The cyclopean ternus display and the perception of element versus group movement

This study investigated the perception of bistable stroboscopic motion (Ternus display) with cyclopean stimuli created from retinal disparity embedded in dynamic random-element stereograms, the responses to which arise at binocular-integration levels of the visual system. To provide comparison data, observers were also tested with luminance-domain stimuli matched as closely as possible to their cyclopean counterparts. The results showed that the perception of element vs group movement was similar for both stimulus domains: element movement predominated at short interstimulus intervals (ISIs) while group movement predominated at long ISIs, and there was a tendency for a greater percentage of group movement to occur with a longer frame duration. These results cast suspicion on the interpretation of bistable motion that assumes element movement is a signature of a lower-level, short-range motion system whereas group movement is a signature of a higher-level, long-range system; both percepts are engendered at binocular-integration levels of vision.