The effect of social content on deductive reasoning: an fMRI study

Abstract

Psychological studies of deductive reasoning have shown that subjects' performance is affected significantly by the content of the presented stimuli. Specifically, subjects find it easier to reason about contexts and situations with a social content. In the present study, the effect of content on brain activation was investigated with functional magnetic resonance imaging (fMRI) while subjects were solving two versions of the Wason selection task, which previous behavioral studies have shown to elicit a significant content effect. One version described an arbitrary relation between two actions (Descriptive: "If someone does ..., then he does ..."), whereas the other described an exchange of goods between two persons (Social-Exchange: "If you give me ..., then I give you ..."). Random-effect statistical analyses showed that compared to baseline, both tasks activated frontal medial cortex and left dorsolateral frontal and parietal regions, confirming the major role of the left hemisphere in deductive reasoning. In addition, although the two reasoning conditions were identical in logical form, the social-exchange task was also associated with right frontal and parietal activations, mirroring the left-sided activations common to both reasoning tasks. These results suggest that the recruitment of the right hemisphere is dependent on the content of the stimuli presented.

Figure 1

Examples of the stimuli presented in the SE (top), DES (middle), and baseline (bottom) tasks (translated from Italian). The first two tasks differ only in propositional content, whereas their logical structures are identical. In the baseline task, subjects have to indicate all and only the cards that mention the objects whose names are shown in the conditional sentence.

Figure 2

From top to bottom, activation foci for the DES and the SE tasks (P < 0.001, uncorrected for multiple comparisons; t > 4.14), for the conjunction analysis (P < 0.01, corrected for multiple comparisons; t > 4.02), and for the direct comparisons between the two tasks (red, SE > DES; blue, DES > SE; P < 0.005, uncorrected for multiple comparisons; t > 3.17). Areas of increased activation were superimposed on seven representative axial slices of the group mean anatomic image, derived from the T1‐weighted images of the participants. The number above each slice represents its distance (in mm) from the AC–PC plane. The height of the individual slices is also shown, in the rightmost part of the figure, on a rendering of the same average brain.

Figure 3

In the center of the figure, lateral views of renderings derived from the subjects' individual normalized T1 images are shown, with superimposed clusters of activation in DES (top) and SE (bottom) reasoning tasks. The colored arrows link the right‐hemispheric frontal and parietal clusters activated in the SE task with histograms indicating BOLD signal change percentage (amplitude of the hemodynamic response curve) in both reasoning tasks (blue, DES; red, SE), after baseline subtraction. For each effect, standard error bars are indicated. Asterisks above histogram bars indicate a significant effect. MNI stereotactic coordinates of the maxima of the clusters (as reported in Table I) are shown in the superior part of each graph.