Detection and discrimination of moving stimuli: the effects of color, luminance, and eccentricity

Psychophysical detection and direction discrimination thresholds for 1c/o, 1-Hz Gabors are plotted in a Weberian long-middle-wavelength-sensitive cone contrast plane. The shape of these threshold contours suggests linear cone contributions to additive (delta L/Lb + delta M/Mb) and opponent (delta L/Lb - delta M/Mb) postreceptoral mechanisms. The opponent mechanism dominates thresholds at the fovea, but sensitivity decreases rapidly with eccentricity in comparison with the additive mechanism. Cone contributions to the mechanisms vary in a small and nonsystematic manner across the retina. The experiments show that the additive mechanism is directionally sensitive at detection threshold. At all eccentricities studied (0-24 degrees), 0.3-log-unit suprathreshold contrasts are necessary for the opponent mechanism to signal direction of motion.