A model for adaptation-level effects on stimulus generalization.

Shifts in Postdiscrimination Gradients Within a Stimulus Dimension Based on Female Waist-to-Hip Ratios

“…However, the present results are consistent with other investigations of gradient shifts in humans, which have shown that it is not uncommon for the area under the gradient to shift while the modal response remains unchanged (e.g., Derenne & Breitstein, 2006;Galizio, 1985;O'Donnell, Crosbie, Williams, & Saunders, 2000;Spetch et al, 2004;Thomas, Windell, Williams, & White, 1985). The degree of shift that occurs may be affected by a number of variables not presently under consideration, such as the preexperimental learning history of the individual and the manner in which the generalization test is performed (see Thomas, 1993, for a review). Therefore, the present findings do not preclude the possibility that more dramatic effects might occur in differently designed studies or in nature.…”

“…principally through laboratory-based research on generalization within sets of unidimensional stimuli (for reviews, see Honig & Urcuioli, 1981;Rilling, 1977;Thomas, 1993). Nevertheless, a number of authors use these terms (especially peak shift) to describe processes involved in judgments of complex stimuli in the natural environment.…”

Discrimination and generalization along a simple dimension: Peak shift and rule-governed responding.

“…In fact, other techniques for assaying post-discrimination generalization, most notably absolute identification procedures (i.e. using same/different judgements) have, on the whole, also failed to provide unequivocal demonstrations of peak shift on simple stimulus dimensions, at least in the absence of strongly biased test ranges (see, for instance, Thomas, 1993). The results of Experiments 1 and 2 are therefore particularly interesting in that they yielded true peak shift effects in the initial stages of testing that cannot readily be attributed to changes in adaptation level (Thomas, 1993) or other explanations associated with biased test ranges.…”

“…This assumption forms an integral part of some theories of discrimination learning based on comparison with a decision criterion, such as Thomas' (1993) particular variant of Adaptation Level theory. In most of the experiments cited above, the training stimuli were sufficiently different to be easily distinguishable from one another from the outset.…”

The learning of basic-level categories by pigeons: The prototype effect, attention, and effects of categorization

“…The magnitude of the response strength to P+ depended on the test stimulus sets-an effect similar to the response range effect; the location of the peak of responding depends on the range of stimuli used in testing. Response range effects have been found in humans (Thomas, 1993(Thomas, , 1994 and explained by Thomas (1993) on the basis of Helson's (1964) adaptation-level theory. Given that the test stimuli appearing during the FC test are more physically similar to the training exemplars than are those appearing during the NC test, the present finding is consistent with the notion applied to the response range effects.…”