Abstract

We present psychophysically based estimates of the relative numbers of L to M cones as a function of retinal eccentricity using the methods¹ which we previously applied to the fovea. Parafoveal detection data of three trichromatic observers were used to obtain estimates of this ratio at retinal eccentricities of 0.5, 1.0, 2.0, and 4.0°. The probability of detection functions was measured for a small (2.0-6.0-min) brief (50-ms) monochromatic red test on a green background and a monochromatic green test on a spectrally mixed violet background. These conditions were selected to provide L and M cone isolation in addition to eliminating the contributions of the rods and short-wavelength-sensitive cones. Ratios were obtained in two ways: (1) by using our model to obtain best-fitting theoretical functions and (2) by comparison of the slopes of the psychometric functions. The mean L to M cone ratio was 2.10 at 0.5° and 1.99 at 1.0° eccentricity. The ratio obtained at 0.5 and 1.0° did not significantly differ from the ratio obtained in the fovea for each observer. These results indicate that the L to M cone ratio remains stable from 0 to 1.0° in the temporal retina. Our estimates of the density of cones (L + M) show a decline with eccentricity which is in good agreement with anatomical studies.

© 1987 Optical Society of America