[Two-stimulus--two choice paradigm for psychophysics: range-frequency model and adaptation level theory in comparison]

The predictions provided by the range-frequency model and the adaptation-level theory were compared in respect of size judgments in an averbal two-category experiment. Squares of different sizes were presented in two different frequency distributions. After a two stimulus-two choice training, in which the subjects (N = 64) learned to which of the two response categories a relative small or large square belonged, a generalization context-series test followed. The two test series represented the two different frequency distributions used (the arithmetic mean was either smaller or larger than the median or midpoint). The percentage of large responses was registered. Furthermore, to investigate which experimental design would be appropriate for this research paradigm, the study was carried out using both a between-subjects and a within-subjects design. For the two experimental designs, the results pointed to a confirmation of the predictions provided by the adaptation-level theory (D. R. Thomas, 1993) but not the range-frequency model (Parducci, 1983, 1995).