EFFICIENCY IN DETECTION OF ISOLUMINANT AND ISOCHROMATIC INTERFERENCE-FRINGES

We examined the limitations imposed by neural factors on spatial contr ast sensitivity for both isochromatic and isoluminant gratings. We use d two strategies to isolate these neural factors. First, we eliminated the effect of blurring by the dioptrics of the eye by using interfere nce fringes. Second, we corrected our data for additional sensitivity losses up to and including the site of photon absorption by applying a n ideal-observer analysis described by Geisler [J. Opt. Soc. Am. A 1, 775 (1984)]. Our measurements indicate that the neural visual system m odifies the shape of the contrast-sensitivity functions for both isoch romatic and isoluminant stimuli at high spatial frequencies. If we ass ume that the high-spatial-frequency performance of the neural visual s ystem is determined by a low-pass spatial filter followed by additive noise, then the visual system has a spatial band-width 1.8 times lower for isoluminant red-green than for isochromatic stimuli. On the other hand, we find no difference in bandwidth or sensitivity of the neural visual system for isoluminant red-green and S-cone-isolated stimuli.