Action and attentional load can influence aperture effects on motion perception.

When a moving featureless contour is viewed through a stationary circular aperture that occludes the contour's endpoints and the contour moves in a direction non-parallel to its orientation, observers report the contour's direction of motion as perpendicular to the contour's orientation regardless of its actual direction. In typical studies of this aperture effect on motion perception, observers made perceptual judgments of the line's motion. The aperture effect was not measured when observers actively controlled the line's motion. In addition, effects of attentional load on the aperture effect were not measured. Here, we demonstrated that attentional load influenced the aperture effect. Active control reduced the aperture effect, but did not eliminate it. Results have theoretical implications for motion perception and practical implications for the design of technologies that limit an observer's field-of-view such as surgical cameras.