Distance effects on sequential dependencies in categorical judgments

Two forms of sequential dependency have been found in an auditory identification experiment: assimilation produced by the previous response and contrast caused by the preceding stimulus. The strength of these phenomena partly depends on the distance between stimuli and responses. For example, the strength of assimilation brought about by the previous response decreases with increased separation between successive stimuli. An inverse distance effect was observed for contrast caused by the preceding stimulus, which is equivalent to that found in the case of contrast produced by extraserial anchors. Observed response probabilities exhibit complicated dependencies on the current stimulus and the previous response that are not explained by existing models. An alternative model is suggested that is capable of accounting for these dependencies and for the distance effects. This model contains two mechanisms to explain sequential dependencies: The trace of the preceding stimulus acts as an internal standard, and the previous response influences a guessing strategy.