Effects of Trial Order on Contingency Judgments: A Comparison of Associative and Probabilistic Contrast Accounts

Four experiments examined trial sequencing effects in human contingency judgment. In Experiments 1-3, ratings of contingency between atarget cue and outcome were affected by the presentation rder of a series of trials distributed in2 distinct blocks and showed arecency bias. Experiment 4 replicated this effect when the trials were partly intermixed. These recency effects are predicted by an associative l arning model that computes associative strengths trial by trial and incorporates configural coding of cues but are problematic for probabilistic contrast accounts, which currently have no provision in the contingency computation for the differential weighting of trials as a function of their order of presentation. Humans and other organisms are very adept at judging whether and to what extent wo events are related. People can learn that pressing a light switch causes a light to come on, that eating a particular food makes them ill, that car accidents are more likely on wet roads, and a host of similar event relationships. A great deal of research interest has been recently dedicated to the study of how such judgments are made. In this article, we evaluate a theory of contingency judgment, recently formulated by Cheng and Holyoak (1995), which proposes that individuals compute event relationships in a normative fashion. In addition, the predic-tions made by this contingency theory are contrasted with those made by a completely different account of how event relationships are detected, namely an associative accoun