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![Page 1: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:](https://reader035.fdocuments.in/reader035/viewer/2022070306/5516006a550346d46f8b5b09/html5/thumbnails/1.jpg)
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"
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Protection
Impedance match
Capture; Amplify mid-freqs
Vertical direction coding
Frequency analysis
Transduction
Outer, middle & inner ear
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Middle ear structure
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Stapedius reflex
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Conductive hearing loss
• Sounds don’t get into cochlea
• Middle ear problems
• Helped by surgery and by amplification
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Protection
Impedance match
Capture; Amplify mid-freqs
Vertical direction coding
Frequency analysis
Transduction
Outer, middle & inner ear
![Page 7: Hearing and Deafness 1. Anatomy & physiology Chris Darwin Web site for lectures, lecture notes and filtering lab:](https://reader035.fdocuments.in/reader035/viewer/2022070306/5516006a550346d46f8b5b09/html5/thumbnails/7.jpg)
Cochlea
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Cochlea cross-section
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Travelling wave on basilar membrane sorts sounds by frequency
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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
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Organ of Corti
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Inner hair cell
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Hair Cell Stereocilia
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Auditory nerve innervation
OHC (2)
spiral afferent (green)
medial efferent (red)
IHC (1)
radial afferent (blue) lateral efferent (pink)
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Auditory nerve rate-intensity functions
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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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Phase-locking
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Inner vs
Outer Hair Cells
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Inner vs Outer Hair Cells
Inner Hair Cells Outer Hair Cells
Sensory Motor
Afferent nerves Efferent nerves
Single row c.3 rows
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OHC movement
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PassiveNo OHC movement
ActiveWith OHC movement
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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.
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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
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Auditory nerve frequency-threshold curves
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Auditory tuning curves
Healthy ear
Inner hair-cell damage
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Outer-hair cell damage
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BM becomes linear without OHCs (furosemide injection)
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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.
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Normal auditory non-linearities
• Normal loudness growth (follows Weber’s Law)
• Combination tones 880->1320
• Two-tone suppression
• Oto-acoustic emissions