Revisiting motion repulsion: evidence for a general phenomenon?

Previous studies have found large misperceptions when subjects are reportin g the perceived angle between two directions of motion moving transparently at an acute angle, the so called motion repulsion. While these errors have been assumed to be caused by interactions between the two directions prese nt, we reassessed these earlier measurements taking into account recent fin dings about directional misperceptions affecting the perception of single m otion (reference repulsion). While our measurements confirm that errors in directional judgements of transparent motions can indeed be as big as 22 de grees we find that motion repulsion, i.e. the interaction between two direc tions, contributes at most about 7 degrees to these errors. This value is c omparable to similar repulsion effects in orientation perception and stereo scopic depth perception, suggesting that they share a common neural basis. Our data further suggest that fast time scale adaptation and/or more genera l interactions between neurons contribute to motion repulsion while trackin g eye movements play little or no role. These findings should serve as impo rtant constraints for models of motion perception. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.