FUNCTIONAL-ANALYSIS OF PRIMARY VISUAL-CORTEX (V1) IN HUMANS

Human area V1 offers an excellent opportunity to study, using function al MRI, a range of properties in a specific cortical visual area, whos e borders are defined objectively and convergently by retinotopic crit eria. The retinotopy in V1 (also known as primary visual cortex, stria te cortex, or Brodmann's area 17) was defined in each subject by using both stationary and phase-encoded polar coordinate stimuli. Data from V1 and neighboring retinotopic areas were displayed on flattened cort ical maps. In additional tests we revealed the paired cortical represe ntations of the monocular ''blind spot.'' We also activated area V1 pr eferentially (relative to other extrastriate areas) by presenting radi al gratings alternating between 6% and 100% contrast. Finally, we show ed evidence for orientation selectivity in V1 by measuring transient f unctional MRI increases produced at the change in response to gratings of differing orientations. By systematically varying the orientations presented, we were able to measure the bandwidth of the orientation ' 'transients'' (45 degrees).