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Carlo A. Marzi
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2010) 22 (5): 888–902.
Published: 01 May 2010
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Following destruction or deafferentation of primary visual cortex (area V1, striate cortex), clinical blindness ensues, but residual visual functions may, nevertheless, persist without perceptual consciousness (a condition termed blindsight ). The study of patients with such lesions thus offers a unique opportunity to investigate what visual capacities are mediated by the extrastriate pathways that bypass V1. Here we provide evidence for a crucial role of the collicular–extrastriate pathway in nonconscious visuomotor integration by showing that, in the absence of V1, the superior colliculus (SC) is essential to translate visual signals that cannot be consciously perceived into motor outputs. We found that a gray stimulus presented in the blind field of a patient with unilateral V1 loss, although not consciously seen, can influence his behavioral and pupillary responses to consciously perceived stimuli in the intact field (implicit bilateral summation). Notably, this effect was accompanied by selective activations in the SC and in occipito-temporal extrastriate areas. However, when instead of gray stimuli we presented purple stimuli, which predominantly draw on S-cones and are thus invisible to the SC, any evidence of implicit visuomotor integration disappeared and activations in the SC dropped significantly. The present findings show that the SC acts as an interface between sensory and motor processing in the human brain, thereby providing a contribution to visually guided behavior that may remain functionally and anatomically segregated from the geniculo-striate pathway and entirely outside conscious visual experience.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2000) 12 (5): 869–877.
Published: 01 September 2000
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To study the electrophysiological correlates of conscious vision, we recorded event-related potentials (ERPs) in a patient with partial unilateral visual extinction as a result of right-hemisphere damage. When, following bilateral presentations, contralesional stimuli were not perceived, there was an absence of the early attention-sensitive P1 (80-120 msec) and N1 (140-180 msec) components of the ERP response. In contrast, following unilateral presentations, or in those bilateral presentations in which contralesional stimuli were perceived (about 60%), these ERP components were present. These results provide novel evidence that extinction involves the stage of early focusing of attention and that the P1 and N1 components of visual ERPs are reliable physiological correlates of conscious vision.