The British Journal of Psychiatry 128: 456-461 (1976)
© 1976 The Royal College of Psychiatrists

'Filtering' and the cognitive deficit in schizophrenia

DR Hemsley and SL Zawada

This study attempted to clarify the nature of dysfunction in the selective attention of schizophrenics. Within the framework of Broadbent's (1971) theory of information processing it was argued that 'filtering' inefficiency should be reflected in a reduction in the discrepancy in performance on a short-term memory task between the condition of pre-instruction as to the relevant material and that of post-instruction. Three groups of subjects, 10 schizophrenics, 10 depressives, and 10 normals, matched for age and intelligence were tested on such a task. While the overall performance of normal subjects was superior to that of both psychiatric groups, depressives and schizophrenics did not differ. The normal group also showed a significantly greater improvement with pre-instruction than the psychiatric groups; again, the schizophrenics and depressives did not differ significantly, though there was a tendency for schizophrenics to benefit less than depressives from pre-instruction. It appears that 'filtering' difficulties as here defined may not be specific to schizophrenia. Alternative conceptualizations of the cognitive abnormalities shown by schizophrenics, such as slowness of information processing and difficulties in response selection, may be more useful.