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Petya D. Radoeva, David H. Brainard, Geoffrey K. Aguirre; Contrast responses and retinotopic organization in Blindsight: an fMRI study. Journal of Vision 2006;6(6):541. doi: 10.1167/6.6.541.
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It has been debated whether residual vision in blindsight/Riddoch's phenomenon is mediated by subcortical projections to extrastriate areas or whether there are contributions from spared V1 cortex. Here we tested patient MC who sustained a left PCA stroke at the age of 16. Her initial right homonymous hemianopia later recovered to a scotoma with macular sparing. Behavioral studies have demonstrated a statokinetic dissociation within her scotomatous field. In the current 3T fMRI study, we examined neural contrast response functions and retinotopic organization in her normal and affected hemispheres. Expanding/contracting concentric rings of eight different levels of contrast (ranging from 1% to 100%) were presented within the scotoma, or in the healthy visual field. In the healthy hemisphere, activation was observed in areas V1, V2/V3, hV4, and MT, and the contrast response functions were comparable to those of Liu and Wandell, 2005. In the affected hemisphere, there was robust activation in areas V2v/V3v, hV4, and MT, and more subtle activation within area V1. All of these areas retained contrast sensitivity at high levels of contrast, but had reduced sensitivity for low contrast levels. Retinotopic mapping revealed spatially organized signals within V1, adjacent to her lesion. Eccentricity representation within V1 included her scotomatous field in which the stimuli from the contrast experiment were presented. The current study demonstrates that it is possible to observe retinotopic organization, and contrast sensitivity, in spared V1 cortex for stimuli presented in the scotoma of a patient who clinically presents with Riddoch's phenomenon.
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