COLOR-LUMINANCE INTERACTION - DATA PRODUCED BY OBLIQUE CROSS MASKING

Threshold-elevation (TE-) versus-mask-spatial-frequency (SF) curves an d TE-versus-mask-contrast curves, produced by the oblique-masking tech nique, were reported for uncrossed stimuli (color-test-on-color-mask a nd luminance-test-on-luminance-mask) [Invest. Ophthahmol. Visual Sci. Suppl. 34, 751 (1993) and Vision. Res. 23, 873 (1983)]. The technique minimizes the artifacts that are due to spatial phase effects, spatial beats, spatial probability summation, and local cues. My goal was to measure these curves for crossed stimuli (color-test-on-luminance-mask and luminance-test-on-color-mask) by this oblique-masking technique a nd to compare the curves with those reported in previous studies. For this purpose threshold contrasts were measured by a yes-no procedure w ith randomized double staircases. Test targets were vertical spatially localized (D6) patterns, and masks were oblique sinusoidal patterns; both the test and the mask were presented simultaneously, for 2 s (Gau ssian window), on a color monitor interfaced with an ATVista system an d a Powell achromatizing lens. The test SF's were 0.125, 0.5, 2, 4, an d 8 cycles per degree (cpd); mask SF's were 0.031-16 cpd; and mask con trasts were 6.25%-50%. Furthermore, the Red-Green channel was defined by the minimum flicker and the hue cancellation techniques. Results sh ow mostly masking effect (TE > 1) at contrasts above threshold; someti mes, separability (TE = 1) and above-threshold facilitation (TE < 1) e ffects were also observed, depending on the test SF, the mask SF, the mask contrast, and the subject. In general, the magnitudes of TE's are smaller and the TE-versus-mask-SF curves are slightly narrower for th e oblique-cross-masking conditions than those for the respective obliq ue uncross masking. In addition, the TE-versus-mask-contrast curves fo r the crossed conditions are mostly shallower than those for the respe ctive uncrossed conditions. Furthermore, mostly the color-luminance as ymmetry (color masks luminance more than luminance masks color) is fou nd, in mild form, for SF's greater than or equal to 0.5 cpd. For the l ower SF of 0.125 cpd, there is either a lack of asymmetry or a very mi ld asymmetry of the opposite kind (luminance masks color slightly more than color masks luminance) seems to prevail. In general, the oblique -masking data shows mild asymmetry and reduced facilitation; both are consistent with reduced local cues, similar to those shown by randomiz ed phase data, thus making the data suitable for SF analysis; moreover , at high contrast, the masking data are consistent with those reporte d in previous studies. (C) 1998 Optical Society of America.