Psych 8 - The Sensorimotor System (191- 203, 213-218, plus...

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The Sensorimotor System (191- 203, 213-218, plus 6.6) Cortical Mechanisms of Vision and Conscious Awareness (6.6) - The primary visual cortex is that area of cortex that receives most of its input from the visual relay nuclei of the thalamus (from the lateral geniculate nuclei). Areas of secondary visual cortex are those that receive most of their input from the primary visual cortex, and areas of visual association cortex are those that receive input from the secondary areas of other sensory systems. The primary visual cortex is located in the posterior region of the occipital lobes. Most areas of secondary visual cortex are located in the prestriate cortex (the band of tissue in the occipital lobe that surrounds the primary visual cortex) and the inferotemporal cortex (the cortex of the inferior temporal lobe, posterior parietal cortex). The major flow of visual information in the cortex is from the primary visual cortex to the various areas of secondary visual cortex to the areas of association cortex. As one moves up this visual hierarchy, the neurons have larger receptive fields and the stimuli to which the neurons respond are more specific and more complex. Damage to an area of the primary visual cortex produces a scotoma, an area of blindness, in the corresponding area of the contralateral visual field of both eyes. - Blindsight is the ability of such patients to respond to visual stimuli in their scotomas even though they have no conscious awareness of the stimuli. Of all visual abilities, perception of motion is most likely to survive damage to primary visual cortex. Many pathways that conduct information from the primary visual cortex through various specialized areas of secondary and association cortex are parts of two major streams, the dorsal steam and the ventral stream. The dorsal stream flows from the primary visual cortex to the dorsal prestriate cortex to the posterior parietal cortex, and the ventral stram flows from the primary visual cortex to the ventral prestriate cortex to the inferotemporal cortex. Most visual cortex neurons in the dorsal stream respond to spatial stimuli, while those in the ventral stream respond to the characteristics of objects. - A major implication of the “where” versus “what” theory of vision is that damage to some areas of cortex may abolish certain aspects of vision while leaving others unaffected. The “control of behavior” versus “conscious perception” theory states that the dorsal stream is to direct behavioral interactions with objects, whereas the function of the ventral stream is to mediate the conscious perception of objects. Some patients with bilateral lesions to the ventral stream have no conscious experience of seeing and yet are able to interact with objects under visual guidance. Some patients with bilateral lesions to the dorsal stram can consciously see objects but cannot interact with them under visual guidance. - Prosopagnosia is a visual agnosia for faces. Agnosia is a failure of recognition that is not attributable to a sensory
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This note was uploaded on 02/09/2012 for the course PSYCH 2220 taught by Professor Culham during the Spring '11 term at UWO.

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Psych 8 - The Sensorimotor System (191- 203, 213-218, plus...

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