| Individuals with severe psychopathology show deficits on a variety of tasks, although the diagnostic and cognitive specificity of these deficits is largely undetermined. Schizophrenics have inconsistently shown auditory sensory memory deficits, measured via mismatch negativity (MMN) in the event-related potential (ERP), but have consistently shown working memory deficits, measured behaviorally and with ERPs. A number of questions can be raised about the appropriateness of the MMN paradigms used to date in schizophrenics. These confounds may account for the inconsistent results in the literature. Depressives' memory deficits have been conceptualized more abstractly, in terms of controlled processing involved in working memory. Sensory memory has not been examined in depressives, although theories predict that it is intact.;An ERP study of sensory and working memory was designed to avoid confounding MMN with other components. Schizophrenics, depressives, and controls performed a tone discrimination task, in which subjects counted or ignored tones. Evidence of memory abnormalities emerged as a function of diagnosis and stimulus sequence. All three groups showed intact auditory sensory memory, with comparable amplitudes and sequence effects. Schizophrenics did not differ from controls overall, but, in analyses as a function of diagnostic subtype, MMN was reduced in paranoid schizophrenics. Depressives showed dysfunctional working memory, as indexed by exaggerated N2b. Schizophrenics did not differ from controls overall, but, in analyses as a function of diagnostic subtype, N2b for was nonsignificantly higher in negative-symptom schizophrenics, who most resemble depressives. Results suggest that in certain MMN paradigms which removed stimulus confounds, schizophrenics can produce an normal MMN, which is appropriately influenced by preceding stimulus sequence. In addition, results suggest abnormal voluntary, strategy-sensitive processing in psychopathology, particularly in patients showing negative symptoms. |
