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 stationary, achromatic patterns, but responds highly abnormally to saturated chromatic, and especially red stimuli. We now report that like chromatic stimuli, moving black and white patterns elicit an inhibitory response which extends beyond the visual field area covered by the moving 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 latter differ in several respects, and we conclude that they have different neural origins. We show that in addition to their separate inhibitory actions on detection of achromatic patterns, movement and colour exert mutually inhibitory effects. Movement is markedly effective in limiting the inhibitory spread associated with colour, regardless of the positions in the visual field of the moving and coloured stimuli. Such spatially diffuse activity is characteristic of higher visual processing in pre-occipital cortical visual areas.