DIFFERENT PARAMETERS CONTROL MOTION PERCEPTION ABOVE AND BELOW A CRITICAL DENSITY

The maximum displacement for the detection of apparent motion (D(max)) is measured using stimuli made up of Gabor function micro-patterns ra ndomly distributed across the stimulus field. Previous studies using h igh densities of micro-patterns have demonstrated D(max) to be depende nt on the spatial frequency content of the stimulus and not the size o f the stimulus elements. Here we report that D(max) increases suddenly when the number of micro-patterns in the visual field is reduced beyo nd some critical point. The number of micro-patterns at which the tran sition in D(max) occurs is found to be inversely proportional to the w idth of the micro-patterns along the axis of motion. Beyond this trans ition, for low density stimuli, D(max) is found to be dependent on bot h the number and size of micro-patterns in the stimulus field. These r esults are suggestive of the operation of different motion mechanisms under conditions of low vs high micro-pattern density.