Abstract

Psychophysical detection and direction discrimination thresholds for 1c/°, 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 (ΔL/Lb + ΔM/Mb) and opponent (ΔL/Lb – ΔM/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°), 0.3-log-unit suprathreshold contrasts are necessary for the opponent mechanism to signal direction of motion.

© 1994 Optical Society of America

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