National Acoustic Laboratories Cooperative Research Centre for Hearing

1. 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 National Acoustic Laboratories Cooperative Research Centre for Hearing *Speech Science, The University of Auckland, New Zealand ** Audiology, Macquarie University

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

3. So baby, how does it sound? Objective hearing aid evaluation for: • young infants • difficult-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 infants • More likely to correlate well with perception • Can be elicited by a range of speech phonemes – close to desired outcomes • Stimuli handled reasonably by hearing aids • Can 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. P2 N1 5.0 P1 2.5 µV 0.0 -2.5 0.0 100.0 200.0 300.0 400.0 500.0 600.0 Adult

12. Adult grand mean waveforms at Cz Speech Tones

13. Cortical responses in infants

14. 15.0 10.0 µV 5.0 0.0 -5.0 -100.0 0.0 100.0 200.0 300.0 400.0 500.0 600.0 ms Infants P N

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

16. NAL data Sharma et al Latency versus age

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

18. 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

19. Cortical responses in infants to different speech sounds

20. + MM OO OR UU EE AH SH SS - 400.00 600.00 0.00 200.00 ms Grand Average n = 16 infants

21. Number of subjects (out of 20) with significant differences between responses

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

23. Three stimuli m t g

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

25. Automatic detection of cortical responses

26. Hotellings T2 Desirable characteristics • No reliance on a template • Able to use information from contributing portions of waveform • Able to discount non-contributing portions of waveform

27. Analysis using Hotellings t2 statistic • Divide each record into 50 ms time bins • Average data points within each time bin • Use these averages as variables in Hotellings t2 analysis • Result is probability of the waveform being random noise X3 Voltage Time X = a1X1 + a2X2 + ........ + a9X9 Test: is there any set of weighting coefficients for which X ≠ 0?

28. Presentation of average response in series

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

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

31. d’ results - for 200 stimuli

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

33. Growth of amplitude with SLadults; tonal stimuli

34. Loudness growth above threshold Hellman & Meiselman, 1990

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

36. …….. but infants move around !

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

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

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

40. Parent’s Evaluation of Aural/oral performance in Children (PEACH) Questionnaire • 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).

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

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

43. Active electrodes

44. Capacitive Coupling 50 Hz Passive Electrodes

45. Capacitive Coupling 50 Hz Active Electrodes

46. Capacitive Coupling 50 Hz Active Electrodes Passive Electrodes

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

48. 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 children • For many years cortical response audiometry has been regarded as the “gold standard” for objective electrophysiological hearing assessment

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

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