Global capacity reduction and schizophrenia

Abstract

This paper reviews the evidence for a specific deficit in the flow of information through the schizophrenic processing system. It is suggested that there is little to support the notion of a single defective mechanism underlying schizophrenic cognitive dysfunction. The lack of a valid and reliable metric for measuring degree of difficulty across tasks and a lack of concern with matching tasks for attentional processing load, detracts from the usefulness of available results. The applicability of a global limited capacity model of selective attention to schizophrenic information processing is discussed as the most appropriate means of systematizing the wealth of published empirical data.

A neurologist looks at “schizophasia”

“…In contrast to our previous results, distraction interfered with the subjects' ability to shadow the relevant message, but it did not affect their subsequent recall of its content. Although the comparison of results across studies is complicated by a number of factors, the general pattern of results is perhaps most consistent with a suggestion made by Knight and Russell (1978), who argued that schizophrenics may suffer from a general reduction in the global capacity to process information. According to their argument, the specific manifestations of this global deficiency will vary as a function of task demands.…”

Cognitive Functioning in Schizophrenia: Implications for Psychiatric Rehabilitation

“…In Factor 3, there appears to be such a trade-off between nonverbal memory and concept manipulation performance, evidenced by the negative factor loading of the nonverbal memory measure. Such a trade-off could be the result of reallocating limited processing capacity from one functional domain to another (Knight and Russell 1978; Gjerde 1983). In that sense, cognitive recovery may in part represent more efficient allocation of cognitive capacity in response to environmental demands.…”

Visual information-processing deficits in chronic schizophrenic subjects using tasks matched for discriminating power.

“…Results from these studies have shown that distraction reduces the number of items that schizophrenic persons can recall, relative to their recall in a matched neutral condition, and are a clear demonstration of a specific vulnerability in the schizo-phrenic processing system. As such, these data represent a challenge to recent views that schizophrenic deficits are the product of a global reduction in attentional capacity (Gjerde, 1983;Knight & Russell, 1978). To reconcile these results with a generalized capacity-reduction account of cognition in schizophrenia, Gjerde (1983) has drawn a distinction between psychometric considerations such as discriminatory power, on the one hand, and amount of processing effort (Hasher & Zacks, 1979;Kahneman, 1973), on the other, and has concluded that those studies that have controlled for task difficulty level "have reported that schizophrenic dysfunction is most manifest when effortful processing is required" (p. 63).…”

“…Although it has not been difficult to design tasks that uncover cognitive dysfunctions in schizophrenic patients, demonstrating the specificity of such deficits to particular tasks or subgroups of patients has proved more frustrating (Knight & Russell, 1978). A methodological issue that undermined much of the work comparing the performance of schizophrenic patients on different tasks was first identified by Chapman and Chapman (1973).…”