1. A method for diagnosing schizophrenia, schizophrenic disorder subtype, or predisposition thereto in a test subject, said method including the steps of: (a) measuring an interhemispheric switch rate of the test subject; and (b) comparing the measured switch rate with a corresponding reference switch rate to diagnose presence or absence of schizophrenia, schizophrenia disorder subtype or predisposition thereto.