SUCCESSIVE EPISODES PRODUCE DIRECTION CONTRAST EFFECTS IN MOTION PERCEPTION

Motion coherence thresholds decline with an increase in the number of frames in a random dot kinematogram (RDK), indicating that motion info rmation can be integrated across successive frames. We investigated wh ether such temporal integration would be disrupted by a brief interval (32-600 msec) inserted into a motion sequence, perceptually dividing it into two successive episodes. Both episodes consisted of only a few frames (between 3 and 15), with the first episode being 100% coherent and the coherence of the second episode being adjusted to determine t hreshold. In four experiments we observed that coherence threshold for motion in the second episode was elevated if the directions in the tw o episodes matched, was lowered if they were opposite, and was unaffec ted if they were orthogonal. This successive direction contrast effect did not vary with the duration of the interval, suggesting that it is not an adaptation effect. The result of varying the number of frames in the second episode suggests that these effects are not due to alter ations in cooperative activity among motion detectors. We suggest that successive direction contrast effects may reflect activity of higher- order perceptual organization mechanisms. (C) 1998 Elsevier Science Lt d. All rights reserved.