Abstract
A coloured background may induce a contrasting colour in a figure set against it. We have previously shown that contrast induction may be suppressed by chromatic texture either in the figure or in its surround (ARVO, 2002). We now investigate the effects of varying the chromatic contrast of the texture, and of adding texture both to the figure and to its surround. A method of sequential presentation is used to estimate the change in colour appearance of a 1° square figure induced by changing the chromaticity of its background (30° x 20°). A neutrally coloured figure and background are presented initially for 0.5 s. The background chromaticity is then changed by a constant amount along the LM-axis, concomitant with a variable chromatic shift of the figure. After 0.5 seconds, a neutral mask is displayed and the observer signals whether the figure changed to become redder or greener. In different conditions, chromatic texture is added to the backgrounds and/or to the figures without changing their space-averaged chromaticity or luminance. Regular and irregular templates with spatial frequencies between 4 and 10 cpd. were used to generate textures with LM, luminance or S-cone contrasts. Induced contrast is measured as the amount of L-cone contrast that must be added to the figure to preserve its neutral appearance. We find that contrast induction in a textured figure is suppressed strongly even when the texture contrast is very low. This may explain why real-world objects, which are rarely uniformly coloured, do not normally change colour when set against different backgrounds. Contrast induction is less when texture is present in the figure only, than when it is present in both figure and background, despite the presence of more chromatic borders in the latter stimulus configuration. This result shows that contrast suppression cannot be due simply to the inability of contrast effects to propagate beyond these borders.
Supported by the Newcastle University Alumni fund.