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Anoxic Visual System

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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, and 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—which is an “inability or marked difficulty in visually identifying an object or picture of an object as a result of impaired perceptual…show more content…
However, unlike the healthy control participants, “D.F. did not show activation in the superior parieto-occipital sulcus, […which] has been shown to be activated during arm movement tasks” (James et al., 2006). MRI images revealed anatomical abnormalities outside of the ventral stream. Despite this finding, researchers James et al. (2006) concluded from the experiments that the affected structures remained functional. According to Pisella et al. (2006) “this may be partially explained by the reorganization of surrounding intact brain tissue” (Pisella, Binkofski, Lasek, Toni, & Rossetti, 2006). After sustaining damage, the brain could have shown plasticity; new neuronal connections from areas outside the damage site took over some of the function that was impaired from the lesion. Therefore, this would indicate why D.F., was able to perform the arm movement task, despite the marked…show more content…
By comparing the deficits that arise from lesioning the occipitoparietal stream (optic ataxia) to those caused from lesioning the occipitotemporal stream [visual agnosia (VA)], inferences pertaining to a double dissociation in this anatomical dichotomy can be made. Arguments against a double dissociation in the visual streams come from research by Pisella et al., (2006), which looks at 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). Thus, no conclusions with regards to a double dissociation can be made. 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
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