Issues in Human Auditory Development

1. Issues in Human Auditory Development Lynne Werner Dept. Speech and Hearing Sciences University of Washington

2. Auditory development?

4. Stages of auditory development • Encoding of sound (to 6 months of age) • Selectivity of sound processing (to 7 yr) • Flexibility in sound processing (to adulthood)

5. Sites of postnatal auditory system maturation • Peripheral • Low-level neural (brainstem) • High-level neural (cortex)

6. Immaturity is “additive” Infant Encoding Threshold Selectivity Flexibility Adult

7. Experience with sound is a major contributor to auditory development

8. Maturation of sound encoding • Sensitivity to sound • Spectral resolution • Temporal resolution

9. Sensitivity to sound: pure-tone thresholds

10. Sensitivity to sound Werner & Holmer, in preparation

11. Why does sensitivity to sound change? Conductive maturation

12. -15 -10 -5 Conductance (dB re: adults) 0 5 10 15 0.5 1 2 4 8 Frequency (kHz) 10 0.4 Conductive maturation Werner & Holmer, in preparation

13. 20 15 3 months 10 5 0 -5 -10 -15 15 6 months 10 Conductance (residual after frequency partialled out) 5 0 -5 -10 -15 15 Adults 10 5 0 -5 -10 -15 -25 -20 -15 -10 -5 0 5 10 15 20 Threshold (residual after frequency partialled out) r = -.53 Conductive maturation r = -.36 r = -.50 Werner & Holmer, in preparation

14. Why does sensitivity to sound change? • Conductive maturation • Maturation of efficiency of transmission through the brainstem

15. Maturation of neural transmission Werner, Folsom, & Mancl (1994) Hearing Research, 77: 88.

16. Why does sensitivity to sound change? • Conductive maturation • Cochlear maturation? • Maturation of efficiency of transmission through the brainstem

17. Spectral resolution Nguyen et al. (1994 ) J Acoust Soc Am96: 33

18. ? Spectral resolution Tuning curve Level Q10 = Probe frequency Level Bandwidth Frequency Masker Frequency

19. ABR Spetner & Olsho (1990) Child Dev61: 632 Folsom & Wynne (1987) J Acoust Soc Am 81:412 Spectral resolution Psychophysical

20. Temporal resolution Amplitude Time Van Tasell et al. (1987) J Acoust Soc Am 82:1152.

21. Temporal resolution? • Gap detection immature in behavioral threshold, but not in evoked potentials. • AM detection immature, but increasing modulation rate does not have a drastically different effect on infant than adult AM detection. • Forward masking looks mature at 6 months, but immature at 3 months. • Tone-onset-time and voice-onset-time sensitivity similar to adult.

22. What is the role of experience in early auditory development?

23. Role of experience “normal” auditory experience Tuning of neurons in the inferior colliculus Baby - broad Adult - sharp Threshold Frequency Sanes & Constantine-Paton (1985) J Neurosci5: 1152

24. Baby - broad Adult - broad Threshold Frequency Role of experience Tuning of neurons in the inferior colliculus clicks Sanes & Constantine-Paton (1985) J Neurosci5: 1152

25. Early audition • Reduced sensation level • Fuzzy representation of spectral characteristics of sound • Possibly good representation of changes in sound amplitude over time • Development probably depends on sound input.

26. Sure, I hear the difference. It doesn’t take much!

27. Maturation of selectivity

28. Listening selectively Level Frequency

29. Listening selectively Bargones & Werner (1994) Psychol Sci5: 170

30. Listening unselectively (kHz) Bargones & Werner (1994) Psychol Sci5: 170

31. Children use different information in phoneme identification • Nittrouer: Global, transition-carried information about syllable structure Nittrouer (2006) J Acoust Soc Am 120: 1799. • Sussman: More acoustically distinctive information in face of sensory limitations Sussman (2001) J Acoust Soc Am 109: 1173. • Mayo and Turk: Sometimes more acoustically distinctive information, but sometimes less efficient in use of more distinctive information. Mayo & Turk (2005) J Acoust Soc Am 118: 1730.

32. The spectral and temporal information in speech is represented in the infants’ and child’s auditory system. Distinctive v. similar spectral inforrmation Mayo & Turk (2005) J Acoust Soc Am 118: 1730.

33. Possible underlying mechanisms • Perceptual separation • Selective attention • Learning of less salient or more variable acoustic cues requires more experience

34. Role of experience? • Is experience with sound necessary for the development of perceptual separation or selective attention? • Experience is certainly required to build up detailed representations of speech.

35. Implications of unselective, global listening

36. Implication: Susceptibility to distraction

37. Susceptibility to distraction Leibold & Werner (2006) J Acoust Soc Am 119: 3960

38. Implication: Learning speech in noisy environments

39. Maturation of flexibility

40. Adults 11;6-12;6 6;0-7;6 Maturation of flexibility Full cues Single cues Hazan & Barrett (2000) J Phonetics28, 377.

41. Role of experience Clearly kids have to hear speech in lots of different contexts to learn which cues work best under what conditions.

42. Implication: Children can still get messed up under difficult listening conditions. If you want kids to understand something, don’t make the listening conditions difficult.

43. Conclusions • The course of auditory development is prolonged. • Early in postnatal life, the primary change in hearing has to do with the quality of the neural representation of sound. • Later in infancy and well into childhood, changes in hearing have to do with isolating fine acoustic details. • During later childhood, children are still learning when to listen to those details.

44. Thanks to • Nancy Spetner, Jill Bargones, Lori Leibold and all members of the Infant Hearing Lab past and present. • Funding from NIDCD.

45. Presentation available at http://faculty.washington.edu/lawerner/asha2006