Exploration of the motion-induced position shift

Motion within a stationary object can cause spatially aligned images to appear shifted in their direction of movement. Some reports indicate that target detection at the leading edge of movement is easier when the target is in phase with its inducer, and detection declines with increasing distance between the inducer and target. These results suggest that the visual system extrapolates moving objects to compensate for perceptual delays. An alternative explanation is simple cell summation along the edge of the stimulus facilitates detection of inphase targets. The present study puts these explanations to the test. To differentiate them, target detectability was measured with varying contrast, phase alignment, distance, and motion in four experiments. The first two experiments replicated past results at the leading edge, but a novel effect was found: target detection at the trailing edge is also phasedependent. In the third experiment, using flickering motion as a control, phase again modulated detection. To further control for extrapolation, targets in the final experiment moved adjacent to the inducer, this was also modulated by phase. The results of these four experiments show that target detection is not only phase-dependent at the leading edge of motion - target detection also depends on phase at the trailing edge, adjacent to flicker, and adjacent to motion. These results support a simple cell summation explanation of the motioninduced position shift