Experiments are described which look for a ‘crispening effect’ in the hue domain. This effect—an enhanced discrimination around the adaptation level—has been shown for achromatic stimuli by both brightness scaling and contrast discrimination techniques (Whittle, 1992 Vision Research 32 1493 – 1507). In the present experiments these techniques are applied to chromatic variations along L(-M)L-cone and S-cone axes (MacLeod — Boynton isoluminant chromaticity space). Results so far support a crispening effect for the L(-M)-cone axis but not the S-cone axis. This enhanced discriminatory power in the vicinity of the background luminance and hue accords with the importance of relative, rather than absolute, values for coding by the visual system.
