Neural correlates of acoustic reasoning.

We report an fMRI experiment on deductive reasoning with acoustically presented problems. Twelve volunteers received problems in which an acoustic stimulus came from the left or the right of another stimulus. The participants then heard a third stimulus coming from the left or the right of one of the proceeding stimuli. Their task was to determine the spatial relation between the two stimuli they never perceived together. In the psychology of reasoning, such problems are called transitive inferences or three-term-series problems. During the early phases of the inference, activity in primary and secondary acoustic areas and in the anterior prefrontal cortex was found. Further processing was accompanied by activity in medial frontal gyrus, the cingulate cortex, and in the parietal cortex. In the final phase, activity was found in the left frontal cortex, the right cerebellum, the right superior temporal gyrus, and in the parietal lobule. These results show that different brain areas are related to different phases of an inference. Based on these findings, we propose a three-stage-model of acoustic reasoning and identify the neural structures that are involved in the cognitive processes taking place in each phase. The results also show how acoustically presented reasoning problems differ from problems in which the problems are presented visually.