Cognitive functioning in schizophrenia. I. Stimulus analysing and response selection processes

Effectiveness of Cognitive Rehabilitation for Improving Attention in Patients with Schizophrenia

Many patients with chronic schizophrenia who are treated in traditional occupational therapy programs demonstrate lower level deficits involving cognition and, more specifically, attention. This study examines the applicability of the cognitive rehabilitation treatment modality to patients with schizophrenia as compared with the traditional one-to-one task-oriented approach. Results indicated no significant difference between the two treatment methods. Overall, the subjects from both groups did show improvement in scores on the shell sort task of the Bay Area Functional Performance Evaluation (BaFPE). Scores for self-confidence, motivation, and efficiency improved for the subjects in both groups in at least four of the five task scores of the BaFPE. Significant improvements also were noted in five psychological tests of attention and memory for both groups. This study supported the importance of hierarchically arranged crafts and cognitive rehabilitation in an environment with reduced sensory input. Treatments that were structured, concrete, and visual were most effective.

The speed of visual attention in schizophrenia: electrophysiological and behavioral evidence

Schizophrenia is characterized by a substantial slowing of manual response times and by impairments in attention. However, prior research has not investigated whether attention itself is slowed in schizophrenia, and this was the goal of the present study. In Experiment 1, the N2pc component of the event-related potential waveform-an electrophysiological correlate of the focusing of attention-was recorded from 24 schizophrenia spectrum patients and 13 control subjects. Although behavioral response times were delayed by over 100 ms in the patient group, the onset latency of the N2pc component was virtually identical across groups, and no reduction in N2pc amplitude was observed in the patient group. In Experiment 2, a new cueing paradigm was developed to provide a behavioral measure of the speed of attention in 22 schizophrenia spectrum patients and 13 control subjects. We found that the average time required to allocate attention to a cued location was only 19 ms greater for the patient group than for the control group, with most patients within the range of the control subjects. Together, these experiments revealed little or no slowing of the allocation of visual-spatial attention in patients with schizophrenia. Thus, the mechanisms responsible for allocating attention to salient visual targets appear to be largely unaffected by the illness, and the well documented slowing of manual response times in schizophrenia cannot easily be explained by a slowing of attention.

Impairment of willed actions and use of advance information for movement preparation in schizophrenia

OBJECTIVES

To assess willed actions in patients with schizophrenia using reaction time (RT) tasks that differ in the degree to which they involve volitionally controlled versus stimulus driven responses.

METHODS

Ten patients diagnosed with schizophrenia and 13 normal controls of comparable age were tested. Subjects performed a visual simple RT (SRT), an uncued four choice reaction time (CRT), and a fully cued four choice RT task. A stimulus 1(S1)-stimulus 2(S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 (no warning signal or precue) 200, 800, 1600, or 3200 ms.

RESULTS

The patients with schizophrenia had significantly slower RTs and movement times than normal subjects across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, fully cued CRTs were significantly faster than the uncued CRTs. However, the S1-S2 interval had a differential effect on CRTs in the two groups. For the normal subjects fully cued CRTs and SRTs were equivalent when S1-S2 intervals were 800 ms or longer. A similar pattern of effects was not seen in the patients with schizophrenia, for whom the fully cued CRT were unexpectedly equivalent to SRT for the 200 ms interval and expectedly for the 1600 ms S1-S2 interval, but not the 3200 or 800 ms intervals.

CONCLUSIONS

Patients with schizophrenia were able to use advance information inherent in SRT or provided by the precue in fully cued CRT to speed up RT relative to uncued CRT. However, in the latter task, in which the volitional demands of preprogramming are higher since a different response has to be prepared on each trial, patients showed some unusual and inconsistent interval effects suggesting instability of attentional set. It is possible that future studies using RT tasks with higher volitional demands in patients with predominance of negative signs may disclose greater deficits in willed action in schizophrenia.

Abnormalities of response processing in a chronic psychiatric group. A possible predictor of failure in rehabilitation programmes?

