Abstract
Previous studies have found large misperceptions when subjects are reporting 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 present, we reassessed these earlier measurements taking into account recent findings about directional misperceptions affecting the perception of single motion (reference repulsion). While our measurements confirm that errors in directional judgements of transparent motions can indeed be as big as 22° we find that motion repulsion, i.e. the interaction between two directions, contributes at most about 7° to these errors. This value is comparable to similar repulsion effects in orientation perception and stereoscopic depth perception, suggesting that they share a common neural basis. Our data further suggest that fast time scale adaptation and/or more general interactions between neurons contribute to motion repulsion while tracking eye movements play little or no role. These findings should serve as important constraints for models of motion perception.
Highlights
When subjects are asked to estimate the direction of one of two spatially superimposed dot patterns or gratings moving at an acute angle they tend to misperceive the angle formed by the two directions
The average across these four measurements for all subjects was a misperception of only 7.1° (93.4°, 99% confidence interval). This value is not significantly different from the 10° estimate for true motion repulsion in the previous experiment and reinforces our interpretation that the misperception exceeding 20° in the Sekuler and Marshak experiment was a combination of motion repulsion and reference repulsion
Using the previous experiment as a starting point we investigated the effect of changing different parameters on the amount of motion repulsion
Summary
When subjects are asked to estimate the direction of one of two spatially superimposed dot patterns or gratings moving at an acute angle they tend to misperceive the angle formed by the two directions This phenomenon of motion repulsion between visual directions has been amply documented (Levinson & Sekuler, 1976; Marshak & Sekuler, 1979; Mather & Moulden, 1980; Burke & Wenderoth, 1993; Hiris, 1995; Qian & Geesaman, 1995; Hiris & Blake, 1996; Kim & Wilson, 1996; Wishart, Braddick & Curran, 1998). The influence of various stimulus parameters on this true motion repulsion is investigated in an effort to understand the underlying mechanisms of this misjudgment
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