Differential Diagnosis of Schizophrenic and Nonschizophrenic Adolescents by Tests Based on Interference Theory*

Interference theory is proposed as one of the better current constructs that may explain schizophrenic deficits. A battery of psychological tests that embody competing stimuli was created. Consecutive adolescent patients admitted to a general hospital psychiatric inpatient service were tested. The patients were diagnosed as schizophrenic or nonschizophrenic, based on classical symptomatology. Both groups were comparable in terms of age, years of schooling, and medications given. The results showed that although all group mean differences were in the predicted direction, only one measure, the Competing Voices Task, significantly differentiated between the two groups. A discriminant function and classification analysis showed that a function could be derived which correctly classified 8 of the 9 subjects in the nonschizophrenic group, and 9 out of the 12 in the schizophrenic group, solely on the basis of their scores on two of the measures. Adding the other variables did not increase the discriminating ability of the test battery as a whole. A general hypothesis was proposed relating to sufficient conditions for the evocation of a schizophrenic deficit, and the difficulties of applying current theories were underlined.