Occipitoparietal Visual System Case Study

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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, …show more content…
By comparing the deficits that arise from lesioning the occipitoparietal lobe (optic ataxia) to those caused from lesioning the occipitotemporal lobe [visual agnosia (VA)], inferences can be made pertaining to a double dissociation in this anatomical dichotomy. Arguments against a double dissociation in the visual streams come from research conducted by Pisella et al., (2006) optic ataxia and visual agnosia according to their respective visual streams. In their research, Pisella et al. (2006) revealed “patients with VA are impaired for visual object recognition in central vision while patients with OA are not” (Pisella et al., 2006). This is suggestive of a simple dissociation in the dorsal stream. However, research has not yet looked into peripheral vision for visual agnosia. Findings for peripheral vision conditions only exist for optic ataxia (Pisella et al., 2006); moreover, no conclusions can be made with regards to a double dissociation. If peripheral vision conditions for agnosia reveal that there is no dissociation between optic ataxia and visual agnosia, this could invalidate arguments in favor of a double dissociation. Thus, future research should investigate the dissociations between central and

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