This study attempted to identify, in a mixed group of chronic patients, a specific measure of cognitive processing that may be of use in predicting dependence on psychiatric care. The measures investigated are derived from reaction-time tasks. Difficulties of response processing seem to account for the largest amount of variance in current service use. When compared with other variables shown to have some predictive power (e.g. social behaviour, symptoms and chronicity), the reaction time measures fare well. Functions derived from discriminant analyses using all the variables correctly classified 90% of those requiring day care and 95% of those requiring night care. Stepwise methods produced lower classification rates but always included reaction-time measures in the predictor set. Patients with continuing cognitive difficulties are likely to remain in more supportive psychiatric settings despite rigorous rehabilitation procedures.

A mechanism to inhibit input activation and its dysfunction in schizophrenia

Schizophrenics appear to be unable to regulate adequately the effects of external stimulation, but the cause of this deficit is unclear. Recent evidence suggests that input activation can normally be inhibited by an appropriate leading or conditioning stimulus; such inhibition has been found to be diminished in schizophrenics. Based on this evidence, a feed-forward regulating mechanism that serves to stabilise reactivity to environmental events is described; it is hypothesised that failure of the mechanism to inhibit adequately surges of activity is an underlying cause of schizophrenic symptoms. Some ways to test the validity of the mechanism are proposed, and an outline presented of steps to link the mechanism's dysfunction to schizophrenia.

Relationship between subjective self-report of cognitive dysfunction and objective information-processing performance in a group of hospitalized schizophrenic patients

This study examines the relationships between subjective self-report of cognitive difficulties associated with schizophrenia and performance parameters of an objective choice reaction time task. The predicted relationships did not emerge and the results are discussed with regard to the methodological difficulties of measuring self-report and the features of the CRT task used. One positive finding was the significant relationship between chronicity of illness and the CRT measures.

Decisional processing in paranoid and non-paranoid schizophrenics

40 schizophrenic subjects, divided into paranoid/non-paranoid categories and 14 normal controls were presented a task which involved making "same-different" judgments during random presentations of a series of visual comparison stimuli with a standard which represented the midpoint of the stimulus continuum. Using Sternberg's Choice RT paradigm for studying the locus of cognitive deficit, difficulty at the response-selection stage was manipulated while holding other stages constant. It was predicted that paranoids would have shorter RTs at easy decision points and longer RTs at difficult decision points relative to non-paranoids. The directions of the differences were as predicted but did not attain statistical significance. Both schizophrenic groups, compared to normals, made significantly fewer "same" responses on those trials where the comparison and standard were most similar.

Frontal lobe dysfunctions in schizophrenia--II. Impairments of psychological and brain functions

In Part I of this paper (Levin, 1984), it was proposed that the phenomena of eye movement impairments in schizophrenia are consistent with a dysfunction of frontal eye field mechanisms of ocular-motor control. In Part II, a frontal lobe dysfunction in schizophrenia is also proposed on the basis of clinical, psychological, neurochemical, and neuropathological grounds. There are striking similarities between the clinical frontal syndrome and negative symptom schizophrenia. Parallels between experimental studies of disturbances in attention and information processing, in humans and animals with frontal lobe lesions on the one hand, and in schizophrenics on the other, are noteworthy. The evidence for seemingly disparate dysfunctions in schizophrenia of eye movements, psychomotility, cognition, arousal, motivation and affect, is consistent with a disruption of frontal lobe mechanisms of stimulus-response and drive-response modulation. Studies on the neurochemistry and neuroanatomy of schizophrenia provide further evidence for a frontal lobe dysfunction in a subgroup of schizophrenic patients, particularly those with negative symptoms.

Abolition of the expression but not the acquisition of latent inhibition by chronic amphetamine in rats

The animal amphetamine model of schizophrenia has been based primarily on stereotyped behavior. The present study sought to demonstrate an amphetamine-induced deficit in attentional processes. To this end, the effects of acute and chronic (14 days) 1.5 mg/kg dl-amphetamine administration on the ability of rats to ignore irrelevant stimuli were examined using the paradigm of latent inhibition (LI) in a conditioned emotional response (CER) procedure. The procedure consisted of three stages: pre-exposure, in which the to-be-conditioned stimulus, tone, was presented without being followed by reinforcement; acquisition, in which the pre-exposed tone was paired with shock; and test, in which LI was indexed by animals' suppression of licking during tone presentation. Experiment 1 showed that chronic but not acute treatment abolished LI. Experiment 2 showed that animals receiving chronic amphetamine pretreatment but pre-exposed and conditioned without the drug, exhibited normal LI. In Experiment 3, animals which received chronic amphetamine pretreatment and were pre-exposed under the drug but conditioned without it, also showed normal LI. The implications of these results for the animal amphetamine model of schizophrenia are discussed.

