Spatial determinants of depth perception in two-dot motion patterns

The aim of the present study was to identify spatial properties of motion patterns yielding perceived depth. A model was proposed to describe the different motion patterns in terms of the common and the relative motions of the moving parts. Using motion patterns consisting of two dots moving in straight paths, it was found that there were three different types of relative motions yielding unambiguous percepts: (1) lack of relative motions was perceived as motion in a frontoparallel plane; (2) two-dimensional concurrent motions were perceived as translatory motion in depth; (3) nonconcurrent motions were perceived as rotation in depth. Only two-dimensional motion patterns yielded stable depth percepts. The utility of the proposed vector analysis was discussed, and further research suggested.