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The Roots of Deductive Reasoning: Neuroimaging and Behavioral Investigations


Deductive reasoning has been an object of investigation in psychology for almost a century now. Yet, key questions remain unanswered. These include (but are not limited to) the relationship between deductive reasoning and other psychological processes (such as language and memory), the identity of the neurological structures that are core to the deductive process, the source of the hierarchical structures on which deduction depends, whether deduction is a modular or domain general process, and what the source is of the facilitation that is frequently observed when deductive problems are framed in different ways. In order to address these questions, this thesis will present three experiments that shed light on different aspects of deduction. Study 1 is an fMRI study which replicates prior findings regarding the relationship between language and deduction and reveals a new dissociation between deduction and working memory. Study 2, a neuromodulation study, is a logical extension of the findings regarding deduction and language from Study 1 and other prior studies. Here, a form of transcranial magnetic stimulation (TMS) is used to manipulate brain function in order to establish a causal dissociation between brain areas that support language and those believed to support deduction, specifically with regard to the hierarchical frameworks on which both language and deduction depend. Finally, in Study 3, a large online study is used to test the Social Exchange Theory of facilitated performance on the Wason Card selection Task on a more diverse sample than has been the case in the past, especially with regard to the cues that have been suggested to trigger the underlying cognitive “modules.” This study also tests the relationship between facilitation on the Wason Task and a number of individual differences, revealing novel associations with personality traits and with psychopathology. Together, these three studies provide a clearer picture of how deductive reasoning, one of our most distinctively human capacities, is situated amongst our other cognitive abilities.

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