Our perception is a part of reality.

Amir H. Ghaseminejad, 29 February 2012



Helson (1947), adaptation-level theory posits that one’s judgment or evaluation of an outcome is a function of all the previously experienced outcomes. In particular, the theory expresses the relationship mathematically by proposing that one’s adaptation level, or reference point for subjective judgments, is the logarithm of the mean of relevant stimuli, where individuals weight such stimuli based on their recency and salience among other criteria. In this sense, adaptation-level theory is a psychological theory of relativity based on the general principle of perceptual contrast where any subjective judgment is influenced by the prevailing norm or adaptation level. The theory also suggests that individuals continually adapt to label the existing level of any stimulus as the norm.

A theory positing that an individual’s reference point for subjective judgments regarding particular classes of stimuli is determined by the individual’s prior exposure to such stimuli as well as recollections of past judgments of similar stimuli.

While adaptation-level theory has been formulated in precise mathematical terms, it also provides a basis for non-mathematical application. For example, the theory can be used to explain why an individual may see a new car model of a particular size and consider it to be ‘big,’ as it would be judged in relation to the individual’s perception of the prevailing norm for new car model size, yet, given a case where most new car models become bigger over time, the individual’s reference point for car size judgments will shift to that of a bigger size. Marketers should therefore seek to understand how a consumer’s judgment is influenced by his or her prior exposures to related stimuli in order to explain and predict better such judgments. Such knowledge can therefore provide the marketer with insights into appropriate marketing  communications or persuasive messages that may be aimed at altering or influencing such consumer judgments.

A theory proposed by the US psychologist Harry Helson (1898–1977) in an article in the American Journal of Psychology in 1947, according to which the adaptation level is determined for a class of stimuli by members of the class already sampled or attended to, by stimuli having a background or contextual influence, and by recollections of past judgements of similar stimuli, the adaptation level being the logarithm of the mean of the relevant stimuli, weighted according to their effectiveness in terms of nearness, recency, salience, and so on. According to the theory, subjective judgements are necessarily relative to the prevailing norm or adaptation level, so that a 4 ounce (113 gram) pen is heavy, but a baseball bat must weigh over 40 ounces (1.13 kilograms) to be judged heavy. The phenomenon is a type of context effect. Also called AL theory. See also hedonic treadmill, prospect theory. Compare assimilation-contrast theory.