Figure 164

The percentage of subjects who solved Wason's selection task correctly in each condition as a function of provision of a rationale. Figure from Cheng and Holyoak "Pragmatic reasoning schemas" in Cognitive Psychology, Volume 17, 391— 416. Copyright © 1985 by Academic Press, reproduced by permission of the publisher.

called deontic reasoning (Manktelow & Over, 1991). All the realistic versions that facilitate reasoning use deontic forms rather than indicative forms of the conditional:

Indicative form: "If there is a p then there is a q"

Deontic form: "If you do p then you must do q"

The difficult abstract version of the task always has an indicative form of the rule whereas realistic versions have used deontic forms (but see Platt & Griggs, 1993, for further tests of this). For when the task is given in some deontic form then facilitation is found, even for abstract versions of the task. The crucial test was carried out by Cheng and Holyoak (1985) who gave subjects in Hong Kong and Michigan a version of the Johnson-Laird et al. postal problem and a variant about checking passengers' forms at an airport. The latter involved the testing of the following rule:

If the form says "ENTERING" on one side, then the other side includes cholera among the list of

Again, each problem had the appropriate P, Q, not-P, and not-Q cases. Neither group of subjects had direct experience of the airport problem, but the Hong Kong subjects were expected to be familiar with the postal rule. So, a memory-cueing hypothesis would predict that, on the airport problem, subjects in both Hong Kong and Michigan should be equivalent. However, Hong Kong subjects should do better than Michigan subjects on the postal version because of their prior experience. Cheng and Holyoak also gave half the subjects a rationale on both the postal and airport tasks. The stated rationale for the postal task was that a sealed envelope indicated first-class mail, for which the post office received more revenue; the rationale for the airport task was that a cholera inoculation was required to protect the entering passengers from the disease. The rationale casts the rule in a deontic light. Specifically, Cheng and Holyoak predicted that the rationale would cast the problems as a permission situation, in which some action/precondition must be carried out before another action is permitted, and that this would result in facilitation. As such, all subjects diseases.

should improve on both versions of the task (accepting that there may be a ceiling effect for the Hong Kong group on the postal task with the rationale).

Figure 16.4 shows the results of the experiment. They indicate that the memory-cueing hypothesis has some validity but is clearly not the whole story. The Hong Kong subjects did do better on the postal task with no rationale relative to the comparable Michigan group. However, irrespective of prior experience, all subjects produced uniformly high rates of correct responses when the rationale was provided. More conclusively, Cheng and Holyoak also found facilitation in performance for abstract materials, when the selection task was presented as an abstract description of a permission situation (i.e., If one is to take action A, then one must satisfy precondition P). Subjects in the abstract-permission version fared better (61% correct) than those in the usual version of the abstract task (19%). This finding is significant because such facilitation had never been observed for any other abstract version of the standard selection task (Jackson & Griggs, 1990). Although there has been some empirical questioning of these findings, the consensus seems to support the original result (see Evans, 1983; Girotto, Mazzocco, & Cherubini, 1992; Griggs & Cox, 1993; Kroger, Cheng & Holyoak, 1993).

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