Complex Motion: Standstill and Motion Capture Illusions

A series of illusions were created by presenting stimuli in which some visual information (i.e. depth or color) is in complex motion (rotating, expanding, contracting or shearing) while some other visual information (i.e. luminance texture) is stationary or vice versa. When the luminance texture is stationary, an observer either perceives or fails to perceive complex depth or color motion (success or failure of motion transparencygiving rise to motion standstill). When the luminance texture is in complex motion, an observer either perceives the depth or color information as stationary (motion transparency) or as moving in synchrony with the luminance texture (failure of motion transparency resulting in motion capture). Here we demonstrate the existence of stereo rotation, expanding or contraction standstill and capture illusions ans stereo shearing standstill and capture illusions. We also demonstrate the existence of color complex motion standstill and capture illusions. Unlike as in stereo vision, color complex standstill and capture illusions occur only for stimuli with smooth transitions, but not for color stimuli with sharp transitions between their colors.

Taken together, these illusions are consistent with the hypothesis that complex motion is processed in a common pathway to which the putative feature tracking stereoscopic or chromatic motion system has no access. The main input to the complex motion pathway originates from a first order (velocity based) luminance motion pathway.

With regards to color vision, additional evidence was found for the existence of two separate color motion systems: i) A feature tracking system for isoluminant chromatic stimuli moving at low to medium speeds with smooth transitions between their colors. ii) A velocity based first order system both for luminance and chromatic stimuli with sharp transitions between their colors feeding into a common complex motion pathway.