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Lecture

The Neural Code.docx

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Department
Psychology
Course Code
PSYCH 3A03
Professor
Paul Faure

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October 18 , 2013 Psych 3A03: Audition The Neural Code Phase Relation: Stapes and Traveling Wave - Basilar membrane peaks at different frequencies Basilar Membrane is a Bandpass Filter - SPL that is most sensitive to = characteristic frequency Basilar Membrane Motion Summary - Basal end of basilar membrane vibrates best to high frequencies but also responds to low frequencies - Apical end of basilar membrane vibrates only to low frequencies - There is a time lag between stapes motion and movement of apical end of basilar membrane - Greater SPLs cause larger displacement Basilar Membrane: Bank of Bandpass Filters - A given frequency causes a particular region to vibrate maximally: the characteristic frequency (CF) - Adjacent regions, particularly toward the base, also vibrate b.m. but less so than the freq that causes maximum displacement - Higher freqs have little vibration - Lower freqs have more vibration - Plot of SPL versus freq to reach same amplitude of displacement reveal bandpass filter function - 8.35kHz tone is point of maximum displacement.: this point of b.m. is tuned to 8.35kHz - Region were the amplitude is high at 8.35kHz (lower sound level) - Steep roll-off at high frequencies - Gradual roll-off at low frequencies Motion of Basilar Membrane is Nonlinear - Input-output function showing b.m. velocity vs. SPL for 9 & 1 kHz tones. The CF for this region of the b.m. is 9kHz - Motion of basilar membrane is not entirely linear with respect to SPL - Input-output function of membrane velocity shows a compressive nonlinearity at CF: at frequencies off CF, vibration is fairly linear - At characteristic frequency it is non linear - Change is compressive because steepness of curve is shallower - Relationship is more linear at SPL extremes with the CF - Relationship is more linear at frequencies above and below CF - Dynamic range changes in terms of the velocity: becomes compressed at characteristic frequencies - Results in the production of audible distortion products (e.g. harmonics and difference tones) Inner (IHC) and Outer Haircells (OHC) 1. Nucleus 2. Stereocilia 3. Cuticular plate: formed from deiter cells 4. Radial afferent ending (dendrite of type I neuron): take information form the receptor towards the brain  Radial and spinal afferent are both spiral ganglia neurons 5. Lateral efferent ending: come from the brain and go to the cochlea (motor neurons that cause motion) – does not synapse directly in the inner haircells; synapses with the afferent nerve 6. Medial efferent ending 7. Spiral afferent ending (dendrite of type II neuron) - Cell body is based in fluid that is isolated from the cell body of the inner hair cells Stereocilia of Haircells (HC) - Typically three rows that are connected - Connections between the tips of the stereocilia and the body of the previous row - Bridges between rows and within a row -
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