An antidote to illusory inferences

Illusory inferences in conditional expressions

A robber points a gun at a cashier and says: "Only one of these two options is true: If you conceal the combination to the safe, then I kill you; otherwise, if you don´t conceal the combination to the safe, then I kill you." Hearing this statement, most people conclude that, in either case, "I kill you." This is an illusory response, in fact; the valid conclusion states "I don´t kill you." The research reported here studied the roles that different expressions of conditionals ("if-then," "only if," and "if and only if") play in the illusory response. Three experiments show that participants inferred the conclusion "I kill you" from the conditional "if-then" and "I may or may not kill you" from the conditional "only if," while selecting both options with similar frequency for the biconditional "if and only if." These results shed light on the main theories of deductive reasoning.

Overcoming illusory inferences in a probabilistic counterintuitive problem: the role of explicit representations

In the context of conditional probabilities, a good example of the marked discrepancy between intuition and formal reasoning is the Monty Hall dilemma (MHD). We used the MHD to study the effects of practicing the game, making explicit the underlying structure, or enhancing the representation of the different possibilities, on reaching and stating the correct answer. The results of the experiments showed that accumulated experience with the MHD increased the proportion of switching responses but did not change erroneous intuitions (Experiment 1). However, when the dilemma was presented in the form of an adversary game that made the underlying structure more explicit, more participants formed complete mental representations that enabled them to reason correctly (Experiment 2). This result was observed even without any practice with the game if the participants were encouraged to represent possibilities (Experiment 3). Therefore, in this context, correct reasoning seems to depend more on the ability to consider different possibilities than on extensive practice with the game.

Priming in deduction: a spatial arrangement task

The mental model theory assumes that people reason by manipulating mental representations of states of the word, called "mental models." In the present study we used a new deduction task based on diagrammatic premises. We show that a premise can prime other premises that induce similar mental models in a way analogous to the case of words with related meanings, which prime one another. We present three experiments. In Experiment 1 we used an evaluation task. In Experiment 2, a construction task was used. The priming effect was obtained in both cases. In a third experiment we show that the priming effect was still present when partcipants were instructed to ignore a prime displayed before the premises. In all three experiments we compared determinate and indeterminate problems and found faster responses in the former.