[Short-term memory functioning in schizophrenics--late components (P3) of the event-related potential recorded from...

Event-related potentials were measured in 14 schizophrenic patients and age-matched 14 normal control subjects during a Sternberg's memory-scanning paradigm. The stimuli used were digits presented visually. In this paradigm each set of stimuli was presented for memorization (memory set), while varying the number of items (1, 2, 4) in each set, and following the mask stimulus, a probe item (test stimulus) appeared and was identified by the subject as belonging or not belonging to the memory set. Reaction times (RT) and performance accuracy were computed and ERPs to the test stimuli were recorded for each memory set size and response type. As P3 peaks in some schizophrenic patients were rather ambiguous, instead of using the conventional peak-picking method, P3 latency was determined from single trials using an adaptive correlating filter (ACF) technique, and P3 amplitude was measured from the latency-adjusted averages to reduce the jittering effect. For the behavioral measures, significant difference was not obtained between the groups. Though P3 latency increased and amplitude decreased as a function of memory set size for the normal controls, by contrast, neither latency nor amplitude of P3 was not influenced by memory set size for schizophrenics. Moreover, schizophrenic patients had smaller single trial P3 latency/RT correlations compared to normal controls. Applying the two memory-load dependent processes by Lewine, which are memory strength-evaluation and serial search stage, impaired ability of rehearsing or allocating attentional resource to each item, producing an increase in the strengths of their representations in the working memory, was suggested for schizophrenics. Accordingly, serial search process was hardly undertaken by schizophrenics, at least before response determination.