Abstract
The visual system initially collects spatially localised estimates of motion and then needs to interpret these local estimates to generate 2D object motion and self-motion descriptions. Commonly sinusoidal gratings have been employed to study the perception of motion and while these stimuli are useful for investigating the properties of spatial- and temporal-frequency tuned detectors they are limited. They remove textural and shape cues that are usually present in natural images, which has led to models of motion processing that ignore those cues. However, the addition of texture and shape information can dramatically alter perceived motion direction.
Recent work has shown that orientation-tuned simple cells are stimulated by moving patterns because of their extended temporal integration. This response (sometimes called motion streaks) allows orientation-tuned detectors to contribute to motion perception by signalling the axis of motion. The orientation cue is influential even if second-order streaks which could not have been produced by image smear are employed. This suggests that any orientation cue may be used to determine local direction estimates: a view that is extended to argue that aperture shape itself may have an impact by providing orientation cues which are incorporated into the direction estimation process. Oriented textural cues will also be shown to distort direction estimates, even though current models suggest they should not. The conclusion is that pattern information has a critical role in early motion processing and should be incorporated more systematically into models of human direction perception.