DEDUCTIVE AND INDUCTIVE REASONING IN PARKINSONS-DISEASE PATIENTS AND NORMAL CONTROLS - REVIEW AND EXPERIMENTAL-EVIDENCE

In the present study, fifty-four subjects were tested; twenty-seven wi th idiopathic Parkinson's disease and twenty-seven normal controls mat ched in age, education, verbal ability, level of depression, sex and s ocio-economic status. The subjects were tested on eight tasks. Five of the tasks were the classic deductive reasoning syllogisms, modus pone ns, modus tollendo tollens, affirming the consequent, denying the ante cedent and three-term series problems phrased in a factual context (br ief scripts). Three of the tasks were inductive reasoning, including l ogical inferences, metaphors and similes. All tasks were presented to subjects in a multiple choice format. The results, overall, have shown nonsignificant differences between the two groups in deductive and in ductive reasoning, an ability traditionally associated with frontal lo bes involvement. Of the comparisons performed between subgroups of the patients and normal controls concerning disease duration, disease ons et and predominant involvement of the left and/or right hemisphere, si gnificant differences were found between patients with earlier disease onset and normal controls and between bilaterally affected patients a nd normal controls, demonstrating an additive effect of lateralization to reasoning ability.