Misinterpretation of conditional statements in Wason's selection task

Errors may be made on Wason's selection task because either (a) the rule to be tested is misunderstood, or (b) reasoning from that rule is inaccurate, or both. We report two experiments using the experimental paradigm introduced by Gebauer and Laming in which subjects are given six problems in succession. We use the subset of cards selected by each subject as (a) an indication of how the rule is understood and, when that selection is consistent throughout all six problems (so that we can infer a consistent understanding of the rule), as (b) a basis for evaluating the accuracy of the subject's reasoning according to three independent criteria. Experiment 1 adds an exactly parallel contextual version of the task to permit comparison between performances (by the same subjects) on the two versions. Experiment 2 repeats Exp. 1, but with negatives inserted in the conditional rule. Most subjects make a consistent selection of cards throughout all six problems, but typically appear to misunderstand the rule. This is so in both abstract and contextual tasks and replicates the finding by Gebauer and Laming. Most misunderstandings consisted of either (a) reading the simple conditional rule as a bi-conditional or (b) substituting "top/underneath" for "one side/other side". In Exp. 1 subjects seldom misevaluated the rule they appeared to be testing, but such "errors" of evaluation were common in Exp. 2. Negatives confuse the subjects and should not be used in any conditional application that matters. In Exp. 2 (but not 1) there was a significant correlation between interpretations of the two tasks. We provide an explanation of "matching bias" (it results from the confluence of the two common misunderstandings above) and comment on "mental models" which are, at present, unable to accommodate the variety of results we present here. We also relate our experimental paradigm to the conditional inference task and to truth tables.