Abstract
A moving object can induce an opposite direction of motion in a neighboring target, a phenomenon called induced motion. It has been suggested that motion induction is due to target-inducer interactions that are local in visual space. According to this view, increasing the distance between inducer and target should weaken induced motion. Alternatively, separation in depth per se may not determine whether one object can affect the motion of another. Currently available data supports either viewpoint. In particular, Gogel and Mac Cracken (1979) observed a strong weakening of induced motion as the target's location in depth moves farther than the inducer, whereas Di Vita and Rock (1997) noted that depth separation did not exert a strong influence. We noticed that the former study employed stimuli whose motion covered a constant visual angle across depth, whereas the second study employed a constant extent of motion on the stimulus display. Here we report the results of psychophysical experiments which leverage on this difference to resolve the discrepancy in the two results and show that disparity-based depth is insufficient to determine the strength of induced motion. Participants rated the effect of a horizontally oscillating inducer frame on a vertically oscillating target dot presented at different disparities in an otherwise dark environment. In the constant visual angle condition (similar to Gogel and Mac Cracken (1979)), induced motion decreased with depth separation. In the constant extent condition (similar to Di Vita and Rock (1997)), induced motion was constant across depth. These results imply that factors related to the target velocity or extent of motion, more than depth, determine the magnitude of motion induction. AY and JL are supported in part by CELEST, an NSF Science of Learning Center (NSF SBE-0354378). JL is also supported in part by the SyNAPSE program of DARPA (HR001109-03-0001, HR001-09-C-0011).
AY and JL are supported in part by CELEST, an NSF Science of Learning Center (NSF SBE-0354378). JL is also supported in part by the SyNAPSE program of DARPA (HR001109-03-0001, HR001-09-C-0011).