TEMPORAL AND CHROMATIC PROPERTIES OF MOTION MECHANISM

We measured threshold contours in color space for detecting drifting s inusoidal gratings over a range of temporal frequencies, and for ident ifying their direction of motion. Observers were able to correctly ide ntify the direction of motion in all directions of color space, given a sufficiently high contrast. At low temporal frequencies we found dif ferences between luminance and isoluminance conditions; for isoluminan ce there was a marked threshold elevation for identification when comp ared to detection. The threshold elevation for identification is depen dent on eccentricity as well as on temporal frequency. At high tempora l frequencies there were no differences between detection and identifi cation thresholds, or between thresholds for luminance and isoluminanc e. A quantitative analysis of the threshold contours allowed us to ide ntify two mechanisms contributing to motion: a color-opponent mechanis m with a high sensitivity at low temporal frequencies and a luminance mechanism whose relative sensitivity increases with temporal frequency . An analysis of the cone contributions to motion detection and identi fication showed that L-cones dominated threshold behavior for both det ection and identification at high temporal frequencies. There was a we ak S-cone input to motion detection and identification at high tempora l frequencies.