A method and apparatus for diagnosing schizophrenia, schizophrenia disorder subgroup, or predisposition thereto in a test subject is disclosed. The method includes the steps of determining an interhemispheric switch rate of the test subject. In one embodiment, the interhemispheric switch rate of the test subject is under conditions of increasing rate of dichoptic reversal, and comparing the switch rate with a corresponding reference switch rate to diagnose presence or absence of schizophrenia, a schizophrenic disorder subgroup, or predisposition thereto. In a preferred embodiment, the interhemispheric switch rate is determined by measuring the rate of binocular rivalry in the test subject. Also disclosed is use of a diagnostic method in genetic linkage studies for the identification of the molecular defect(s) underlying schizophrenia, and for the identification of compounds which may alleviate the disorder.