Abstract

We created a class of stimulus that can be perceived unambiguously as either drifting to the left or right depending on the spatiotemporal configuration of their two defining attributes, i.e., color and orientation. Such stimuli permit the isolation of two distinct motion systems, a color-nonoriented (C) and a luminance-oriented (LO) one. The output strength of each of these mechanisms has been assessed as a function of the duration (number of frames) of the stimulus for short (15′) and long (1°) interframe displacements. Given that the stimulus attributes were identical in the two experimental conditions, this procedure allowed for a direct comparison of the motion output in the C and LO pathways. For short displacements C and LO outputs are of similar strength. Since it is known that luminance motion prevails over chromatic motion, it may be inferred that this difference is due to an imbalance between the motion outputs of the color-oriented and luminance-nonoriented channels. For long displacements, however, the C output is significantly stronger than the LO output, which is in line with previous results. When the spatiotemporal configuration of the stimulus is modified so that C and LO motion signals are simultaneously present and of opposite directions, C motion always prevails indicating C–LO inhibitory interactions.

© 1987 Optical Society of America