Estimation of the L-, M-, and S-cone weights of the postreceptoral detection mechanisms

Abstract

We have obtained two- and three-dimensional detection threshold contours in cone contrast space for sinusoidal gratings for three subjects at three spatiotemporal conditions (1 cycle/degree (c/deg), 0 Hz; 0.125 c/deg, 0 Hz; 1 c/deg, 24 Hz). These conditions were chosen to favor the response of each of the three postreceptoral mechanisms in turn. Contours were obtained from measurements in as many as 60 axes in (L, M, S) cone contrast space and were fitted by superellipses. Our technique permitted us to improve on earlier estimates of the cone weightings to the mechanisms. We found that the red–green mechanism has an input cone weighting of L−M with a 2% S-cone input; the luminance mechanism has a weighting of kL + M, where k varies between 3 and 5 at the high-temporal condition, with a 5% S-cone input in opposition to L- and M-cones; and the blue–yellow mechanism consists of S inputs in closely balanced opposition to L and M inputs. These cone weights were found to be consistent among our three subjects.