DIRECTION REPULSION IN MOTION TRANSPARENCY

A series of experiments investigated perceived direction of motion and depth segregation in motion transparency displays consisting of two p lanes of dots moving in different directions. Direction and depth judg ments were obtained from human observers viewing these ''bi-directiona l'' animation sequences with and without explicit stereoscopic depth i nformation. We found that (1) misperception of motion direction (''dir ection repulsion'') occurs when two spatially intermingled directions of motion are within 60 deg of each other; (2) direction repulsion is minimal at cardinal directions; (3) perception of two directions of mo tion always results in separate motion planes segregated in depth; and (4) stereoscopic depth information has no effect on the magnitude of direction repulsion, but it does disambiguate the depth relations betw een motion directions. These results are developed within the context of a two-stage model of motion transparency. On this model, motion dir ections are registered within units subject to inhibitory interactions that cause direction repulsion, with the outputs of these units poole d within units selective for direction and disparity.