We report two studies investigating how naïve reasoners evaluate the probability that a conditional assertion is true, and the conditional probability that the consequent of the conditional is true given that the antecedent is true. The mental model theory predicts that individuals should evaluate the probability of a conditional on the basis of the mental models representing the conditional, and that evaluations calling for a greater number of models should be more difficult. It follows that the probability of a conditional should differ from the corresponding conditional probability. The results of the studies corroborated these predictions, and contrast with alternative accounts of naive evaluations of the probability of conditionals.

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On the Wason selection task with the Sharing-rule, there are three major response patterns; 1) to select those cards that detect resource-provider’s non-cooperation to in-group, 2) to select those cards that detect resource-provider’s failure to exclude out-group parasitism, and 3) to select the cards that detect both types of rule violation. We examined the relationship between the individual differences on the Sharing-rule Wason selection task and the participants’ general trust level. Results showed lower general trusters tended to select the cards that detect resource-provider’s failure to exclude out-group parasitism. The higher general trusters showed a tendency to select only the cards that detect non-cooperation by resource-provider. These results suggest that individual differences on social rule reasoning are related to respondents’ perception, cognition, and attitude towards the social world.

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This study examined young children’s (N=87) development of conditional reasoning competence. Using the four-cards selection task of Harris and Nunez (1996), an age (3-, 4- and 5-year-olds) by context (deontic context whereby mother states the premise vs. descriptive context whereby the child states the premise) by task (familiar task based on a premise relating to an empirical matter for the participant vs. counterfactual task involving a counterfactual matter) factorial design (one between, two within factors) was utilized. According to the results, five-year-old children performed better than 3-year-olds, the deontic context encouraged children’s performance more than the descriptive context, and the counterfactual task was more difficult than the familiar task. A significant 3-way interaction showed that 5-year-olds could succeed even on the counterfactual task if it was in the deontic context. The data suggested that a theory of deontic reasoning was more appropriate than that of pragmatic reasoning model.

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Whether performing a syllogistic reasoning task (SRT) affects emotional state in different prior moods was tested using eighty participants in either a positive, negative, or neutral mood. A film mood induction procedure (MIP) was used and affective state was assessed before the MIP, after the MIP and after the SRT. The affective reactivity hypothesis – that personality influences the magnitude of affective change to an MIP – was also tested by having participants fill out the Eysenck Personality Inventory. Participants in a positive, but not in a negative or neutral, prior mood moved more negative after the SRT. Participants’ pattern of affective reactivity partly replicated previous research but contrary to prediction in the positive condition extraversion was inversely related to increases in positive (in the MIP) and negative (in the SRT) affect. These results suggest that, under some conditions, people may adaptively move to the mood-state that is most conducive to the type of cognitive task they must perform.

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The Representational Theory of Mind, or RTM, is arguably the best hope for formulating a naturalistic theory of reasoning. According to RTM, thinking processes are implemented by kinds of computational processes that are purely constituted by the syntactic relations of Mentalese symbols. But findings with the Wason selection task suggest that the appeal to syntactic or formal relations alone is not sufficient for understanding logical inferences. In order to understand logical inferences, one also has to understand the content effect that facilitates the inferential processes. Thus a satisfactory theory of reasoning requires a theory of thinking as well as a theory of content. But there is a problem of putting these two theories together. The aim of this paper is to highlight this problem.

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This experiment examined the relative merits of using within-and between-subjects designs to investigate deductive reasoning. Two issues were investigated: 1) the potential for expectancy and fatigue effects when using within-subjects designs, and 2) the relative power of within- vs between-subjects designs. Participants were presented with problems in a standard belief-bias paradigm in which the believability of putative conclusions varied orthogonally to their validity. The belief bias effect, as well as the effect of validity, and the interaction between beliefs and validity, were not affected by reasoners’ expectations regarding the number of problems they had to solve. The effect of beliefs and the belief by validity interaction were only marginally affected by the number of problems solved, despite adequate power to observe an effect. Thus, neither expectancy nor fatigue appear to have affected performance, suggesting that there are few drawbacks to using a within-subjects design. In contrast, however, a power analysis clearly established the desirability of using within- relative to between-subjects designs. Within-subjects designs require far fewer participants to detect effects of comparable size; this was especially true for higher-order (interaction) effects. Finally, we provide a power analysis of within- and between-subjects designs that should be of general utility to researchers planning studies using proportions as a dependent measure.

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