Selective language deterioration in chronic schizophrenia

Chronic schizophrenics as a group were inferior to controls on tests of neuropsychological function. When divided into groups according to length of illness they differed from each other primarily in tests of language. No other deficits in cognitive function progressed; the performance of the patients on memory, visuo-spatial tasks, rate of information processing and abstract thinking did not decline according to length of illness. The results indicate that chronic schizophrenia is characterised by a selective deterioration of language, which correlates with the notion that schizophrenia may be associated with left hemisphere dysfunction.

Memory in functional psychosis

Acute schizophrenic, chronic schizophrenic, and depressive patients (20 of each) were compared with normal subjects and six groups of patients with organic brain disease. They were given tests of verbal learning (left hemisphere type function) and pattern recognition memory (right hemisphere type function). All functional psychotics showed impaired memory. Acute schizophrenics were, however, only impaired on the verbal task, suggesting left hemisphere dysfunction, while chronic schizophrenics and depressives were impaired on both tasks, suggesting bilateral dysfunction.

Consciousness, information processing and schizophrenia

The symptoms of schizophrenia can be interpreted as the result of a defect in the mechanism that controls and limits the contents of consciousness. This defect can be understood as excessive self-awareness. Normally most of the complex information processing which is continuously required by even simple acts of perception, language and thought goes on below the level of awareness; whereas in schizophrenic patients some of this processing, or the results of this processing, not in themselves abnormal, become conscious. This excessive awareness can account for the typical symptoms of schizophrenia and explains many of the specific cognitive abnormalities found in schizophrenic patients.

The nature of deficit among paranoid and nonparanoid schizophrenics in the interpretation of sentences: an information processing approach

Compared paranoid and nonparanoid schizophrenics to normal controls on a sentence verification task. The task permitted separation of times taken for central scanning and comparison operations and for operations associated with response selection and response execution. Neither group of schizophrenics took more time than normal controls for the latter operations; however, both groups of schizophrenics took longer at central scanning and comparison. Performance on this task was compared to previous results in which schizophrenics were similar to normals on times for central scanning and comparison, but took longer for non-central aspects of processing. It was condluded that the present deficit at the central processing level was attributable to deficient short-term memory of the encoded version of the sentence during the scanning and comparison operations. The absence of differences in the time taken for the non-central operations was ascribed to the exclusion of sentence encoding from the present latency times.

Similarities and differences in encoding processes in chronic schizophrenics and normals

The encoding of visual stimuli was compared for 9 female chronic nonparanoid schizophrenics and 9 normals using the Sternberg paradigm. This paradigm allows an examination of several hypothetical stages in information processing using a reaction time measurement. Degradation level (degraded vs nondegraded), type faces of letter stimuli (varied versus constant type face), and order of degradation levels (mixed or constant level across a block of trials) were manipulated in order to examine differences in encoding process between the two groups. Results suggest two subprocesses in encoding, only one of which is defient in schizophrenics. Additional processing of encoded information at a memory stage may be comparable in normal schiziphrenics. Chronic schizophrenics are also more easily disrupted by the context of varying stimulus conditions such as mixing degradation levels and type faces. This finding suggests schizophrenic perseveration in encoding processes.

