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Localization of Sound (2).docx

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Gautam Ullal

November 30 , 2012 Psych 2E03: Sensory Processes Localization of Sound (2) Auditory pathways – major relays - cochlear nucleus - olivary nucleus (superior olivary nucleus) - colliculus-inferior - medial geniculate - auditory cortex-area41/primary/A1 - each of the above relay centres has been investigated thoroughly for spectral sensitivity and direction sensitivity Probable role of each of the major sensory relays - cochlear nucleus:  spectral analysis - superior olivary nucleus: spatial analysis:  medial – determines interaural time difference – helpful for sound localization of low frequency sounds  lateral – determines interaural level difference – helpful for localization of high frequency sounds - inferior colliculus:  integration of spectral and spatial analysis - medial geniculate:  attending to particular spatial and spectral cues and top-down auditory signal processing Major centrifugal feedback connections in the auditory pathways - corticofugal outputs to medial geniculate (considering cortex as centre): attention to auditory cues - olivofugal outputs to outer hair cells (considering superior olivary nucleus as centre): tuning of inner hair cells - cochleofugal outputs to stapedius and tensor tympani (considering cochlear nucleus to be the centre): attenuation reflex Plasticity following monaural deprivation during critical period (rat model) amblyaudia (similar to amblyopia) - auditory acuity depends on binaural and monaural cues - monaural deprivation especially during critical periods results in significant distortion in tonotopic maps in A1 (particularly to high frequency sounds)  CF = characteristic frequency  MD = monaural deprived  Sham = control  D, V; dorsal, ventral  C, R; caudal rostral  Empty polygons = no response Auditory & visual pathways compared - relays: many more in auditory pathways - cross-over between left-right in auditory pathways - considerable left-right interaction along the auditory pathway important for localizaiton - there is cochleotopic representation on the auditory cortex for audition just as retinotopic on visual cortex for vision - there are what and where streams for audition extending from temporal cortex to parietal-frontal cortex similar to visual cortex in vision Most animals (including humans): - good at detecting the source of sound on the azimuth and poor in the vertical plane - interaural level difference (ILD) is best for high frequency sounds (binaural) - interaural time difference (ITD) is best for low frequency sounds (binaural) - monaural spectral cues for sounds in the vertical plane The cone of confusion
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