Deficits of problem-solving ability in focal brain-damaged patients, with special reference to frontal lobe dysfunction, were investigated by two neuropsychological tests: Temporal rule induction test and Hypothesis-testing measure. Subjects consisted of 84 chronic brain-damaged patients (31 with anterior cerebral lesions and 53 with posterior lesions). The study's aim was to investigate the effects of frontal lobe damage on two aspects of inductive reasoning, prediction and hypothesis behavior. When prediction was examined by Temporal rule induction test, patients with anterior lesions showed deficits in predicting a rule, even in the memory-aid condition in which memory factors were excluded. The poor results on Temporal rule induction test in frontal patients did not appear to be related to deficits in temporal integration, which is generally interpreted as frontal dysfunction. Rule induction may be impaired by frontal damage whenever complicated information-processing is required, even when temporal succession is not involved. Second, two stages of hypothesis behavior, hypothesis-formation and hypothesis-testing, were evaluated. Patients with anterior lesions showed impairment in hypothesis-formation. Their decreased fluency in hypothesis production affected the hypothesis-testing process. However, frontal patients committed fewer errors, most of which were perseverative (lose-stay errors) on hypothesis-testing. Patients with posterior lesions revealed other characteristic errors, such as inconsistent responses and divergent-type errors (improper lose-shift errors). The hemispheric site of the lesion affected only the ability to maintain a hypothesis (win-shift errors). The results illustrated the differences in problem-solving deficits in these two groups of patients. Disturbed prediction of future events, decreased hypothesis fluency, and abnormal lose-stay behavior in patients with frontal lobe damage may be crucial factors in coping with daily problem-solving situations.
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