class+13+lecture-1 - Sensation and Perception Class XIII:...

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Sensation and Perception Class XIII: Hearing Physiology (cont.) & Auditory Scene Perception
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Basic Structure of the Mammalian Auditory System Organ of Corti : A structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers Movements of cochlear partition are translated into neural signals by structures in the organ of Corti
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Figure 9.11 The cochlea (cont’d)
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Basic Structure of the Mammalian Auditory System Tectorial membrane : A gelatinous structure, attached on one end, that extends into the middle canal of the ear, floating above inner hair cells and touching outer hair cells Vibrations cause displacement of the tectorial membrane, which bends stereocilia attached to hair cells and causes the release of neurotransmitters
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Figure 9.12 Vibration causes a displacement along the cochlear partition, resulting in deflection of stereocilia
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Basic Structure of the Mammalian Auditory System Stereocilia : Hairlike extensions on the tips of hair cells in the cochlea that initiate the release of neurotransmitters when they are flexed The tip of each stereocilium is connected to the side of its neighbor by a tiny filament called a tip link
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Figure 9.13 Stereocilia regulate the flow of ions into and out of hair cells (Part 2)
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Figure 9.13 Stereocilia regulate the flow of ions into and out of hair cells (Part 1)
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Basic Structure of the Mammalian Auditory System Coding of amplitude and frequency in the cochlea Place code : Tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition with the greatest mechanical displacement
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Figure 9.14 The cochlea is tuned to different frequencies Spatial code for frequency
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Basic Structure of the Mammalian Auditory System Inner and outer hair cells: Inner hair cells : Convey almost all information about sound waves to the brain (using afferent fibers) Outer hair cells : Convey information from the brain (using efferent fibers). They are involved in an elaborate feedback system
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Basic Structure of the Mammalian Auditory System The auditory nerve (AN) Responses of individual AN fibers to different frequencies are related to their place along the cochlear partition Frequency selectivity : The property of AN fibers that describes how they are most responsive to certain frequencies. Clearest when sounds are very faint Threshold tuning curve : A map plotting thresholds of a neuron or fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response
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Figure 9.15 Threshold tuning curves for six auditory nerve fibers
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Basic Structure of the Mammalian Auditory System Rate saturation Are AN fibers as selective for their characteristic frequencies at levels well above threshold as they are for barely audible sounds? To answer this, look at
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class+13+lecture-1 - Sensation and Perception Class XIII:...

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