Abstract
It is known that changes in direction of motion are perceived after changes in color when they occur synchronously. This illusion is explained on the basis of neural response latencies or by the faulty match between color and position transitions. Apparently, this asynchrony occurs only by the delay of perceived changes in direction of motion. The present study investigated to what degree detections of changes in direction of motion are delayed by detection and prediction tasks. Detection task: Plaid patterns were used as stimuli. Test patterns abruptly reversed color and direction of vertical motion synchronously and the observer quickly pressed a button to the reversal. The response time was measured as the detection time. Changes in color (no change, red to green, green to red) and direction of motion (downward to upward, upward to downward, no change) were variously combined. Detections of color-change were faster than those of direction-change to the same test patterns. Prediction task: Conditions for the number of alternations and temporal period of test patterns were added to those in detection task. After a test pattern alternated color and direction of motion synchronously, the pattern disappeared and the observer was asked to pressed a button when the temporal period of 1 Hz has passed. Prediction times for color-change were shorter than those for direction-change. The velocity effect was also observed in both tasks. These results seem to shed light on the causes of the illusion.