The Analytic Truth and Falsity of Disjunctions

Disjunctive inferences are difficult. According to the theory of mental models, it is because of the alternative possibilities to which disjunctions refer. Three experiments corroborated further predictions of the mental model theory. Participants judged that disjunctions, such as Either this year is a leap year or it is a common year are true. Given a disjunction such as Either A or B, they tended to evaluate the four cases in its ‘partition’: A and B, A and not‐B, not‐A and B, not‐A and not‐B, as ‘possible’ or ‘impossible’ in ways that bore out the difference between inclusive disjunctions (‘or both’) and exclusive disjunctions (‘but not both’). Knowledge usually concerns what is true, and so when participants judge that a disjunction is false, or contingent, and evaluate the cases in its partition, they depend on inferences that yield predictable errors. They tended to judge that disjunctions, such as follows: Either the food is cold or else it is tepid, but not both, are true, though in fact they could be false. They tended to infer ‘mirror‐image’ evaluations that yield the same possibilities for false disjunctions as those for true disjunctions. The article considers the implications of these results for alternative theories based on classical logic or on the probability calculus.     

The Relation Between Factual and Counterfactual Conditionals

What is the relation between factual conditionals: If A happened then B happened, and counterfactual conditionals: If A had happened then B would have happened? Some theorists propose quite different semantics for the two. In contrast, the theory of mental models and its computer implementation interrelates them. It postulates that both can have a priori truth values, and that the semantic bases of both are possibilities: states that are possible for factual conditionals, and that were once possible but that did not happen for counterfactual conditionals. Two experiments supported these relations. Experiment 1 showed that, like factual conditionals, certain counterfactuals are true a priori, and others are false a priori. Experiment 2 replicated this result and showed that participants selected appropriate paraphrases, referring, respectively, to real and to counterfactual possibilities, for the two sorts of conditional. These results are contrary to alternative accounts of conditionals.     

Developmental and sex-related differences in preschoolers' affective decision making

This study investigated developmental and sex-related differences in affective decision making, using a two-deck version of Children's Gambling Task administered to 3- and 4-year-old children. The main findings were that 4-year-old children displayed better decision-making performance than 3-year-olds. This effect was independent of developmental changes in inductive reasoning, language, and working memory. There were also sex differences in decision-making performance, which were apparent only in 3-year-old children and favored girls. Moreover, age predicted awareness of task and the correlation between the latter and decision-making performance was significant, but only in 4-year-old children. This study thus indicates that there is a remarkable developmental leap in affective decision making, whose effects are apparent around the age of 4, which according to our results, also marks the age when the correlation of declarative knowledge and decision-making performance becomes significant.     

Reasoning with deontic and counterfactual conditionals

We report two new phenomena of deontic reasoning: (1) For conditionals with deontic content such as, “If the nurse cleaned up the blood then she must have worn rubber gloves”, reasoners make more modus tollens inferences (from “she did not wear rubber gloves” to “she did not clean up the blood”) compared to conditionals with epistemic content. (2) For conditionals in the subjunctive mood with deontic content, such as, “If the nurse had cleaned up the blood then she must have had to wear rubber gloves”, reasoners make the same frequency of all inferences as they do for conditionals in the indicative mood with deontic content. In this regard, subjunctive deontics are different from subjunctive epistemic conditionals: reasoners interpret subjunctive epistemic conditionals as counterfactual and they make more negative inferences such as modus tollens from them. The experiments show these two phenomena occur for deontic conditionals that contain the modal auxiliary “must” and ones that do not. We discuss the results in terms of the mental representations of deontic conditionals and of counterfactual conditionals.     

Temporal and spatial relations in sentential reasoning

The mental model theory postulates that the meanings of assertions, and knowledge about their context can modulate the logical meaning of sentential connectives, such as "if" and "or". One known effect of modulation is to block the representation of possibilities to which a proposition refers. But, modulation should also add relational information, such as temporal order, to models of possibilities. Three experiments tested this prediction. Experiment 1 showed that individuals spontaneously matched the tense of their conclusions (in Portuguese) to embody implied, but unexpressed, temporal relations in conditional premises. Experiment 2 demonstrated the same phenomenon in inferences from disjunctions. Experiment 3 showed that the number of such implicit relations in inferences from conditionals affects both accuracy and the speed of reasoning. These results support the modulation hypothesis.     

Moderate intensity exercise facilitates working memory

ObjectivesAlthough the effect of exercise on cognitive functioning has received considerable empirical and theoretical attention, the influence of concurrent exercise on complex cognitive function remains poorly understood. Our research was designed to investigate working memory during a bout of dynamic exercise.DesignAn experimental design was used.MethodsIn two experiments, we examined the impact of moderate intensity exercise on performance of a paced auditory serial addition task (Experiment 1, N = 24) and a Sternberg task (Experiment 2, N = 120). The tasks were performed at rest and while cycling at different power outputs.ResultsWe found that moderate intensity exercise increased the number of correct responses at medium-to-fast stimulus presentation rates during the paced auditory serial addition task and lowered the response latency slopes during the Sternberg task.ConclusionsOur findings show that working memory is improved by dynamic exercise at moderate intensities and short duration.     

The modulation of disjunctive assertions

The theory of mental models postulates that disjunctions of the sort, A or B, where A and B are sensible everyday clauses, have a core meaning that allows an inclusive interpretation, referring to three possibilities: A and not-B, not-A and B, and A and B. The meaning of the clauses and knowledge can modulate this meaning by blocking the construction of at least one model of a possibility—for example, “Rui is playing tennis or he is surfing” blocks the model of Rui doing both activities. This theory is implemented in a computer program. Three experiments investigated the core interpretation and interpretations in which the contents of the clauses should block the model of A and B (as in the preceding example), the model of A and not-B, or the model of not-A and B. In Experiment 1, the participants listed the possibilities for each of the four sorts of disjunction. The results corroborated the predicted modulations. In Experiment 2, these predicted interpretations governed the conclusions that participants accepted from disjunctions and categorical premises. In Experiment 3, the predicted interpretations yielded reliable effects on the conclusions that the participants drew for themselves. We relate these results to theories of reasoning.     

Advice conditionals about tips and warnings: interpretations and inferences

Two experiments examine how people interpret and reason about advice conditionals, such as tips, for example, “if you study more your grades will improve”, and warnings, for example, “if you stop exercising you will gain weight”. Experiment 1 showed that when participants reason about whether a tip or warning could be true in different situations, their judgments correspond to a biconditional or conditional interpretation on about half of all trials, but to an enabling or tautology interpretation on many others. Experiment 2 showed that participants make few modus ponens and tollens inferences from tips and warnings, and more modus ponens inferences from tips than warnings. The implications for alternative theories are discussed.