1. National Acoustic Laboratories Cooperative Research Centre for Hearing *Speech Science, The University of Auckland, New Zealand *Speech Science, The University of Auckland, New Zealand ** Audiology, Macquarie University The application of cortical auditory evoked potential recordings in infant hearing aid fitting Maryanne Golding, Harvey Dillon, Suzanne C Purdy*, John Seymour, Wendy Pearce, Lyndal Carter, Richard Katsch, Mridula Sharma* *, Katrina Agung, Kirsty Gardner-Berry

2. Evaluation of aided functioning in infants Universal new born screening Early fitting of hearing aids Need for an evaluation method Confirmation of fitting Fine-tuning needed Cochlear implant needed

3. So baby, how does it sound? Objective hearing aid evaluation for: young infantsyoung infants difficult-to-test peopledifficult-to-test people

4. Why the rush? Language ability 6 months after implantation

5. Why use cortical responses?

6. Why cortical responses to evaluate hearing aid fitting in infants? Reliably present in awake young infantsReliably present in awake young infants More likely to correlate well with perceptionMore likely to correlate well with perception Can be elicited by a range of speech phonemes – close to desired outcomesCan be elicited by a range of speech phonemes – close to desired outcomes Stimuli handled reasonably by hearing aidsStimuli handled reasonably by hearing aids Can be very frequency specific if neededCan be very frequency specific if needed

7. Where do cortical responses come from?

8. The end of the road

9. Auditory cortex and current sources Sussman et al (2008)

10. Cortical responses in adults with normal hearing

11. Adult 2.5 5.0 300.0400.0 µV 0.0100.0200.0500.0600.0 0.0 -2.5 P2 N1 P1

12. Adult grand mean waveforms at Cz Tones Speech

13. Cortical responses in infants

14. Infants ms 500.0600.0300.0400.0100.0200.0-100.00.0 µV 0.0 5.0 10.0 15.0 -5.0 P N

15. Maturational effects on cortical evoked response morphology Ponton et al (2000) N=8-16 per grand meanN=8-16 per grand mean Cz siteCz site stimulus = 10 click train, 2 ms ISI @ 65 dB SLstimulus = 10 click train, 2 ms ISI @ 65 dB SL rate = 1.3/srate = 1.3/s

16. 2 years12 years Cell bodies Cell bodies Axonal neuro- filaments Axonal neuro- filaments  Fewer neuro-filaments in young children, especially in more superficial cortical layers thought to generate N1 (Ponton, Moore & Eggermont 1999)  I III IV V VI II

17. Latency versus age Sharma et al NAL data

18. NAL Aided hearing impaired Infants and children (not all have P1) Children with CI (Sharma,2002) and NAL aided hearing impaired infants/children (N=40) using speech stimuli presented at 65 dB SPL.

19. Maturation with time “in sound” Ponton and Eggermont 2007

20. Auditory system maturity Ponton and Eggermont (2007): Latency matures consistent with the time “in sound” Sharma (2002): Provided implantation occurs by 4 years of age

21. Cortical responses in infants to different speech sounds

22. Grand Average n = 16 infants + MM OO OR UU AH EE SH SS ms 0.00200.00 400.00600.00 -

23. aheemmooorshssuu ah7477121213 ee7681112109 mm468810107 oo7887131013 or7118712107 sh1212101312314 ss1210101010311 uu13971371411 Number of subjects (out of 20) with significant differences between responses

24. Number of infants (N=20) with significantly different cortical responses to pairs of stimuli Based on MANOVA at Cz, 101 to 500 ms post-onset, in eight bins each 50 ms m vs t m vs g t vs g

25. Three stimuli m g t

26. Why not obligatory cortical responses? variable shape across agesvariable shape across ages variable shape with auditory experiencevariable shape with auditory experience variable shape from person to personvariable shape from person to person variable shape from time to time (state of person, especially sleepiness)variable shape from time to time (state of person, especially sleepiness) stimulusstimulus Inter-stimulus intervalInter-stimulus interval high skill level needed to read responses An automated method of response detection and response differentiation

27. Automatic detection of cortical responses

28. Desirable characteristics No reliance on a templateNo reliance on a template Able to use information from contributing portions of waveformAble to use information from contributing portions of waveform Able to discount non-contributing portions of waveformAble to discount non-contributing portions of waveform Hotellings T 2

29. Analysis using Hotellings t 2 statistic Divide each record into 50 ms time binsDivide each record into 50 ms time bins Average data points within each time bin Average data points within each time bin Use these averages as variables in Hotellings t 2 analysis Use these averages as variables in Hotellings t 2 analysis Result is probability of the waveform being random noise Result is probability of the waveform being random noise Time Voltage X = a 1 X 1 + a 2 X 2 +........ + a 9 X 9 Test: is there any set of weighting coefficients for which X ≠ 0? X3X3

