Cognitive deficits in schizophrenia can be differentiated into state-linked accompaniments of psychotic episodes and trait-linked signs of a more enduring vulnerability to schizophrenia (Zubin & Spring, 1977; Cromwell & Spaulding, 1978). Elsewhere (Spring & Zubin, 1978) we suggested that a marker of psychotic episodes is one that deviates in highly symptomatic schizophrenic patients and normalises as their florid psychotic symptoms remit. A stable vulnerability marker, in contrast, continues to deviate in remitted patients, their biological relatives, and others who are vulnerable to schizophrenia but not floridly psychotic. In addition, Nuechterlein & Dawson (1984) proposed a mediating vulnerability marker which demonstrates characteristics of both vulnerability and episode markers. On such a marker, asymptomatic vulnerable individuals differ from normal; the advent of psychosis magnifies the deviation.