Prototypicality and deductive reasoning

It is hypothesized that people use formally incorrect deductive procedures, and this is sometimes advisable. The particular “prototypicality heuristic” investigated is: to determine validity of a proof, (a) work out an example, and (b) pick a “good” rather than arbitrary example. An interaction was predicted between validity of inference and prototypicality of example. Experiment 1, although quite sensitive to “calibration” variables, does not reveal the interaction in reaction times. However, Experiment 2, in which subjects' time was limited, seems to elicit the interaction in subjects' first-trial confidence judgments; the explanation proposed is that subjects then decide they must shift to a “quick and dirty” heuristic. Experiment 3 provides some preliminary evidence that subjects' “metaheuristic” decision to use the heuristic does lower error rates.