Deficits in initial feature registration of schizophrenics and substance abusers

Information processing deficits are consistently reported for schizophrenics. The present study evaluated if the longer duration required by schizophrenics to visually recognize a target may qualify, as proposed by previous studies, as a vulnerability and/or trait biological marker. Critical stimulus duration (CSD) was used as the index of initial target registration and recognition. The CSD is the minimal duration, in ms, to meet task criterion, which in the present study was seven consecutive identifications of the target letter 'T' or 'A'. There were 13 normal controls, 11 methadone maintenance experimental controls, 21 chronic schizophrenics and 12 subacute schizophrenics. Analysis of variance revealed that the CSDs of normal controls and subacute schizophrenics were not statistically different (p > 0.05); the CSDs of chronic schizophrenics were not statistically different from methadone controls (p > 0.05), while the chronic schizophrenics and the methadone controls' CSDs were statistically different from the normal controls and the subacute schizophrenics. The results support earlier reports of long target duration required by chronic schizophrenics for feature recognition. Since retarded CSDs were obtained for methadone control but not for acute schizophrenics, the CSD does not qualify as a specificity or a vulnerability index for schizophrenia. A neurophysiological explanation is proposed for the findings.