Judged displacement in apparent vertical and horizontal motion
The judged vanishing point of a target traveling along a vertical or horizontal trajectory at uniform velocity was examined. In Experiments 1 and 2, subjects indicated the vanishing point by positioning a cross hair. Judged vanishing point was displaced forward in the direction of motion, and the magnitude of the displacement increased with the apparent velocity of the target. Displacement was greater for horizontal than for vertical motion. In Experiment 3, similar patterns were found using a forced-choice paradigm. Experiments 4 and 5 assessed the role of knowledge of the target’s likely behavior. In Experiment 4, the target bounced within the confines of a square frame. Judged vanishing point was displaced in the anticipated direction, even 9 when the anticipated direction was opposite to the current path of motion. Experiment 5 was a control experiment that ruled out the presence of the frame as the sole cause for displacement. The results suggest that displacement from the true vanishing point is due to a high-level cognitive mechanism capable of utilizing knowledge about probable target location.