Stimulus uncertainty, response uncertainty, and stimulus-response compatibility as determinants of schizophrenic reaction time performance

Environmental Adaptations Improve Everyday Action in Schizophrenia

Cognitive functioning, particularly executive functioning, is a strong predictor of functional outcomes in people with schizophrenia. Cognitive remediation has been shown to improve specific cognitive processes, but adjunctive interventions are required for meaningful gains in adaptive functioning, particularly in people with chronic illness. This study examined whether (and how) environmental adaptations, used without training, may circumvent cognitive difficulties and facilitate everyday task performance in individuals with chronic schizophrenia. Forty-two individuals with chronic schizophrenia/schizoaffective disorder were administered cognitive measures and two versions of the Naturalistic Action Test (NAT)-a standard version (ST-NAT), and a user-centered version (UC-NAT) that incorporated environmental adaptations designed to facilitate task performance. The NAT conditions were counterbalanced across participants. Analyses compared performance between the NAT versions and examined the cognitive correlates of each NAT condition. Individuals with schizophrenia made fewer errors on the UC-NAT as compared to the ST-NAT; this between-group difference was significant for all error types. Compared to the ST-NAT, the UC-NAT performance was not significantly associated with an executive function measure of planning. Environmental adaptations may be implemented without extensive training to improve everyday action in individuals with chronic schizophrenia. Environmental adaptations that reduce planning demands may be most effective in this population.

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.

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.

The prediction of rehabilitative success after three years. The use of social, symptom and cognitive variables

A three-year follow-up study of 49 psychiatric patients, representative of those found in long-stay care, tested whether behavioural, symptom and demographic variables as well as response-processing difficulties could predict levels of psychiatric care. The researchers were blind to the criteria for allocating patients to particular forms of care and the staff responsible for care had no access to information collected by the research team. Not only was it possible, using only these few factors, to predict the form of care, but one factor, response processing, was related to whether patients moved to more independent forms of psychiatric care.

Tactile-evoked potentials in schizophrenia. Interhemispheric transfer and drug effects

EEG potentials evoked by tactile stimulation of the forearm (tactile-evoked potentials or TEPs) were recorded simultaneously from both cerebral hemispheres in a group of schizophrenics and a group of healthy control subjects. Differences between the groups were found for the early waves of the TEPs: in the control subjects the first two positive waves (P25 and P50) and the first negative wave (N35) recorded from the hemisphere on the same side as the stimulation were slower (i.e. had longer latency) than those recorded from the hemisphere contralateral to the stimulation. This 'lateralization effect' was not seen in the schizophrenic subjects. It was concluded that the TEPs recorded from the hemisphere ipsilateral to the stimulus were not being transmitted from the other hemisphere via the corpus callosum and must therefore have been transmitted via direct ipsilateral pathways from the periphery. In a second experiment the drug pindolol was administered to schizophrenic subjects but differences in P50 latency between ipsilateral and contralateral hemispheres were found equally in both drug and placebo groups. We also found slight evidence to suggest that the more severely ill the patient the more similar the TEP latencies recorded from the contralateral and the ipsilateral hemispheres.

Perceptual deficit in schizophrenia: a defect in redundancy utilization, filtering or scanning?

The perception by schizophrenic patients of stimuli with more than one feature (dimension) was investigated using psychiatric and non-psychiatric control groups. Indices of the ability (a) to make use of redundant stimulus cues, (b) to 'screen out' or filter irrelevant stimulus features, and (c) to scan the perceptual field for relevant stimulus features, indicated that only filtering was consistently poor in schizophrenia. It has been suggested that the schizophrenic patient may tend to perceive his environment in an undifferentiated holistic manner rather than in an analytic manner and the implication for the theory of left hemisphere pathology in schizophrenia is discussed. However, the performance of the schizophrenic subjects did not differ significantly from that of the group of depressed patients, which suggests that the selective attention deficits previously observed in schizophrenia are not specific to the disorder.