Predicting color from gray: the relationship between achromatic adjustment and asymmetric matching

Achromatic adjustment has been used widely to study color context effects. In the achromatic adjustment procedure, an observer adjusts a test stimulus until it appears black, gray, or white. By its nature, achromatic adjustment directly measures the effect of context only for stimuli that appear gray. We present achromatic loci measured in two contexts and asymmetric color matches measured across the same two contexts. The results indicate that achromatic adjustments, together with a gain-control model, may be used to make accurate predictions of the chromaticity of asymmetric matches. Thus measurements of the effect of context for test stimuli that appear gray may be used to predict the effect of context for stimuli that appear colored. The experiments also indicate that accurate prediction depends on ensuring that observers use similar fixational strategies for the two judgments.