30. Presentation of average response in series

31. Receiver Operating Characteristics – Expert judges 1 - Specificity Sensitivity d’

32. d’ results - for 60 stimuli For hit rate of 80% and false alarm rate of 5%, d’=2.5

33. d’ results - for 200 stimuli

34. Infants: Hotellings versus experts Normal hearing infants aged 7 to 16 months adults

35. Growth of amplitude with SL adults; tonal stimuli

36. Loudness growth above threshold Hellman & Meiselman, 1990

37. Detectability (adults; tonal stimuli) P=0.05 P=0.01 P=0.001

38. Significant responses – normal hearing and hearing impaired Adults; tonal stimuli (n=100 or 200)

39. Proportion with responses present - adults

40. …….. but infants move around !

41. Residual noise level rms noise = standard deviation / √n

42. Residual noise levels (for 100 epochs) 0 5 Adults Awake infants

43. Proportion with responses present (p<0.05) – normal hearing infants; 100 epochs

44. Cortical responses and functional performance Do cortical responses tell us about real-life auditory performance?

45. Parents are asked to describe their baby’s aural/oral skills based on real-life experiences (listening in quiet and in noise and alertness to environmental sound) Scores are assigned based on the number of observed behaviors and how frequently these occur. Final overall score of 0 – 40 can be calculated (and reported as a percentage). Parent’s Evaluation of Aural/oral performance in Children (PEACH) Questionnaire

46. Functional deficit versus cortical score * All aided children r s =0.60; n=24; p = 0.001 * SN only r s =0.61; n=12; p = 0.02 * MD only r s =0.82, n=5; p = 0.04 * AN only r s =0.36; N=7; p = 0.22

47. Reducing measurement variability (random electrical signals)  Speeding up measurements  Increasing validity of interpretation

48. Active electrodes

49. Capacitive Coupling 50 Hz Passive Electrodes

50. Capacitive Coupling 50 Hz Active Electrodes

51. Capacitive Coupling 50 Hz Passive Electrodes Active Electrodes

52. Finding thresholds with cortical responses What does an absent cortical response mean?

53. Cortical auditory evoked responses traditionally used for objective assessment of hearing thresholds in adults In 1965 Hallowell Davis showed good agreement between cortical and pure tone thresholds in childrenIn 1965 Hallowell Davis showed good agreement between cortical and pure tone thresholds in children For many years cortical response audiometry has been regarded as the “gold standard” for objective electrophysiological hearing assessmentFor many years cortical response audiometry has been regarded as the “gold standard” for objective electrophysiological hearing assessment

54. Davis (1965) Cortical evoked potential versus behavioural thresholds

55. From: Rickards, F. et al (1996) Cortical Evoked Response Audiometry in noise induced hearing loss claims. Aust. J. Otol. 2 (3)

56. Clinical applications and implications

57. Clinical applications of corticals For finding thresholds (when awake)For finding thresholds (when awake) Determining whether speech sounds are audibleDetermining whether speech sounds are audible –aided or unaided –for patients who can’t respond reliably by behavioral testing e.g., infants, multiply disabled people.

58. Clinical implications of corticals Significant response is obtained to speech at 65 dB SPL No significant response is obtained to speech at 65 dB SPL or to speech at 75 dB SPL Morphology normal for age Morphology abnormal for age Low residual noise High residual noise All is well Repeat test Re-check fitting; Consider all options Draw no conclusion !

59. Clinical implications of corticals (cont) No /t/ response Draw no conclusions from missing response ! Mixed results (and noise is low) No /g/ response No /m/ response Review HF gain or loss estimate Review mid-freq gain or loss estimate Mixed results (and noise is high) Review LF gain or loss estimate

60. Corticals for more advanced measurements

61. Application for auditory neuropathy (AN) 15% of babies found to have hearing loss at birth in NSW have AN15% of babies found to have hearing loss at birth in NSW have AN Management unclear (no device, hearing aid or cochlear implant)Management unclear (no device, hearing aid or cochlear implant) Rance showed close relationship between cortical response in older children and benefit from hearing aidsRance showed close relationship between cortical response in older children and benefit from hearing aids Gap detection worse in people with ANGap detection worse in people with AN Investigating gap detection by cortical responsesInvestigating gap detection by cortical responses

62. /Ah/ 2 second duration ms -350.0150.0650.01150.01650.02150.02650.0 µV 0.0 2.5 5.0 -2.5 -5.0 -7.5 Onset Gap Offset 0msG.avg 50msG.avg 10msG.avg 20msG.avg 5msG.avg

63. Summary Cortical responses –For checking the audibility of speech sounds –Indicate the maturity of the auditory system –Automatic detection as good as experts –Residual noise size critical –For checking hearing thresholds when the patient is awake

64. Thanks for listening www.nal.gov.au