HIS 140 - Loudness and the Cochlear Amplifier

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HIS 140 - Loudness and the Cochlear Amplifier

  1. 1. Loudness & the Cochlear Amplifier When the basilar membrane and all ofthe hair cells within the organ of Cortiare healthy, the cochlea may beconsidered a sixty decibel compressoramplifier.
  2. 2. Loudness & the Cochlear AmplifierThis “amplification” resembles acompression channel in a digitalhearing instrument. For example,when increased sound pressure isreceived, the compressor reduces itsamplification performance.
  3. 3. Loudness & the Cochlear AmplifierAs the outer hair cells within the Organof Corti become damaged, the cochlearamplifier losses its ability to amplify.
  4. 4. Loudness & the Cochlear AmplifierThe compressor becomes more linearas more outer hair cells are missing.By the time a sixty decibelsensorineural loss is revealed onlyinner hair cells remain.
  5. 5. Loudness & the Cochlear Amplifier The basilar membraneThe inner and outer hair cells arearranged along the basilar membranesuch that pitch (frequencies) areperceived in a specific place within acertain area of the basilar membrane.
  6. 6. Loudness & the Cochlear Amplifier The basilar membraneThe are twenty-four filter bands alongthe basilar membrane. A pure tonesignal (the most discreet sound we canprovide) creates a wide excitationpattern upon a specific area of thesetwenty-four filter bands.
  7. 7. Loudness & the Cochlear Amplifier The basilar membraneThe high frequencies are located along theportion of the basilar membrane closest tothe oval window. Let’s reference theplacement of all commonly tested puretones along the basilar membrane. (Ref. Vonlanthen page # 103)
  8. 8. Loudness & the Cochlear Amplifier The Basilar Membrane As may be noted, if more than onepure tone frequency is present i.e.broadband sound, the more hair cellswill be stimulated resulting in anincrease of cochlear amplification.
  9. 9. Loudness & the Cochlear Amplifier The Basilar Membrane If outer hair cells become damaged ormissing, frequency resolution isremoved as well as cochlearamplification.
  10. 10. Loudness & the Cochlear Amplifier “Loud but not clear”When the number of hair cells providinghigh frequency resolution have beenreduced, an abnormal growth of loudness isperceived due to the low frequency haircells continuing to provide a sensation ofloudness through the cochlear amplifier ofbasilar membrane movement.
  11. 11. Loudness & the Cochlear Amplifier Loudness Perception The perception of loudness is verydependant upon the amount offrequency bandwidth presented to theear. Discreet amplification resolutioncan of often be of benefit for thosewith cochlear hearing loss.

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