Luminance and color contrast sensitivity and VEP latency in subjects with normal and defective binocularity

Luminance contrast sinusoidal gratings (spatial frequencies 1, 2 and 4 cycles/degree) were compared with the corresponding color contrasting patterns (along the protan, deutan and tritan axes) to see whether they demonstrated normal binocular function in humans, and distinguished between normals and persons with defective binocularity. Contrast sensitivity and transient pattern VEP latency (on-responses) were measured in normals (n = 11, median age 36, range 12-46 years) and subjects with no stereopsis (n = 6, median age 13, range 8-38 years). The normal group had significantly higher contrast sensitivity with binocular stimulation for all patterns except tritan contrast gratings of 2 and 4 c/deg. The stereo-deficient group showed no higher binocular contrast sensitivity for any pattern. Differences between groups were significant with all gratings of 4 c/deg, and also with protan and deutan contrast gratings of 2 c/deg. In the normal group, binocular VEP latency was significantly shorter than the monocular with protan contrast gratings of 2 c/deg and tritan contrast gratings of 1 and 2 c/deg. Differences between the normal and the stereo-deficient groups were significant for all color contrast patterns of 2 c/deg; and tritan contrast gratings of 1 c/deg. We conclude that color contrast sensitivity and VEP measurements are potentially useful for demonstrating binocular function, and for separating normals from stereo-blind subjects. Color contrast patterns however are less effective than the corresponding luminance contrast patterns in evoking cortical potentials.