A NEW ABNORMALITY OF HUMAN VISION PROVIDES EVIDENCE OF INTERACTIONS BETWEEN CORTICAL MECHANISMS SENSITIVE TO MOVEMENT AND THOSE SENSITIVE TO COLOR

We present the results of a psychophysical study on a human observer, MW, which describe his abnormal visual responses to moving stimuli. It has been shown previously that this subject has normal vision for sta tionary, achromatic patterns, but responds highly abnormally to satura ted chromatic, and especially red stimuli. We now report that like chr omatic stimuli, moving black and white patterns elicit an inhibitory r esponse which extends beyond the visual field area covered by the movi ng stimulus itself, and suppresses detection of stationary, achromatic patterns. Although both chromatic and moving stimuli generate similar percepts in association with their inhibitory activities, these latte r differ in several respects, and rye conclude that they have differen t neural origins. We show that in addition to their separate inhibitor y actions on detection of achromatic patterns, movement and colour exe rt mutually inhibitory effects. Movement is markedly effective in limi ting the inhibitory spread associated with colour, regardless of the p ositions in the visual field of the moving and coloured stimuli. Such spatially diffuse activity is characteristic of higher visual processi ng in pre-occipital cortical visual areas.