'Zigzag motion' goes in unexpected directions

Abstract

In a novel 'zigzag motion' display, random dots made alternate long and short jumps, 10 mm downward and 1 mm to the right. The zigs and zags were either at right angles (differing by 90 degrees) or in opposite directions (180 degrees). The perceived direction of motion varied with the viewing distance or spatial scale. During close-up [or distant] viewing the display appeared to move in the direction of the short [or long] jumps. When the motion was stopped after 30 s, a motion aftereffect (MAE) was seen, driven by the short jumps but not the long jumps. Therefore, the perceived direction of motion was dissociated from its aftereffect. A picture rotated alternately 5 degrees clockwise (CW) and 1 degrees counterclockwise (CCW) and appeared to rotate jerkily CW. When stopped, a clockwise MAE was seen, appropriate to the small 1 degrees jumps. If the test field contained blurred, dynamic visual noise, the MAE was now CCW, appropriate to the large 5 degrees jumps; the large jumps drove the perceived motion direction and dynamic MAE, but the small jumps drove the static MAE. Winner-take-all competition between pathways tuned to fast and slow movements. Their independent adaptation gave opposite static and dynamic MAEs.