Showing papers by "Stuart Anstis published in 1987"

Equiluminance: spatial and temporal factors and the contribution of blue-sensitive cones.

Abstract: Equiluminance ratios for red/green, red/blue and green/blue sine-wave gratings were determined by using a minimum-motion heterochromatic matching technique that permitted reliable settings at temporal frequencies as low as 0.5 Hz. The red/green equiluminance ratio was influenced by temporal but not spatial frequency, the green/blue ratio was influenced by spatial but not temporal frequency, and the red/blue ratio was influenced by both. After bleaching of the blue-sensitive cones, there was no change in equiluminance ratios, indicating no contribution of the blue-sensitive cones to the luminance channel even at low temporal and spatial frequencies. The inhomogeneity of yellow pigmentation within the macular region was identified as the source of the spatial-frequency effect on the blue/green ratio.

Optokinetic technique for measuring infants’ responses to color

Abstract: Two motion tests will measure normal and defective responses to color in non-verbal infants. Moving gratings displayed on a computer-controlled TV monitor elicited optokinetic eye movements. The first test established three results. First, non-verbal infants can be successfully screened, the one baby known to be colorblind was readily identified. Second, the equiluminance point for red and green was shifted for protans, who needed more red light than normals to make an equiluminance match. Third, the relative contribution of R- and G-cones to the luminance pathways is already in place at the adult level within the first three months of life. The second test, run only on adults, correctly diagnosed deutans who were missed by the first test, and showed that opponent-color mechanisms contribute directly to motion for normal but not for color-deficient observers.

Magnification factor for adaptation of a visual transient mechanism.

Abstract: After adaptation by an observer to a patch of gradually increasing (or decreasing) luminance, a steady test patch appeared to be gradually dimming (or brightening). These aftereffects did not transfer interocularly. Adaptation to a checkerboard, in which the white squares gradually dimmed while the black squares gradually brightened, gave an aftereffect that was a pattern of intersecting diagonal lines, that is, an extremely blurred checkerboard. The larger the squares of the checkerboard were, the farther into the periphery the aftereffect extended, because small squares were blurred out by the summation areas of the underlying visual channels, which were larger at increasing eccentricities and had diameters of 20 times the resolvable dot separation. The estimated visual acuity of these channels was as low as 20/400. These estimates were confirmed by manipulating separately the local and space-averaged luminances of the adapting stimulus.