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Vision for Cognition and Vision for Survival (3).docx

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McMaster University
Gautam Ullal

November 5 , 2012 Psych 2E03: Sensory Processes Vision for Cognition and Vision for Survival (3) Vignettes with lesions in the ventral and dorsal stream - lesion-experiments in monkeys:  object discrimination: based on colour form  landmark discrimination: identify an object in relation to the position of another (dorsal stream) Optic Ataxia - disorder of visually guided movements of the arms towards a goal with damage to dorso-dorsal stream - not able to coordinate the movement along with their eyes Lesion in dorsal stream - akinetopsi - may be direction specific - inability to perceive movement - not able t perceive the level of coffee raising but can notice it spilling over as the direction of the flow of liquid changes - seeing in frames and not in a continuous manner Hemi neglect - problem in paying attention to one half of the body - lesion in the right parietal lobe - lesion in ventro-dorsal (involved in spatial location) stream especially on the right side Visual agnosia and prosopagnosia - visual agnosia: not able to recognize, lesion in V4 area ventral stream - prosopagnosia: inability to recognize faces, lesion in fusiform face area of ventral stream Apraxia - impaired performance in learnt movement - loss the ability to perform a learnt movement - problem in dorsal stream which is involved in motor memory - the ‘how’ stream SImultagnosia - inability to recognize more than one thing at a time Dorsal Simultanagnosia - inability to shift attention to one point from another - eyes or attention will fix on one particular component of the scene - inability to recognize two or more things at the same time - cannot shift from one to the next (fixed to one point) – can have reading difficulties - cannot move easily between objects without bumping – typically dorsal pathway involved Ventral Simultanagnosia - cannot bind things to together - things may be appearing from different locations and not able to bind them together - inability to recognize two or more things at the same time (just like dorsal simultanagnosics) but they can shift from one to the next, one after another. Therefore can more easily between objects (without bumping) - however, they cannot relate one object with another – typically seen in ventral pathway damage Bilateral damage to posterior parietal lobes (Balint’s syndrome) - example of dorsal simultanagnosia William’s syndrome - excessively friendly - cannot discriminate between a stranger and a friend - related to cardiac problems and problems
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