Anisotropy for direction discrimination in a two-frame apparent motion display.

Direction discrimination (upward/downward or left/right) for a Gabor patch in a two-frame motion display was measured as a function of the inter-frame displacement size of the component grating with the stimulus position (center, left, right, upper and lower visual fields) as a parameter. The results showed that, for vertical motion in the center, left, right and lower visual fields, the observers saw downward motion more frequently than upward motion, whereas for vertical motion in the upper field and for horizontal motion, no preference for one of the two opposite directions was obtained. Human motion vision is anisotropic in the lower half of the visual field.