Comparing motion induction in lateral motion and motion in depth

Induced motion, the apparent motion of an object when a nearby object moves, has been shown to occur in a variety of different conditions, including motion in depth. Here we explore whether similar patterns of induced motion result from induction in a lateral direction (frontoparallel motion) or induction in depth. We measured the magnitude of induced motion in a stationary target for: (a) binocularly viewed lateral motion of a pair of inducers, where the angular motion is in the same direction for the two eyes, and (b) binocularly viewed motion in depth of inducers, where the angular motions in the two eyes are opposite to each other, but the same magnitude as for the lateral motion. We found that induced motion is of similar magnitude for the two viewing conditions. This suggests a common mechanism for motion induction by both lateral motion and motion in depth, and is consistent with the idea that the visual signals responsible for induced motion are established before angular information is scaled to obtain metric motion in depth.