There is a large body of research that has established change in reaction time as one of the major psychological performance deficits in schizophrenia (Shakow, 1963). In addition to consistent differences between patients and normals, relationships have been reported (Rosenthal, Lawlor, Zahn and Shakow, 1960) between general severity of illness and reaction time within a group of chronic schizophrenics. More recently, Zahn and Rosenthal (1963) have shown that acute schizophrenics also perform deficiently in reaction time; they hold an intermediate position between normal subjects and chronic schizophrenic patients. Shakow (1963) reports that in some of the earlier work with chronic patients “paranoids” tended to show little, if any, reaction time deficit, but that it was the hebephrenic patients who performed poorly. Thus it seems unlikely that reaction time is a general measure of deficit in schizophrenia, since available evidence shows it to be related to chronicity (in terms of duration of illness), general severity of illness, and schizophrenic subtype. The deficit reflected in reaction time has been characterized by Shakow (1963) in terms of associative interference. That is, the schizophrenic is distracted by “irrelevant aspects of the stimulus surroundings—inner and outer—which prevent his focusing on the ‘to-be-responded-to’ stimulus”.