VISUAL EXTINCTION AND CORTICAL CONNECTIVITY IN HUMAN VISION

Visual extinction is a common, poorly understood, consequence of unila teral cerebral damage, where a patient fails to detect one of two simu ltaneously presented stimuli (the one more contralateral to the lesion ), despite the fact that each stimulus is correctly detected when pres ented in isolation. The phenomenon implies a failure of shifting atten tion from an attended object to an unattended one. We show here that p air detection is improved in conditions where the two stimuli presente d to the two halves of the visual field are proximal, co-oriented and co-axial. It is further shown that stimulus properties producing reduc ed extinction correlate with the selectivity pattern of spatial latera l interactions observed in the primary visual cortex. We suggest that neuronal activity in early stages of cortical visual processing encode s, using long-range lateral interactions, an image description in whic h visual objects are already segmented and marked. Segmentation seems to function properly even in the presence of significant destruction o f the parietal cortex leading to extinction. (C) 1997 Elsevier Science B.V.