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  • Hearing and Deafness 1. Anatomy & physiology

    Chris DarwinWeb site for lectures, lecture notes and filtering lab:http://www.lfesci.sussex.ac.uk/home/Chris_Darwin/

    look under: "Teaching material for students" "Perception & Attention"

  • ProtectionImpedance match

    Capture; Amplify mid-freqsVertical direction coding

    Frequency analysisTransduction

    Outer, middle & inner ear

  • Middle ear structure

  • Conductive hearing loss

    Sounds dont get into cochlea

    Middle ear problems

    Helped by surgery and by amplification

  • ProtectionImpedance match

    Capture; Amplify mid-freqsVertical direction coding

    Frequency analysisTransduction

    Outer, middle & inner ear

  • Cochlea

  • Cochlea cross-section

  • Travelling wave on basilarmembrane sorts sounds by frequency

    distance along basilar membrane

    amp

    litu

    de

    of

    vib

    rati

    on

    base apex

    high frequencies low frequencies

    0

  • Reponse of basilar membraneto sine waves

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

    amadeus praat

  • Organ of Corti

  • Innerhair cell

  • Hair CellStereocilia

  • Auditory nerve innervation

    OHC (2)spiral afferent (green)medial efferent (red)

    IHC (1)

    radial afferent (blue)lateral efferent (pink)

  • Auditory nerverate-intensity functions

    log amplitude (dB SPL)

    100

    80

    60

    40

    20

    sp

    ikes

    / s

    eco

    nd

    30 60 90

    high spontaneous rate

    low spontaneous rate

    saturation

    many

    few

  • Phase Locking of Inner Hair Cells

    Auditory nerve connected to inner hair cell tends to fireat the same phase of the stimulating waveform.

  • Phase-locking

    pres

    sure

    -1

    -0.5

    0

    0.5

    1

    0 0.2 0.4 0.6 0.8 1

    Inter-spike IntervalsResponse to Low Frequency tones

    time (t)

    volta

    ge

    Response to High Frequency tones > 5kHzRandom intervals

    time (t)

    2 periods 1 period nerve spike

    volta

    ge

  • Innervs

    OuterHair Cells

  • Inner vs Outer Hair CellsInner Hair Cells Outer Hair Cells

    Sensory Motor

    Afferent nerves Efferent nerves

    Single row c.3 rows

  • OHC movement

    PassiveNo OHC movement

    ActiveWith OHC movement

  • 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 forloud sounds.They only amplify sounds that have the characteristicfrequency of their place.

  • 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, soNo combination tonesOr two-tone suppression

    Mostly a combination ofOHC and IHC damage

  • Auditory nerve frequency-threshold curves

    log frequency

    log

    am

    pli

    tud

    e (d

    B S

    PL

    )

    100

    80

    60

    40

    20

    Characteristic Frequency

    Normal Threshold

    Normal bandwidth

  • Auditory tuning curves

    log frequency

    log

    am

    pli

    tud

    e (d

    B S

    PL

    ) 100

    80

    60

    40

    20Characteristic Frequency

    Normal Threshold

    Abnormal Threshold

    Normal bandwidth

    Normal bandwidth

    Healthy ear

    Inner hair-celldamage

  • Outer-hair cell damage

    log frequency

    log

    am

    pli

    tud

    e (d

    B S

    PL

    ) 100

    80

    60

    40

    20

    Characteristic Frequency

    Normal Threshold

    Abnormal Threshold

    Normal bandwidth

    Abnormal bandwidth

  • BM becomes linear without OHCs(furosemide injection)

  • Amplification greater and tuningmore selective at low levels

    Robles, L. and Ruggero, M. A. (2001). "Mechanics of the mammalian cochlea," Physiological Review 81, 1305-1352.

  • Normal auditory non-linearities

    Normal loudness growth (follows Webers Law)

    Combination tones

    Two-tone suppression

    Oto-acoustic emissions