What determines continuous performance task performance?

The Continuous Performance Task (CPT) is widely used as an indicator of cognitive dysfunction in schizophrenia. It is still unclear, however, exactly what this test measures. We examined the contribution of motor speed, reaction time measures, mental effort, and level of psychopathology to the performance on a double-stimulus CPT. This study included schizophrenia patient groups, depressive patient groups, and patient and normal control groups. Subjects were retested twice: once after 1 week and again at 3 months. In patients with schizophrenia or depression, the sensitivity measure (d') was strongly and consistently associated with motor speed and with the standard deviation of reaction times (response variability) to target stimuli. The association with response variability was also found at followup tests in the control groups. We conclude that in patients with schizophrenia or depression, the sensitivity measure of a double-stimulus CPT is associated with cognitive mechanisms that determine motor proficiency and response variability.