ANISOTROPIES IN VISUAL-MOTION PERCEPTION - A FRESH LOOK

We measured motion-detection and motion-discrimination performance for different directions of motion, using stochastic motion sequences. Ra ndom-dot cinematograms containing 200 dots in a circular aperture were used as stimuli in a two-interval forced-choice procedure. In the mot ion-detection experiment, observers judged which of two intervals cont ained weak coherent motion, the other interval containing random motio n only. In the direction-discrimination experiment, observers viewed a standard direction of motion followed by comparison motion in a sligh tly different direction. Observers indicated whether the comparison wa s clockwise or counterclockwise, relative to the standard. Twelve dire ctions of motion were tested in the detection task and five standard d irections (three cardinal directions and two oblique directions) in th e discrimination task. Detection thresholds were invariant with direct ion of motion, but direction-discrimination thresholds were significan tly higher for motion in oblique directions, even at low-coherence lev els. Results from control conditions ruled out monitor artifacts and i ndicate that the oblique effect is relative to retinal coordinates. Th ese results have broad implications for computational and physiologica l models of motion perception. (C) 1998 Optical Society of America.