Additional Twists on A Continuous Barber - Pole Illusion

The barber pole illusion is a well-known example of how the perceived direction of motion of an inherently ambiguous one-dimensional pattern is influenced by the shape of the area covered by the pattern. Similar effects may be observed for a stimulus which is restricted to a narrow band of spatial frequencies: when a sinusoidal grating is drifted behind a two-dimensional Gaussian contrast window having unequal standard deviations, the direction of perceived motion is biased in the direction of the major axis of the elliptical window (Mulligan, ARVO 1991). We have extended these results to provide insight into possible mechanisms responsible for the effect.