SIMILARITY IN STIMULUS MATERIAL AND STIMULUS TASK ON THE FORMATION OF A NEW SCALE OF JUDGMENT

Two empirical tests of informal predictions from Helson's adaptation-level theory

Two experiments on adaptation-level theory are reported which arise from informal predictions made by Helson (1964). They both involved interpolated anchors in comparative judgments, in order to avoid the sorts of response factors inherent in the category scaling technique normally employed in adaptation level studies. The first experiment indicated the operation of time error as interstimulus intervals are increased. The second showed that if the anchor stimulus is not judged it is less effective in producing contrast compared with when it is judged. In addition, response times and confidence ratings of judgments were shown to be potentially useful indices of differences in effectiveness among the various anchor stimulus levels used. The strong relationship between these two measures is discussed.

Adaptation-level theory and context effects on sensory judgments: perception for 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.