the ear - pathway of hearingthe middle ear cont‘d auditory ossicles: mallet, anvil, stirrup: –...
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The Ear - Pathway of Hearing
Auditory PhoneticsHow to Handle Speech
UBielefeld
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What is Sound?
“ ... a sound is any disturbance of air that could cause a displacement of the eardrum which, after transmission by the bone chain, could affect the liquid in the inner ear in such a way that the auditory nerves are stimulated.”
(Ladefoged, Elements of Acoustic Phonetics, pp.2-3)
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How Sound Travels“The source of sound causes movements
of the air particles in its immediate neighborhood; these movements cause disturbances in the air a little farther away from the source; these air particles in their turn affect their neighbors which are still farther away from the source; and so the disturbance spreads outward.”
(Ladefoged, ibid, p.3)
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Just Another Sound: The Human Voice
• voice: fluctuations of air pressure > caused by rapid opening and closing of vocal folds
• pressure rises to a maximum, then falls steadily to a minimum before rising again to repeat the cycle, all within a small fraction of a second
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Varying Air Pressure
• maxima: peaks above 0• minima: valleys below 0• peaks of air pressure
<=> air particles close together
• moments of low pressure <=> air particles furthest apart
THINK: What about sound in a vacuum?
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Hearing vs. Perception
• ear (peripheral auditory organ): hearing > sound reception & sound transformation
• auditory organ (includes central nervous system; central auditory organ): perception > interpretation of semantic contents
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Our Auditory Field
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Our Auditory Field
http://home.schule.at/teaching/Hoeren_und_Hoerprobleme/vorgang/hoerfeld.htm
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The Ear
• outer ear – protection, – collection of sound
• middle ear – transmission of mechanic vibrations
• inner ear – transformation of vibrations into neural
impulses
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The Ear
outer earmiddle ear
inner ear
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The Ear Cont‘d.
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The Path of Sound
• external canal• vibrates eardrum• vibration moves through ossicles
– mallet (malleus), anvil (incus), stirrup (stapes)
• stapes vibrates oval window of cochlea• creates pressure wave in the fluid inside
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The Outer Ear • Pinna / auricle:
– protects the entrance to the ear canal
– contributes to our ability to locate sounds, esp. at higher frequencies
• Meatus/outer ear canal:– pathway for the acoustic signal– protection of the inner ear– tube resonator, i.e. favors
transmission of high-frequency sounds (2000-4000 Hz) and generally between 500 and 4000 Hz
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The Middle Ear
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The Middle Ear Cont‘d
• Eardrum:– is deflected by air pressure variations (= sound)– converts air pressure variations into mechanical movement– transmits this movement to the auditory ossicles
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The Middle Ear Cont‘d
auditory ossicles: mallet, anvil, stirrup:– pick up the mechanical movement of the eardrum and
convey it to the inner ear/oval window – transformation of air pressure variation into equivalent
mechanical movements– contraction between anvil and stirrup can reduce amplitude
(protection for inner ear)
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The Middle Ear Cont‘d
• Eustachian tube:– narrow tube connecting
pharynx and middle ear – equalizes air pressure
differences between outer and middle ear
• oval window:– interface between middle
and inner ear – transmits mechanical
movement
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The Inner Ear
• cochlea:– coil-like structure terminating in a window with a
flexible membrane at each end– internally divided by two membranes, filled with
cochlear fluid– converts mechanical movements into neural
signals
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The Inner Ear Cont‘d -Cochlea
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The Inner Ear Cont‘d
• basilar membrane:– stiffer at one end than at the other
> sensitive to particular frequencies at particular points because of the different resonance which is due to different stiffness
• high frequencies picked up at the stiff end• lower frequencies at the more flexible end> conducts spectral analysis of incoming sound
(see animation later!)
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The Inner Ear Cont‘d
cross section of onesingle turn of the cochlea
(no 5. = basilar membrane)
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The Inner Ear Cont‘d
• Organ of Corti:– attached along the basilar membrane – hair cells which get moved and excited – responsible to transform membrane displacement into neural
signals
1. inner hair cells2. outer hair cells3. tunnel of Corti4. basilar membrane
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The Inner Ear Cont‘d -Hair Cells
• about 16,000 in each cochlea
• located on the basilar membrane• do not regenerate• inner (~ 3,500) hair cells
vs. outer hair cells (~ 20,000)• stimulated by bending of the basilar membrane (length a wave travels on the basilar membrane depends on frequency > first frequency (spectral) analysis)• amplitude: lower & medium amplitudes affect outer hair cells, higher amplitudes affect inner hair cells
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Anatomy of the CochleaAnimated
http://www.hhmi.org/biointeractive/animations/cochlea/coc_frames.htm
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The Auditory Nerve
• Auditory nerve:– picks up the neural signals from the organ of Corti– sends signals to the brain where the information is
processed and interpreted > analytical effects of the human auditory system
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The End