for the effect on performance in dB of a change of presentation order from that used to collect the normative data to the presentation order used clinically.
The presentation order for each condition was counterbalance when the normative data was collected. E.g, the DV90 condition was presented either 1st, 2nd, 3rd or 4th.
However, whereas the DV90 condition was presented first only 25% of the time in the normative data study, it is always presented first clinically.
A regression analysis was conducted with presentation order (1, 2, 3 or 4) as the dependent variable and SRT for each condition as the independent variable.
An adjustment is calculated as the number of steps away from the order midpoint (2.5) multiplied by the B-value from the regression equation.
No adjustments were necessary for the SV0, SV90 and DV0 conditions, thus the low cue SRT, talker advantage and spatial advantage measures are unaffected.
However, an adjust of 0.9 dB was required to account for the change of presentation order on performance in the DV90 condition, affecting the high cue SRT and total advantage measures.  

28. Cut-off Scores - Low Cue SRT
Low Cue SRT:   max ( * age, -1.61) + (2 * 0.96)

29. Cut-off Scores - High Cue SRT
Low Cue SRT:   max ( * age, -1.61) + (2 * 0.96)

30. Cut-off Scores – Talker Advantage
Low Cue SRT:   max ( * age, -1.61) + (2 * 0.96)

31. Cut-off Scores – Spatial Advantage
Low Cue SRT:   max ( * age, -1.61) + (2 * 0.96)

32. Cut-off Scores – Total Advantage
Low Cue SRT:   max ( * age, -1.61) + (2 * 0.96)

33. LiSN-S Test-Retest Reliability
85 participants recruited from NA LiSN-S normative data studies.
Retested on LiSN-S between 1 and 4 months after initial testing (average 2 months, 2 weeks).
Mean test-retest difference ranged from 0.05 dB to 0.5 dB.
RM ANOVA revealed no significant difference between test and retest (p = to 0.974, age categorical variable).
Correlation between test and retest significant for all measures (p = to < ; r ranged from 0.3 to 0.6)

34. Spatial Advantage

35. NA LiSN-S Critical Difference Scores
Condition
Correction Factor (Mean Test-Retest Difference)
SD of the Mean Test-Retest Difference 
1.64 x SD
Critical Difference (Including Correction) dB
Low-Cue SRT
-0.49
1.51
2.47
-3.0
High-Cue SRT
-0.44
2.40
3.93
-4.4
Talker Advantage
0.31
2.46
4.03
4.3
Spatial Advantage
-0.05
2.21
3.63
3.6
Total Advantage
0.06
2.35
3.85
3.9
The CDSs represent the correction factor to be used when retesting a client on the LiSN-S after some period of remediation or compensation. 
CDSs allow the clinician to determine if a genuine improvement on the LiSN-S has occurred, taking into account practice effects and day-to-day fluctuations in performance.

36. Australian LiSN-S APD Study
Nine children aged 6 to 11 years experiencing listening difficulties in class relative to peers who had no learning or attention disorder (SusAPD group).
Eleven children with confirmed learning or attention disorders (LD group).
Assessed on LISN-S and results compared to 70 age- matched controls.
Assessed with a traditional (C)APD test battery

37. LiSN-S vs. Traditional Battery (LD Group)
Cameron & Dillon (2008)

38. LiSN-S vs. Traditional Battery – SusAPD Group
Cameron & Dillon (2008)

39. Low Cue SRT
Better
(LD)
To evaluate the significance of the pairwise differences between groups the Mann-Whitney U test (a non-parametric test of independent samples), was applied.
Control vs. LD: p = 0.879
Control vs. SuSAPD: p = 0.883
SusAPD vs. LD: p = 0.824

40. Spatial Advantage Better Control vs. LD: p = 0.983
Control vs. SusCAPD: p < *
SusCAPD vs. LD: p = *

41. LiSN-S Results – Normal
Male, 11 years, 10 months showing Normal Performance
Referred by educational psychologist for assessment.
WISC-V showed non-verbal learning disorder and also assessed as having Attention Deficit Disorder.

