IMMEDIATE VERSUS DELAYED VISUAL MEMORY TASK-PERFORMANCE AMONG SCHIZOPHRENIC-PATIENTS AND NORMAL CONTROL SUBJECTS

In an exploratory study, 10 schizophrenic patients and 10 normal contr ol subjects performed immediate and delayed memory tasks, which were v ariants of previously developed continuous performance tests. Both tas ks required participants to identify five-digit numbers which were rep eated. Numbers were presented in series for 500 ms each and separated by a 500-ms time-out period. In the immediate memory task, subjects we re to respond if a number was identical to the one that had immediatel y preceded it. The delayed memory task differed from the first task in that a longer delay (3.5 s) between stimuli was introduced, and durin g this delay distracter stimuli appeared. While normal control subject s performed accurately on both tasks (exceeding 80% correct detections ), schizophrenic patients performed poorly, performing worse on the de layed memory task than on the immediate memory task. Rates of commissi on errors (responses made to similar, but not identical numbers) were nearly equal between groups on the immediate memory task, but on the d elayed memory task normal control subjects made relatively more commis sion errors while schizophrenic patients made fewer commission errors. No differences in response latencies were observed between subject gr oups or tasks. This paradigm may prove useful in discriminating subtle differences in immediate and delayed memory capability among psychiat ric populations and normal control subjects. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.