Interaction of Multiple Surface Cues in Motion Grouping
A rotating ellipse and a translating ogive may appear rigid or nonrigid depending on their shapes. By placing moving dots (‘satellites’) in the space surrounding the contour one can cause the percept to switch between rigid and nonrigid, depending on how the dots move. We have studied how multiple surface cues can influence this grouping effect. One set of displays consisted of the ambiguous contour and a group of consistently moving satellites. We found that under this condition the grouping was extremely robust. The influence of the satellites on the perceived rigidity of the contour remained powerful when they were moved far away from the contour and even when they were placed at a different stereoscopic depth plane. A second set of displays consisted of the ambiguous contour and two groups of satellites: one group moving rigidly and the other nonrigidly. In these displays we found a strong effect of stereo and distance. One could cause the percept to switch from rigid to nonrigid by manipulating the relative distances of the display elements or the relative disparities. We discuss how these results can be accounted for in a computational model that combines form and motion information in a robust estimation framework.