42. LiSN-S Results - SPD
Male, 7 years, 5 months with Spatial Processing Deficit
Referred for assessment on the recommendation of his class teacher to rule out an auditory stream segregation deficit as contributing to learning and language processing deficits.
The Kaufman Brief Intelligent Test – Second Edition (KBIT-2) reported Verbal IQ in the low-average range (13th percentile) and performance IQ in the average range (30th percentile).
The Children’s Auditory Performance Scale (CHAPS) completed by his teacher ratings listening in noise as -12 (fail) compared to -6 (pass) for listening in quiet.

43. LiSN-S Results – Memory Deficit
Male, 8 years, 3 months with Memory Deficit
WISC-V scores average across subtests.
Clinical Evaluation of Language Fundamentals – Fourth Edition (CELF-4) subtests all in average range except for Recalling Sentences, which was in the 5th percentile or borderline range.

44. LiSN-S Results – Attention Issues
Female, 7 years, 10 months with Attention Issues
Functional deficit of difficulty with reading and mathematics.
Average score across WISC-IV subtests.
School counsellor‘s report noted history of being easily distracted.
Very large variation in SNR on DV0 condition. Mind wandering.

45. Goal of Management Strategies
The ultimate goal of CAPD management in children is “… to maximize the auditory learning abilities so that communication and classroom learning experiences are more successful” Putter-Katz et al (2002)
Putter-Katz et al (2002). Seminars in Hearing, 23 (4).
Environmental modifications.
Cognitive processing, or “top-down” approaches use knowledge and experiences within the world to interpret acoustic stimuli.
Sensory processing, or “bottom-up approaches” focus on accurately receiving and transferring the acoustic aspects of the signal (such as frequency, duration, intensity) as it moves from the peripheral auditory system through the CANS to the upper cortex.

46. Managing Spatial Hearing Deficits
Teacher-directed strategies
Child-directed strategies
Language training
Classroom modification (+10 dB SNR)
Assistive listening device
Training in source discrimination
Teacher directed strategies:
monitoring and gaining attention
providing visual cues
pre-teaching new information
Child-directed strategies:
recognize and find a solution to difficult listening situations
whole-body listening techniques
Language training:
auditory closure training
vocabulary building
Classroom modification:
Carpet on floor; cloth poster boards on walls.
Preferential seating
SNR in occupied room should be +15 dB for all students and staff to have full auditory access to the spoken message. Typical classroom SNRs range from +4 to -7 dB. For this reason an assistive listening device can be helpful.
ALD is a very good option for children with a spatial hearing deficit, as the predominant problem in poor SNR.
A child with a spatial stream segregation deficit can get 50% of words correct on the LISN-S like everyone else – they just need a higher SNR to do it.

47. Auditory Training Research
Develop deficit-specific remediation for children with a spatial processing deficit.
Trains children to use binaural cues – i.e. differences in the timing and intensity of signals arriving at the ears from various locations - to attend to a target stimulus and filter distracting auditory signals.
Used in the home (as well as schools/clinics).
Provides detailed analysis, reporting and feedback.
Alternative/adjunct to ALD’s and other management strategies.

48. Description of LISN & Learn
Four games presented on PC over headphones
Target sentences at 0º azimuth (initially 62 dB SPL)
Competing stories at ±90º azimuth (55 dB SPL)
Weighted up-down adaptive procedure used to adjust the signal level of the target
SRT calculated over 40 sentences
131,220 unique sentences can be generated
A weighted up-down adaptive procedure is used to adjust the signal level of the target based on participant’s response:
decreased by 1.5 dB when target correctly identified
increased by 2.5 dB if wrong target identified
increased by 1.5 dB if the “unsure” response is made

49. LISN & Learn Game Target at 0˚: The horse kicked six wet shoes
Distracters at + and -90˚:
Tamsin’s Blanket (-90˚)
Eric’s Alarm Clock (+90˚)

50. Target: The horse kicked six wet shoes

51. Method 9 children (6 to 11 years) - LISN-S SA >2SD TOVA-A
TAPS-3 memory sub-tests
CAPD Pediatric SSQ
LISN & Learn - 15 minutes per day; 5 days per week; over 12 weeks (120 games)
Re-evaluate post-training; 3 months post-training

