Visual System Case Studies

The purpose of this study was to support the dominant view that the visual system is functionally and anatomically dichotomized according to dissociations between the ventral- and dorsal-streams. To illustrate this hypothesis, James, Culham, Humphrey, Milner, & Goodale (2003) examined the case study of patient D.F., who “suffered severe bilateral damage to her occipitotemporal visual system […], while retaining the use of her occipitoparietal visual system” (James, Culham, Humphrey, Milner, & Goodale, 2003) following an anoxic episode. Lesions to the occipitotemporal system resulted in apperceptive visual agnosia, an “inability or marked difficulty in visually identifying an object or picture of an object as a result of impaired perceptual …show more content…
are compelling, however they are only suggestive of a single dissociation between the occipitotemporal and occipitoparietal visual systems. Moreover, to add weight to the findings from D.F.’s case study, similar research by Ungerleider & Haxby (1994) investigates the double dissociation of visual recognition and visuospatial performance in patients with lesions of occipitotemporal and occipitoparietal cortex, respectively (Ungerleider & Haxby, 1994). Empirical inquiries pertaining to a double dissociation compare the outcomes of patients with lesions to the occipitotemporal stream, as seen in patients like D.F. with visual agnosia; and patients with lesions to the occipitoparietal stream, such as patients with optic ataxia. For instance, optic ataxia results in impaired action—characterized by inappropriate reaching and grasping—while maintaining intact perception; meanwhile visual agnosia results in impaired perception, while maintaining intact action. As aforementioned the two visual stream deficits are characterized by reciprocity of impairment; functioning in one deficit that the other is impaired in—and vice versa. Therefore, “the reciprocal patterns of impairment found in optic ataxia and in visual agnosia have been considered as a functional double-dissociation” (Rossetti, Pisella, & Vighetto,

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