hearing and deafness 1. anatomy & physiology chris darwin web site for lectures, lecture notes...

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

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Page 1: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

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

Page 2: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Protection

Impedance match

Capture; Amplify mid-freqs

Vertical direction coding

Frequency analysis

Transduction

Outer, middle & inner ear

Page 3: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Middle ear structure

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Page 4: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Conductive hearing loss

• Sounds don’t get into cochlea

• Middle ear problems

• Helped by surgery and by amplification

Page 5: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Cochlea

Page 6: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Cochlea cross-section

Page 7: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Travelling wave on basilar membrane sorts sounds by frequency

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Page 8: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Reponse of basilar membraneto sine waves

Each point on the membrane responds best to a different frequency: high freq at base, low at apex.

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amadeus praat

Page 9: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Organ of Corti

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Page 10: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Inner hair cell

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Page 11: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Hair Cell Stereocilia

Page 12: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Auditory nerve innervation

OHC (2)

spiral afferent (green)

medial efferent (red)

IHC (1)

radial afferent (blue) lateral efferent (pink)

Page 13: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Auditory nerve rate-intensity functions

Page 14: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Phase Locking of Inner Hair Cells

Auditory nerve connected to inner hair cell tends to fire

at the same phase of the stimulating waveform.

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Page 15: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Phase-locking

Page 16: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Inner vs

Outer Hair Cells

Page 17: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Inner vs Outer Hair Cells

Inner Hair Cells Outer Hair Cells

Sensory Motor

Afferent nerves Efferent nerves

Single row c.3 rows

Page 18: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

OHC movement

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PassiveNo OHC movement

ActiveWith OHC movement

Page 19: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

OHC activity

• Increases sensitivity (lowers thresholds)

• Increases selectivity (reduces bandwidth of auditory filter)

• Gives ear a logarithmic (non-linear) amplitude response

• Produce Oto-acoustic emissions

OHCs are relatively more active for quiet sounds than for loud sounds.

They only amplify sounds that have the characteristic frequency of their place.

Page 20: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Auditory tuning curves

Healthy ear

Inner hair-cell damage

Page 21: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Outer-hair cell damage

Page 22: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Conductive vs Sensori-neural deafness

Conductive Sensori-neural Sensori-neural

Origin Middle-ear Cochlea (IHCs) Cochlea (OHCs)

Thresholds Raised Raised Raised

Filter bandwidths Normal Normal Increased

Loudness growth Normal Normal Increased (Recruitment

Becomes linear, so

No combination tones

Or two-tone suppression

Mostly a combination of OHC and IHC damage

Page 23: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Normal vs Impaired Dynamic Range

Page 24: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:

Normal auditory non-linearities

• Normal loudness growth (follows Weber’s Law)

• Combination tones

• Two-tone suppression

• Oto-acoustic emissions