52. LiSN & Learn - Performance Over Time (n=9)
Better
10 dB
It is hypothesized that there is a greater deficit on the LiSN & Learn at the commencement of training (i.e. a greater improvement over time compared with the LiSN-S) because performing the LiSN & Learn requires a greater cognitive load than the LiSN-S (i.e. visual recognition, memory) and these abilities stabilize over time. This difference in performance (compared to normally hearing controls) between the LiSN & Learn and LiSN-S is similar to that seen between the LiSN-CD and LiSN-S.
LiSN & Learn SRT (dB)
Game Number

53. LiSN-S Results – Pre vs. Post (n=9)
LC SRT p = 0.158
Talker Advantage - p = 0.981
HC SRT p =
Spatial Advantage - p =
Total Advantage - p = 0.001
Vertical bars denote 0.95 confidence intervals
F(8, 64)=5.3847, p=.00003

54. Additional Results – Pre- vs. Post Training
CAPD SSQ:
Listening in Quiet – p = 0.103
Listening in Noise – p =
TOVA-A
Omissions – p = 0.168
Commissions – p =
TAPS-3
Memory Index – p = 0.003

55. Conclusion
LiSN & Learn training has the potential to strengthen or reorganize connections dedicated to binaural processing.
Training results in enhanced ability to process speech in background noise.

56. Method – Phase II Clinical Study
20 children - LISN-S spatial advantage >2SD from mean
10 x LiSN & Learn (experimental group)
10 x Earobics (control group)
Questionnaire
Participant (LIFE)
Parent (Fishers)
Teacher (LIFE)
LiSN & Learn or Earobics training – 15 minutes per day
Re-evaluate LiSN-S and questionnaires post-training
Offer LiSN & Learn to control group.
SSQ = Speech, Spatial and Qualities of Hearing Scale
LISN-S one-sided critical difference was calculated as (Mean Test-Retest Difference) - (1.64 x SD of Mean Test-Retest Difference).
This represents the decrease in dB needed to infer that there has been a genuine improvement in auditory performance on retest, taking into account mean practice effects and day-to-day fluctuations in performance.
Mean difference between test and retest was 0.5 dB for Low-cue SRT, 1.1 dB for High-cue SRT, 0.9 dB for talker advantage, 0.1 dB for spatial advantage, and 0.7 for total advantage.
A critical difference on the spatial advantage measure is 2.8 dB, and on the Low-cue SRT it is 2.5 dB 56 56

57. Phase II Study - LiSN & Learn Group (n=1)
SD from Mean
Pre-training
Post-training

58. Phase II Study - Earobics Group (n=1)
SD from Mean
Pre-training
Post-training

59. LiSN-S Screening Test
Develop screening test to be used by teachers, speech pathologist, psychologists.
Fully-automated instructional, testing, scoring and reporting functions.
Accessible via internet.
End-users own computer and headphones used.
Aims to:
Decrease time taken to refer children (and adults) with suspected CAPD for diagnostic testing with LiSN-S.
Reduce inappropriate referrals.
Reduced referral time will result in speedier implementation of management and remediation programs for those with SPD.

60. LiSN Screening Test Client data End-user inputs client data
Sound check
Sets output level of computer soundcard
Reference tone consists of “pulsed” speech-shaped broadband noise
Reference tone is presented at 40 dB below level of combined distracters
Listener adjusts volume control until he or she can “just hear” the reference tone
Assumed to be at least 10 dB SPL
Therefore level of distracters presented during test is approx 50 dB SPL

61. LiSN Screening Test Word familiarization task (in quiet)
3 target words (red, blue, green)
12 “foils” (e.g. hat, doll, milk)
Listener clicks on picture that matches word until all words correctly identified.
LiSN Screening Test
Distracters – looped stories (DV +/- 90º)
Targets and foils:
Female 1 at 0º
initially presented at SNR of +4 dB
2 second ISI
Listener clicks mouse when target heard.
Adaptive procedure used to find SRT that yields 50% intelligibility.
Level of word stimuli adjusted in 3 dB steps.
At least 6 targets presented as practice.
SRT calculated over up to 40 scored targets

