Perceptual motion standstill in rapidly moving chromatic displays

In motion standstill, a quickly moving object appears to stand still, and i ts details are clearly visible. It is proposed that motion standstill can o ccur when the spatiotemporal resolution of the shape and color systems exce eds that of the motion systems, For moving red-green gratings, the first- a nd second-order motion systems fail when the grating is isoluminant. The th ird-order motion system fails when the green/red saturation ratio produces isosalience (equal distinctiveness of red and green). When a variety of hig h-contrast red-green gratings, with different spatial frequencies and speed s, were made isoluminant and isosalient, the perception of motion standstil l was so complete that motion direction judgments were at chance levels. Sp eed ratings also indicated that, within a narrow range of luminance contras ts and green/red saturation ratios, moving stimuli were perceived as absolu tely motionless. The results provide further evidence that isoluminant colo r motion is perceived only by the third-order motion system, and they have profound implications for the nature of shape and color perception.