Abstract
The method of constant stimuli is unreliable, because it causes an unpredictable constant error. An explanation of the constant error in terms of adaptation-level theory implies that the point of subjective equality changes with time. When the method of constant stimuli was used, the constant error was present from the first response and did not change substantially with time, thus indicating that an explanation in terms of an adaptation level is implausible. A modified version of the method of single stimuli was also used, in which observers had to estimate the magnitude of the length of both lines in a pair. The use of a direct method produced a reversal of the direction, and a substantial reduction in magnitude, of the constant error.
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I wish to thank M. Teghtsoonian and G. Vicario for comments, and S. Bettella for help in cross-checking the microcomputer programs.
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Masin, S.C. Different biases in the methods of constant and single stimuli. Bull. Psychon. Soc. 25, 379–382 (1987). https://doi.org/10.3758/BF03330373
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DOI: https://doi.org/10.3758/BF03330373