Integration in visual movement perception

• Main Author: Costello, M.
• Published: University of Aberdeen 1981
• Subjects: 150.724
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.592274

It is argued from initial assumptions concerning space-time relationships in visual movement perception that observable continuity of movement-path, herein called trajectory, should be a key factor in determining notivation of channels subserving movement detection. Two stimulus arrangements were designed to vary this factor. In the first arrangement a moving grating was intermittently exposed; the method of temporal interruption. In the second arrangement a moving grating was masked by a superimposed stationary grating; the method of spatial interruption. Parameters of spatial and temporal interruption were varied and their perceptual effects noted, together with their effects on the motion after-effect (MAE) the main dependent measure in these studies. At moderate temporal interruption rates MAE was depressed compared with the MAE from uninterrupted movement; but it increased again at a fast interruption rate. Perceived velocity increased at moderate interruption rates. With spatially interrupted movement, similar phenomena occurred. When a stationary grating was superimposed on a drifting grating the MAE was depressed and perceived velocity increased when the spatial frequeny of the stationary gating was in the neighbourhood of, but above, that of the drifting grating. Both with spatial and temporal interruption an increase of perceived velocity accompanies MAE reduction. A number of interesting special phenomena were observed. One of these was the difficulty of observing the direction of movement of a grating drifting behind a narrow aperture. Another was the perceptual fluctuations which occur when a stationary grating is superimposed on a moving grating. Beat-waves drifting in the opposite direction to the moving gating were also seen with these as well as induced positive MAEs. It was concluded that the difference between the effect of temporal and spatial interruption on the MAE reflected fundamental differences between the visual processing of temporal and spatial dimensions. However, the increase of perceived velocity with temporal interruption suggests that some kind of frequency analysis is involved in visual movement perception as well as in spatial perception. The increase in perceived velocity with spatial interruption indicates that the processing of spatial and temporal frequency is interdependent.