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Central Auditory System 5. Function.docx

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McMaster University
Paul Faure

November 5 , 2013 Psych 3A03: Audition Central Auditory System 5. Function Graphical Displays of Phase Following - Behaviourist and physiologists use graphics to display degree of phase locking of neural activity or acoustic behaviour - Examples of common graphical phase locking displays include: 1. Phase or period histogram (examples is a phase histogram) 2. Interspike interval histogram What is a Histogram? - Stimulus is repeated n times - The responses from n presentations are counted and summed into discrete time bins - Response plotted as bar graph or histogram Period Histogram - Neural responses plotted with the wave form of a complex stimulus - Spikes counted at same starting phase of stimulus - Histogram builds up spike counts over repeated stimulus presentations and shows count over one period (but not in textbook example) - Discharges usually occur only to one phase of waveform (i.e. responses are rectified) - Coefficient of synchronization quantifies phase locking as synchrony of spike discharges  How tightly clustered are the responses to any given phase?  Clustering at a particular phase angle would suggest that there is phase locking - CS = 0, no phase locking - CS = 1, perfect phase locking Coefficient of Synchronization - Timing of spikes is usually synchronized to specific period of stimulus waveform - Coefficient of synchronization quantifies phase locking as synchrony of spike discharge  CS = 0, no phase locking  CS = 1, perfect locking  Measured in vectors  Long vector means tight phase locking  Short vector means little phase locking  Vector strength vs. modulation rate - Vector strength: magnitude of coefficient of synchronisation to quantity degree of phase locking Interspike Interval Histogram - Interspike interval histograms provide means of examining the regularity of spike timing - X-axis: time between successive action potentials - Y-axis: the relative Click Interspike Interval (ISI) Histogram - Output does not match the input for a click passed through a bandpass filter - Response of ANFs to an acoustic transient or click (white noise) stimulus reveals information on transduction process - Periodic peaks in ISI histogram indicate that biomechanical processing of click is similar to passing the click through an electrical bandpass filter Impulse Response of a Filter - Time domain appearance of waveform is altered when signal is passed through electrical filter - Characterised by measuring the filter’s impulse response - Impulse response defines filter’s time to settle to a steady state - Impulse response also indicates stability. An impulse response that continues to oscillate (ring) in time domain indicates that the filter may be prone to instability - Impulse response defines the filter temporal and spectral response - The time period between peaks in the temporal oscillations is proportional to the reciprocal of the filter’s center frequency - Center frequency = 1/T (T times between the spikes) Click Measures Impulse Response of ANF - Periodic oscillations of AND is ringing of
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