Contribution of bottom-up and top-down motion processes to perceived position.

Perceived position depends on many factors, including motion present in a visual scene. Convincing evidence shows that high-level motion perception--which is driven by top-down processes such as attentional tracking or inferred motion--can influence the perceived position of an object. Is high-level motion sufficient to influence perceived position, and is attention to or awareness of motion direction necessary to displace objects' perceived positions? Consistent with previous reports, the first experiment revealed that the perception of motion, even when no physical motion was present, was sufficient to shift perceived position. A second experiment showed that when subjects were unable to identify the direction of a physically present motion stimulus, the apparent locations of other objects were still influenced. Thus, motion influences perceived position by at least two distinct processes. The first involves a passive, preattentive mechanism that does not depend on perceptual awareness; the second, a top-down process that depends on the perceptual awareness of motion direction. Each contributes to perceived position, but independently of the other.