Apparent swinging motion from a 2-D sinusoidal pattern

A new motion illusion is reported that is observed on a 2-D sinusoidal patt ern composed of two I-D sinusoids, in which the constituent elements of the middle column appear to swing relative to the two flanking columns when th e point of fixation is slowly moved back and forth about the middle column. To better understand the underlying mechanisms of the apparent swinging mo tion, the spatial properties of a 2-D sinusoidal pattern were examined in t erms of spatial frequency, orientation, and contrast. Thirty-four subjects rated the magnitude of the motion. The apparent swinging was greatest when the two I-D components had spatial frequencies of 1-2 cycles deg(-1), relat ive orientations between 15 degrees and 30 degrees, and high contrasts. A s patiotemporal interaction between spatially overlapping visual units differ ing in polarity (Khang and Essock, 1997 Perception 26 585-597, 831-846) and the resultant shift in the global-motion signal was proposed as a likely c ause of the apparent swinging motion.