62. LiSN-S Screening Test Studies
Target Stimulus Equalization Study
30 adults aged 18 to 29 years
SRT of scored target words (red, blue, green) consolidated across participants and psychometric functions formulated
Amplitude of target words adjusted for equal intelligibility
Sensitivity and Specificity Study
40 children and adults with suspected CAPD
Tested with LiSN Screening Test at referring centre
Tested with LiSN-S no more than 3 weeks later at NAL
Correlation between LiSN Screening Test and LiSN-S determined
ROC analysis used to determine sensitivity and specificity
Optimum criteria cut-off scores determined
SSQ = Speech, Spatial and Qualities of Hearing Scale
LISN-S one-sided critical difference was calculated as (Mean Test-Retest Difference) - (1.64 x SD of Mean Test-Retest Difference).
This represents the decrease in dB needed to infer that there has been a genuine improvement in auditory performance on retest, taking into account mean practice effects and day-to-day fluctuations in performance.
Mean difference between test and retest was 0.5 dB for Low-cue SRT, 1.1 dB for High-cue SRT, 0.9 dB for talker advantage, 0.1 dB for spatial advantage, and 0.7 for total advantage.
A critical difference on the spatial advantage measure is 2.8 dB, and on the Low-cue SRT it is 2.5 dB 62

63. LiSN-S Prescribed Gain Amplifier

64. CAPD and Hearing Impairment Studies
LiSN-S Study
160 participants (40 x 6-17; 20 x 18-29; 20 x 30-59; 80 x 60+)
Confirmed mild-to-moderately-severe SNHL (3FAHL of 65 dB)
Assessment gools:
LiSN-S + PGA
LIFE Questionnaire (6-17 years)
SSQ Questionnaire ( years)
COGNISTAT (60+ years)
“LiSN & Learn” Study
60 participants (10 x 6-17; 10 x 18-60; 10 x 60+)
Assessment tools:
Memory Test
“LiSN & Learn” + PGA (120 games) then re-assess
SSQ = Speech, Spatial and Qualities of Hearing Scale
LISN-S one-sided critical difference was calculated as (Mean Test-Retest Difference) - (1.64 x SD of Mean Test-Retest Difference).
This represents the decrease in dB needed to infer that there has been a genuine improvement in auditory performance on retest, taking into account mean practice effects and day-to-day fluctuations in performance.
Mean difference between test and retest was 0.5 dB for Low-cue SRT, 1.1 dB for High-cue SRT, 0.9 dB for talker advantage, 0.1 dB for spatial advantage, and 0.7 for total advantage.
A critical difference on the spatial advantage measure is 2.8 dB, and on the Low-cue SRT it is 2.5 dB 64

65. References
Brown, D., Cameron, S. Martin, J., Watson, C., & Dillon, H. (in press). The North American Listening in Spatialized Noise – Sentences Test (NA LiSN-S): Normative data and test-retest reliability studies for adolescents and young adults.
Cameron ,S., Brown, D., Keith, R., Martin, J., Watson, C., & Dillon, H. (2009). Development of the North American Listening in Spatialized Noise - Sentences Test (NA LISN-S): Sentence equivalence, normative data and test-retest reliability studies. Journal of the American Academy of Audiology, 20(2),
Cameron, S. & Dillon H. (2009) Listening in Spatialized Noise – Sentences test (LISN-S) (Version 1.013) [Computer software]. Murten, Switzerland: Phonak Communications AG.
Cameron, S. & Dillon, H. (2008). The Listening in Spatialized Noise – Sentences Test: Comparison to prototype LISN test and results from children with either a suspected (central) auditory processing disorder of a confirmed language disorder. Journal of the American Academy of Audiology, 19(5),
Cameron, S. & Dillon, H. (2008). Spatial hearing deficits as a major cause of auditory processing disorders: Diagnosis with the LISN-S and management options. In R. Seewald & J. Bamford, eds. A Sound Foundation Through Early Amplification Proceedings of the Fourth International Conference: Phonak AG, Switzerland,
Cameron, S. & Dillon, H. (2007). Development of the Listening in Spatialized Noise - Sentences Test (LISN-S). Ear and Hearing, 28(2),
Cameron, S. & Dillon, H. (2007). The Listening in Spatialized Noise - Sentences Test (LISN-S): Test-retest reliability study. International Journal of Audiology, 46,

66. Acknowledgements and Q&A
Dr Harvey Dillon
Director of Research
National Acoustic Laboratories
Helen Glyde
Research Audiologist