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Human Speech Production.docx

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Paul Faure

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November 6 , 2013 Psych 3A03: Audition Human Speech Production Monaural Two Tone Suppression - Presentation of 2 tones is also informative on auditory function  Tone 1 presented @ CF of ANF  Tone 2 presented off CF of ANF - Varying the frequency and SPL of tone 2 relative to tone 1 reveals regions of suppression in neural response - Amount of suppression caused by varying frequency and SPL of tone 2 is visualized by plotting on neural tuning curve of tone 1 - Cause of tone suppression is nonlinear motion of basilar membrane vibrations to 2 tones - One must be cautious in trying to predict responses of a neuron to a complex sound based on its responses to simple sounds - Can also measure two tone suppression effects on other spike parameters - E.g. spike synchrony (coefficient of synchronization), spike rate, etc. Binaural Two Tone Suppression - Ipsilateral stimulus and contralateral broadband noise suppressor - Shows similar suppressive effects - Fewer spikes and larger sound pressure levels in order for the ipsilateral tone to produce effects - Function of efferent auditory system is still not fully understood - Crossed olivocochlear bundle (COCB) fibers, from medial superior olive, are inhibitory - Binaural stimulation (both ears stimulated) if an auditory neuron often results in a suppressed neural response relative to monaural (one ear) stimulation - In vitro experiments has shown the stimulation of COCB fibers inhibits some of the ipsilateral excitatory response Encoding Frequency - Place theory of hearing says that the frequency of sound input is encoded by noting which region or place within the cochlear or auditory nerve was stimulated  Spatial representation - Temporal or volley theory of hearing says that the periodicity of neural discharges can be used to reconstruct frequency of sound input (up to limit ca. 5kHz) Encoding Amplitude - Amplitude or intensity of stimulus is encoded by number of spikes and/or discharge rate of ANFs - Dynamic range of single AND is limited to 30-50dB (point of saturation), this cannot account for the behavioural dynamic range - Combining population of many ANFs increases dynamic range of system Encoding Time (Phase) - Phase locked responses of ANFs encodes timing information, but only for periodicities up to 0.2ms (5kHz) - Timing and phase is used for location Complex Encoding of Acoustic Information - Combining information obtained from different measures into population response increases range of information encoded - ALSR = average localized synchronized (spike) rate - By looking across frequencies we are looking to see where we are getting synchronization of fibres Computational Models of Auditory Periphery - How auditory neurons might respond to a stimulus Central Auditory Nervous System (CANS) - We now understand the basics of how frequency, amplitude and timing information are encoded by peripheral auditory system (PANS) now going to have brief tour of the central auditory nervous systems (CANS) - Binaural (input from two ears) neural interactions are located in the CANS - Emergent cellular properties and neural networks take place in the CANS Flow of Central Auditory Information st - Cochlear Nucleus (1 synapse) - Trapezoid body - Superior olivary complex - Lateral lemniscus - Inferior colliculus - Medial geniculate body - Auditory cortex - Nuclei defined where cell bodies are and where the direct projects are - Ascending CANS is from cochlea toward auditory cortex - Descending CANs is from auditory cortex toward cochlea - Nuclei closer to cortex are “higher” auditory centers - Ascending afferent auditory system: auditory information that ascends CANS via afferent fiber tracts - Descending eff
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