THE EFFECT OF COMPLEX MOTION PATTERN ON SPEED PERCEPTION

We recently reported a new motion illusion where dots in expanding ran dom dot patterns appear to move faster than those in rotation patterns despite having the same physical speed distributions. In the current paper, we compared expansion and rotation motion to translational moti on and found that the perceived dot speed in translation patterns was between that of expansion and rotation. We also explored contraction m otion and found subjects perceived dots in contracting patterns as mov ing slightly faster than those in expanding patterns and much faster t han those in rotating patterns. Finally, we found that stimulus presen tation order in a trial plays an important role in determining the mag nitude of the speed illusion - the effect is greater when the subjecti vely faster stimulus is viewed second (e.g., expansion after rotation) . The dependence on stimulus order is greatest when comparing complex motion patterns with large subjective speed differences. This phenomen on is unlikely to be explained in terms of channel fatigue or adaptati on. (C) 1998 Elsevier Science Ltd. All rights reserved.