Inference Complexity and the Logic Bias Effect in Conditional Reasoning

The hybrid dual processing model maintains that humans possess an extensive intuitive logic featuring multiple deductive inference forms. One basis for this claim is the presence of a logic bias effect on the dual instructional set paradigm. Implicit logical processing interferes with efforts to respond on the basis of belief to a greater extent than belief-based processing interferes with efforts to respond on the basis of logical validity. An important question for the hybrid model is whether there are limits to intuitive logic. Across two experiments, we manipulated inference complexity (defined by inference direction and the presence or absence of negation) on a conditional reasoning task by crossing conditional inference type (modus ponens: MP, modus tollens: MT) and conclusion wording (normal, contrary). We found that the presence or absence of the logic bias effect depended on the complexity of processing required by the inference. In particular, the extent to which logical processing interfered with efforts to respond according to belief was a function of inference complexity. We also provide evidence that the logic bias effect is positively related to analytical thinking disposition and negatively related to working memory capacity. These results suggest that there are limitations to intuitive logic even within everyday inferences.