Cyclovergence with Isoluminant Stimuli.

Karl Frederick Arrington,
Byron J. Pierce

Perception 1998; Vol. 27 Suppl., p. 137.
European Conference on Visual Perception (ECVP),
Oxford, England, 24-28th August 1998.

We studied the effects of isoluminant stimuli on the cyclovergence mechanism. Some previous studies report that stereo depth perception is compromised at isoluminance. Other studies report that rotation disparities affect ocular torsion, which affects perceived inclination of stereo images. We measured the effects of presentation duration and luminance-contrast, across the isoluminance point, of a red, zero-disparity pattern (R0) against a dim green background, on the perceived inclination of a superimposed, high luminance-contrast, green, 4 deg rotation-disparity pattern (G4). Each stereo image included two arrays (R0 & G4) of randomly distributed texture elements (crosses, squares, etc.) subtending 53H x 43V-deg visual angle, which yielded two depth planes. The luminance of the red, R0-plane was randomly varied. Presentation duration varied between 2- and 12-sec and the perceived inclination of the G4 pattern was measured. At 2-sec duration, the inclination function was almost level at about 16 deg, across all red luminance levels. At 7-sec duration, a gradual change in inclination indicated a decreasing effect of R0 as it approached isoluminance, with a sharp compromise directly at the isoluminant point. At 12-sec duration, the area of gradual inclination-change widened and also deepened to near the maximum level at 7-sec. Isoluminance clearly affected relative inclination of R0 and G4, from which we infer reduced stimulation to the cyclovergence system. The widening and deepening of the para-isoluminance area indicate a strong temporal integration component to isoluminant stimulus effects in the visual system. Apparently, the magnocellular channel is dominant in cyclovergence control.

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