Finding Evidence of Deductive and Abductive Reasoning Abilities: An Experiment with Lateral-Brain-Damage Patients

In narrative discourse, explanation can be considered abductive reasoning, described as a creative type of reasoning which generates new ideas, and prediction can be considered logical deductive reasoning. Given the well-known associations with hemisphere processing and reasoning associations, it would be expected that patients with left hemisphere brain damage would exhibit more evidence of explanation versus prediction in reasoning and patients with right hemisphere brain damage would exhibit more evidence of prediction versus explanation in reasoning. By observing actual linguistic evidence of reasoning in left and right hemisphere brain damaged patients in comparison to that of a control group, we were able to discover important differences between these groups. Contrary to assumed wisdom, patients with left hemisphere damage produced more utterances of prediction than of explanation and patients with right hemisphere damage produced more utterances of explanation than prediction on a narrative discourse task. Linguistic processing and cognitive processing are discussed as explanations for these results.