Hearing and Deafness 1. Anatomy & physiology

1. Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab: http://www.lifesci.sussex.ac.uk/home/Chris_Darwin/ look under: "Teaching material for students" "Perception & Attention"

2. Outer, middle & inner ear Capture; Amplify mid-freqs Vertical direction coding Protection Impedance match Frequency analysis Transduction

3. Middle ear structure

4. Stapedius reflex

5. Conductive hearing loss • Sounds don’t get into cochlea • Middle ear problems • Helped by surgery and by amplification

6. Outer, middle & inner ear Capture; Amplify mid-freqs Vertical direction coding Protection Impedance match Frequency analysis Transduction

7. Cochlea

8. Cochlea cross-section

9. Travelling wave on basilar membrane sorts sounds by frequency

10. Reponse of basilar membraneto sine waves Each point on the membrane responds best to a different frequency: high freq at base, low at apex. praat amadeus

11. Organ of Corti

12. Inner hair cell

13. Hair Cell Stereocilia

14. Auditory nerve innervation IHC (1) radial afferent (blue) lateral efferent (pink) OHC (2) spiral afferent (green) medial efferent (red)

15. Auditory nerve rate-intensity functions

16. Phase Locking of Inner Hair Cells Auditory nerve connected to inner hair cell tends to fire at the same phase of the stimulating waveform.

17. Phase-locking

18. Inner vs Outer Hair Cells

19. Inner vs Outer Hair Cells

20. OHC movement Passive No OHC movement Active With OHC movement

21. OHC activity OHCs are relatively more active for quiet sounds than for loud sounds. They only amplify sounds that have the characteristic frequency of their place. • Increases sensitivity (lowers thresholds) • Increases selectivity (reduces bandwidth of auditory filter) • Gives ear a logarithmic (non-linear) amplitude response • Produce Oto-acoustic emissions

22. Conductive vs Sensori-neural deafness Mostly a combination of OHC and IHC damage Becomes linear, so No combination tones Or two-tone suppression

23. Auditory nerve frequency-threshold curves

24. Auditory tuning curves Inner hair-cell damage Healthy ear

25. Outer-hair cell damage

26. BM becomes linear without OHCs (furosemide injection)

27. Amplification greater and tuning more selective at low levels Robles, L. and Ruggero, M. A. (2001). "Mechanics of the mammalian cochlea," Physiological Review 81, 1305-1352.

28. Normal auditory non-linearities • Normal loudness growth (follows Weber’s Law) • Combination tones 880->1320 • Two-tone suppression • Oto-acoustic emissions