Form-colour aftereffects: selectivity to local luminance contrast.

For long periods observers fixated low spatial frequency coloured gratings. Black and white test gratings of the same spatial frequency and orientation as the adapting gratings appeared coloured with the hue complementary to the adapting patterns when the dark test stripes fell on retinal areas previously occupied by the dark adapting stripes; no colour or very weak colour was seen when the test gratings were reversed in phase (contrast reversed). No colour aftereffects were produced with coloured gratings that lacked luminance contrast. The selectivity to the polarity of local luminance contrast can be explained by mechanisms that respond conjointly to colour and luminance contrast. The aftereffects are selective to spatial phase.