The effect of varying the rate of presentation on the information transmission of schizophrenic and control groups

Groups of subjects were tested on a paced serial reaction-time task in order to study the effect of varying the rate at which information was presented. The groups were: two groups of patients with acute schizophrenia but differentiated on the basis of primary symptoms, a group of institutionalized schizophrenic patients, a group of neurotic patients and a normal group. All groups showed a reduction in efficiency when the presentation rate was increased. The groups most adversely affected were the non-integrated and institutionalized schizophrenic patients. The integrated schizophrenic and the neurotic groups were affected to a lesser degree, the normal groups being least affected. These results favour a dimensional view of personal illness, in which deficits are most marked in patients with non-integrated schizophrenia.

Response-selection processes in paranoid and nonparanoid schizophrenia

Previous research (Marshall, 1973) has shown that the most pronounced component of deficit on a choice reaction time task among a mixed schizophrenic sample involved response-selection processes. Other evidence has indicated that paranoids may be more deficient in this respect than nonparanoids. Hence, it was hypothesized that the former subgroup of schizophrenics would display response-selection deficit while the latter subgroup would display either less or no deficit. Response-selection processes were re-examined using the CRT paradigm with comparisons carried out among paranoid and nonparanoid schizophrenics and a group of nonschizophrenic controls. Results indicated that only the paranoid schizophrenics displayed abnormally retarded response-selection operations, the nonparanoid schizophrenics being nonsignificantly discriminable from the controls. It was suggested that past evidence of CRT response-selection deficit among mixed schizophrenics might have been attributable primarily to the performance of the paranoids, whose performance appears to be adversely affected by an increase in the number of dimensions relevant to response selection.

Problems in the interpretation of cognitive abnormalities in schizophrenia

This study compared matched groups of patients with acute schizophrenia and with depression on three tests used in the assessment of schizophrenic thinking disorder. Most measures derived from these tests significantly differentiated the groups; however, within the schizophrenic group there were no significant correlations between scores on the three tests. Further data were available from a choice reaction-time card-sorting task, from which estimates of distractability, stimulus decision time, response decision time, and movement time, were obtained. Only one significant relation was found between these measures and scores on the clinical tests. The possible confounding effects of intelligence and responsiveness are discussed. It is argued that more direct measures of the latter are preferable to interpreting tests of thinking disorder in terms of information processing deficits.

Information Processing Components of Digit Symbol Performance in Schizophrenia

The present report is of the relationship between digit symbol performance in schizophrenia and measures derived from a visual choice reaction-time task. The ability to ignore irrelevant visual stimuli was most closely related to digit symbol performance, other measures adding little to the predicted variance.

'Filtering' and the cognitive deficit in schizophrenia

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.

Comparison of schizophrenics and normals on a visual search task

The response times of 16 paranoids, 16 nonparanoids and 16 normals were compared on a search task which required subjects to identify target letters embedded in displays of varying numbers of non-targets. The rate on increase in response times with increased numbers of letters displayed was not markedly different for the various groups, although a derived measure of decision and response-selection time indicated that normals selected responses more rapidly. When compared with normals, schizophrenics seemed to experience more difficulty in response selection and decision than in processing visual stimulus information.

Overinclusive thinking in mania and schizophrenia

Beginning with the work of Cameron (1944), the concept of overinclusive thinking has been used to describe or account for the thought disorder observed in schizophrenic patients. This is usually defined as an inability to preserve conceptual boundaries, perhaps based on a cerebral input dysfunction which causes difficulty in filtering stimuli (Payne et al., 1959; McGhie, 1970; Epstein, 1953; Broadbent, 1958). This leads the schizophrenic to make remote associations and to overgeneralize or overabstract.

Cognitive functioning in schizophrenia. I. Stimulus analysing and response selection processes

It has long been accepted that inadequate or abnormal cognitive performance is a characteristic of those patients described as schizophrenic (Cameron, 1938, 1939; Goldstein, 1939). A number of theories have been advanced to suggest that the basic deficit underlying this abnormal performance lies in impaired information processing. McGhie (1969, 1970) and Payne (1960) consider the defect to be in the filter that normally operates to exclude irrelevant stimuli, while Yates (1966a, 1966b) suggests that the impairment may reflect a slowed rate of information transfer in the primary processing channel. Hawks and Marshall (1971) also argue for slowed processing, but although they talk about overload due to inappropriately filtered input they appear to identify their position with Broen's (1968) response interference theory.