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Hearing and Deafness 1. Anatomy & physiology

Hearing and Deafness 1. Anatomy & physiology. Chris Darwin. Web site for lectures, lecture notes and filtering lab: http://www.lifesci.susx.ac.uk/home/Chris_Darwin/. safari. Outer, middle & inner ear. Capture; Amplify mid-freqs Vertical direction coding. Protection

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Hearing and Deafness 1. Anatomy & physiology

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  1. Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab: http://www.lifesci.susx.ac.uk/home/Chris_Darwin/ safari

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

  3. Middle ear structure

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

  5. Cochlea

  6. Cochlea cross-section

  7. Travelling wave on basilar membrane sorts sounds by frequency

  8. 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

  9. Organ of Corti

  10. Inner hair cell

  11. Hair Cell Stereocilia

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

  13. Auditory nerve rate-intensity functions

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

  15. Phase-locking

  16. Inner vs Outer Hair Cells

  17. Inner vs Outer Hair Cells

  18. OHC movement Passive No OHC movement Active With OHC movement

  19. 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

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

  21. Outer-hair cell damage

  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. Normal vs Impaired Dynamic Range

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

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