Cognitive processing of contradictory statements: an experimental study of reasoning on proverbs in schizophrenia.

Twenty schizophrenic patients and 20 normal subjects matched for age, sex and verbal level were asked to identify, from a list of alternatives, the statement that was the most contradictory to each of 8 proverbs. Schizophrenics (whether severely disturbed or not) were found to be less accurate in detecting the contradictions [F(1,18) = 29.21; p less than 0.0001]. No significant differences between undifferentiated and disorganized DSM-III subtypes were observed. The greatest tolerance of contradictory statements was interpreted in terms of violation of the 'no contradiction principle' and examined in the light of a deficit in logical abilities.