PERCEPTION OF MOTION DIRECTION IN LUMINANCE-DEFINED AND CONTRAST-DEFINED REVERSED-PHI-MOTION SEQUENCES

Nonlinear processing can be used to recover the motion of contrast mod ulations of binary noise patterns. A nonlinear stage has also been pro posed to explain the perception of forward motion in motion sequences which typically elicit reversed-phi. We examined perceived direction o f motion for stimuli in which these reversed motion sequences were use d to modulate the contrast of binary noise patterns. A percept of forw ard motion could be elicted by both luminance-defined and contrast-def ined stimuli. The perceived direction of motion seen in the contrast-d efined stimuli showed a profound carrier dependency. The replacement o f a static carrier by a dynamic carrier can reverse the perceived dire ction of motion. Forward motion was never seen with dynamic carriers. For luminance- and contrast-defined patterns the reversed motion perce pt increasingly dominated, with increases in the spatial frequency and temporal frequency of the modulation. Differences in the patterns of responses to the two stimuli over spatial and temporal frequency were abolished by the addition of noise to the luminance-defined stimulus. These data suggest the possibility that a single mechanism may mediate the perception of luminance- and contrast-defined motion. (C) 1997 Pu blished by Elsevier Science Ltd.