Adaptation-Level Theory and Context Effects on Sensory Judgments: Perception or Response?

The evidence in favour of Helson's (1947, 1964) contention that context effects are the result of alterations in sensory excitability is reviewed. In particular Steven's (1958) criticism of category scaling, as a technique for establishing such context effects, is examined as well as the experimental evidence supporting it. These studies are not considered conclusive proof that such effects are solely mediated by response processes. Other evidence suggests that there is a perceptual component, and that therefore Helson's Adaptation Level Theory—a single factor theory—is probably oversimplified, since context effects appear to reflect a number of factors both perceptual and response based. The inappropriateness of analysing context effects by means of statistical decision theory is discussed.