Complex Motion: Standstill and Motion Capture Illusions

ccording to current experimental evidence a common neuronal pathway analyses complex motions (e.g. rotation, expansion/contraction, and shearing). Conflicting inputs from different modalities such as the luminance and the stereo system or the luminance system and the color system should result in motion capture or standstill illusions, if one of the conflicting inputs is suppressed. Otherwise, a percept of separate motion components arises. When probing the stereo-system using stereoscopic stimuli, where a rotating or expanding three-dimensional structure is encoded with a static random-dot texture, the perceived complex motion is dominated by the velocity of the overlying random-dot pattern, causing a “stereo complex motion standstill” at zero velocity and a “stereo complex motion capture” at higher speeds. When probing the color system using isoluminant red and green stimuli overlaid by random-dot pattern similar to the one used to produce the stereoscopic stimuli, the perceived complex motion is dominated by the overlaying dot texture resulting in “complex motion color standstill” or “color motion capture”, at low speeds. At higher speeds different outcomes were observed for either smooth or sharp transitions between red and green. While the perceived motion of smooth borders was still dominated by the dots’ motion, sharp borders are perceived as moving separately from the overlying dots. Similar results as with color border stimuli can be obtained with contrast-modulated random-dot patterns.