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Marco Tamietto, Franco Cauda, Luca Latini Corazzini, Silvia Savazzi, Carlo Marzi, Rainer Goebel, Lawrence Weiskrantz, Beatrice de Gelder; Collicular vision guides non-conscious behavior. Journal of Vision 2008;8(6):67. doi: 10.1167/8.6.67.
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Following destruction of the primary visual cortex (V1) phenomenal blindness ensues. There is however a multiplicity of parallel pathways, many of older evolutionary origin, that by-pass V1 and project to other targets in the brain. In a conjoint behavioral/fMRI study we provide conclusive demonstration 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 show that a stimulus in the blind field of a patient with unilateral V1 lesion, although not consciously seen, influences his responses to consciously perceived stimuli in the intact field and is accompanied by activation in the SC. However, when the stimulus is colored purple, and is hence rendered invisible to the SC, it no longer influences visuo-motor responses, and the activation in the SC drops significantly.
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