THE REPRESENTATION OF THE IPSILATERAL VISUAL-FIELD IN HUMAN CEREBRAL-CORTEX

Previous studies of cortical retinotopy focused on influences from the contralateral visual field, because ascending inputs to cortex are kn own to be crossed, Here, functional magnetic resonance imaging was use d to demonstrate and analyze an ipsilateral representation in human vi sual cortex, Moving stimuli, in a range of ipsilateral visual field lo cations, revealed activity: (i) along the vertical meridian in retinot opic (presumably lower-tier) areas; and (ii) in two large branches ant erior to that, in presumptive higher-tier areas, One branch shares the anterior vertical meridian representation in human V3A, extending sup eriorly toward parietal cortex, The second branch runs antero-posterio rly along lateral visual cortex, overlying motion-selective area MT, I psilateral stimuli sparing the region around the vertical meridian rep resentation also produced signal reductions (perhaps reflecting neural inhibition) in areas showing contralaterally driven retinotopy, Syste matic sampling across a range of ipsilateral visual field extents reve aled significant increases in ipsilateral activation in V3A and V4v, c ompared with immediately posterior areas V3 and VP, Finally, compariso ns between ipsilateral stimuli of different types but equal retinotopi c extent showed clear stimulus specificity, consistent with earlier su ggestions of a functional segregation of motion vs, form processing in parietal vs, temporal cortex, respectively.