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Brain Mechanisms of Visual Perception.doc

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PSYC 2240
Rebecca Jubis

Brain Mechanisms of Visual Perceptionperception takes place in brainoptic nerve sends signals to thalamus which relays information to primary visual cortex located in occipital lobe neurons in primary visual cortex send visual information to two successive levels of visual association cortex first levellocated in occipital lobe surrounds primary visual cortexsecond leveldivided into 2 parts one is middle of parietal lobe and one in lower part of temporal lobeoften described as hierarchy of information processingcircuits of neurons analyze particular aspects of visual information and send results of analysis to another circuit which performs further analysisat each step successively more complex features are analyzed and higher levels interact with memories Primary Visual Cortexknowledge of early stages of visual analysis comes from investigations of activity of individual neurons in thalamus and primary visual cortex David Hubel and Torsten Wieselinserted microelectrodes into regions of visual system in anasthetized cats and monkeys unconsious but visual system still active to detect Aps produced by individual neuronsfound place in visual field with most response and objects with most responsefound that surface of retina is mapped on surface of primary visual cortexcentre of visual field is largest area2500 blocks of tissue 5x7 mm in size containing 15000 neurons each receiving information from same small region of retina and thus small region of visual field amount seen through soda strawneural circuits within module analyzes various characteristics of their own particular field receptive fielddetected presence of lines and signalled orientation of lines thickness of lines movement and its directionreceptive fieldthat portion of visual field in which presentation of visual stimuli will produce an alteration in firing rate of particular neuronparticular neuron responds to particular orientation 50 degrees etcVisual Association Cortexfirst level of visual association cortex contains several subdividions each of which contain map of visual sceneeach subdivision receives information from different types of neural circuits within modules of primary visual cortex orientation and widths of lines and edgesinvolved in perception omovementkeeps track of relative movement of objects colour 2 regions of association cortex put together information ghathered and processed by subdivisions of first level shape movement and colourcombined in visual association cortex in lower part of temporal lobe 3d form perceptionform perception information from motor system and body senses about movement of eyes
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