Mental models and human reasoning

Abstract

To be rational is to be able to reason. Thirty years ago psychologists believed that human reasoning depended on formal rules of inference akin to those of a logical calculus. This hypothesis ran into difficulties, which led to an alternative view: reasoning depends on envisaging the possibilities consistent with the starting point--a perception of the world, a set of assertions, a memory, or some mixture of them. We construct mental models of each distinct possibility and derive a conclusion from them. The theory predicts systematic errors in our reasoning, and the evidence corroborates this prediction. Yet, our ability to use counterexamples to refute invalid inferences provides a foundation for rationality. On this account, reasoning is a simulation of the world fleshed out with our knowledge, not a formal rearrangement of the logical skeletons of sentences.

Fig. 1.

Reasoning about relations that are easy to visualize but hard to envisage spatially activated areas in the secondary visual cortex, V2 (43). The figure shows the significant activation from the contrast between such problems and abstract problems (in terms of the color scale of z values of the normal distribution) with the crosshairs at the local peak voxel. Upper Left: Sagittal section, showing the rear of the brain to the left. Lower Left: Horizontal section, showing the rear of the brain to the left. Upper Right: Coronal section, with the right of the brain to the right. [Reproduced with permission from ref. (Copyright 2003, MIT Press Journals).]

Fig. 2.

Interaction between the type of problem and level of difficulty in right frontal pole, Brodmann's area 10 (81). After the 8-s window of the presentation of the problems (shown in gray, allowing for the hemodynamic lag), the inferences that called for a search for counterexamples activated this region more than the easy inferences did. There was no difference in activation between the hard and easy mathematical problems, and only the counterexample inferences showed activity above baseline. [Reproduced with permission from ref. (Copyright 2008, Elsevier).]