On the perception of relational motion

Six experiments were performed to examine the adequacy of detection/computation models for understanding the perception of relational motion, and in particular, the perception of three-dimensional motion in two-dimensional displays. The stimuli were a pair of dots which moved relationally (i.e., the relative location of the dots changed). Three-dimensional motion was seen when a contraction of the stimulus preceded an expansion (i.e., the dot separation first decreased, then increased), the angular difference between the pattern orientation and the direction of movement was small, and the spatial separation between dots was small. Neither the activation of higher-order, relational feature detectors, nor the construction/computation of relational motion from the detected motion of individual dots, can adequately explain the perception of three-dimensional motion.