Filling the preparatory interval with temporal information or visual noise: crossover effect in schizophrenics and controls

Three variants of a simple reaction time task with regular and irregular series of different preparatory intervals (PIs) were presented to schizophrenics and a control group of alcoholics and normals: the visual warning signal (WS) either (1) remained fixed, (2) shrank at a constant rate, or (3) changed in size erratically. Time information provided by shrinking WSs reduced the average reaction time in all groups and attenuated the crossover effect (COE) of schizophrenics, although even here more schizophrenics than controls had COE-scores greater than or equal to 25 msec. Erratically changing WSs introduced the COE in controls. Within groups the COE was not related to general response speed, age, duration of hospitalization, or medication. Results are interpreted as indicating that schizophrenics eschew controlled anticipatory processes on the basis of WS- and PI-information which are crucial for motor preparation when PIs are too long to allow an automatic perceptual grouping of warning and imperative stimulus. This may also occur in controls when time estimation is impeded by distraction.