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Biomedical subjects

D R Hemsley

Publications and source records attributed to D R Hemsley.

At least 19 recordsLinked to original sources
PubMed1992

Loss of the Kamin blocking effect in acute but not chronic schizophrenics.

Differences between research diagnostic criteria (RDC)-diagnosed acute and chronic schizophrenics and normal controls were studied using a Kamin blocking procedure. Blocking is an established animal learning procedure, thought by some researchers to reflect selective attention; decreased blocking indicates increased processing of irrelevant stimuli. It was predicted that this pattern would be obtained in acute schizophrenics, tested soon after admission, for two reasons: (1) evidence from previous clinical studies indicates that acute schizophrenics are more aware of nonsalient aspects of their environment than controls; and (2) blocking is disrupted in animals in a hyperdopaminergic state and restored by neuroleptic medication. This was the case: acute, but not chronic, schizophrenics showed disrupted blocking. This disruption was especially clear in those acute schizophrenics tested within 2 weeks of hospital admission. By the second test session (in a cross-over design), there was some evidence of normalization in performance in the acute schizophrenics. These findings are considered with regard to the dopamine hypothesis of schizophrenia.

Acute Disease↗
PubMed1992

Gestalt perception in schizophrenia.

An experiment is described which investigates perceptual processing in schizophrenia. It examines the extent to which subjects employ top-down and bottom-up processing strategies in the interpretation of tachistoscopically presented images. The findings support the hypothesis that schizophrenic subjects do not benefit as controls do from the use of automatic, top-down processing of deeper level stimuli containing semantic information. However, it illustrates that, given sufficient processing time (up to 1000 ms), schizophrenics are able to compensate for this deficit by employing a bottom-up strategy requiring longer processing time. The findings suggest that the specific processing abnormalities in schizophrenia are amenable to detailed measurement, and some suggestions are made for further investigation.

Adult↗
PubMed1992

Abolition of latent inhibition by a single 5 mg dose of d-amphetamine in man.

The performance of healthy volunteer subjects on an auditory latent inhibition (LI) paradigm was assessed following administration of a single oral dose of d-amphetamine or placebo. It was predicted that a low (5 mg), but not a high (10 mg), dose of d-amphetamine would disrupt LI. The prediction was supported with left ear presentation of the preexposed stimulus only. When the preexposed stimulus was presented to the right ear the predicted pattern of findings was not obtained. It is concluded that the dopaminergic system is involved in the mediation of LI in man and it is speculated that the interaction between amphetamine dose and ear of presentation of the preexposed stimulus may reflect normally occurring dopaminergic hemisphere asymmetry.

Acoustic Stimulation↗
PubMed1991

Reasoning in deluded schizophrenic and paranoid patients. Biases in performance on a probabilistic inference task.

An experiment is described in which deluded subjects with a diagnosis of schizophrenia or of delusional disorder (paranoia) were compared with a nondeluded psychiatric control group and a normal control group on a probabilistic inference task. Factors relevant to belief formation and maintenance were investigated. Deluded subjects requested less information before reaching a decision and were more ready to change their estimates of the likelihood of an event when confronted with potentially disconfirmatory information. No differences were found between the two diagnostic groups of deluded subjects. The results are discussed in light of prevailing theories of the importance of abnormal experience rather than reasoning biases in the formation and maintenance of delusional beliefs. It is suggested that a reasoning abnormality is involved, which may coexist with perceptual abnormalities.

Adolescent↗
PubMed1991

Contextual effects on choice reaction time and accuracy in acute and chronic schizophrenics. Impairment in selective attention or in the influence of prior learning?

Two hypotheses were tested concerning the nature of the cognitive dysfunction in schizophrenia: (a) that there is a broadening of selective attention; and (b) that there is an impairment in associational learning. RDC-diagnosed acute and chronic schizophrenics and normal controls carried out a choice reaction time (RT) task in which conflict between the correct response to a target (a letter in the centre of a computer screen) and that cued by simultaneously presented flankers (two letters either side of the target) increased RT. For 80 ('valid') trials, flankers and targets were consistent in the response cued (pressing a button with either left or right hand); on 8 ('invalid') trials they conflicted. On invalid trials there was a slowing of RT, and an increase of errors for left-hand responses. Chronic schizophrenics showed the same reactions to cue validity as normal controls, both groups differing significantly from acute schizophrenics. For the latter, the RT data supported hypothesis (b), but the error rates appeared to support hypothesis (a).

Acute Disease↗
PubMed1990

Interhemispheric transfer of information and schizophrenia.

The interhemispheric transfer of stereognostic information was investigated in four groups of subjects: paranoid schizophrenics, non-paranoid schizophrenics, non-schizophrenic psychiatric patients, and normals. Previous work has raised the possibility that schizophrenia is characterised by a dysfunction of the corpus callosum, but there are several methodological problems associated with this research. A comparison of inter-manual and same-hand conditions on the experimental task revealed no evidence for impaired transfer of information in the schizophrenic groups. However, the performance of the non-paranoid schizophrenic group was markedly inferior to all other groups on the right hand/right hand no transfer condition, consistent with a left hemisphere dysfunction. Possible reasons for the failure to replicate previous findings are discussed.

Adult↗
PubMed1990

The Kamin blocking effect, incidental learning and psychoticism.

The Kamin blocking effect consists in impaired learning of an association between a conditioned stimulus (CS2) and an unconditioned stimulus (UCS) if CS2 is presented simultaneously with a different CS (CS1) already associated with the UCS. It is well established with animal but not human subjects. In the two experiments presented here, the effect was clearly demonstrated with UCS = a computer-presented yellow square, CS1 = a blue square and CS2 = a noise (Expt 1) or two smaller white squares (Expt 2). The Kamin effect has, by some theorists, been attributed to switching of attention away from CS2, which conveys only redundant information. If so, the size of the effect should co-vary with indices of selective attention commonly used with human subjects. As predicted, the blocking effect was found to be smaller in subjects who displayed a high degree of incidental learning in either of two tasks in which intentional vs. incidental learning corresponded to (1) words vs. word position, or (2) a target initial word letter vs. non-target initial letters. We report elsewhere that the blocking effect is absent in acute schizophrenics. In the present experiments, however, there was no systematic relation between any of four measures of psychoticism, or intelligence, and either the blocking effect or incidental learning.

Adult↗
PubMed1977

Lowered responsiveness and auditory signal detectability during depression.

Ten depressed patients were assessed on an auditory signal detection task; testing was repeated on remission. The patients' clinical state was monitored by means of the Hamilton rating scale and the Beck Depression Inventory. The task was performed under three conditions: 2 button (Yes/No); 1 button (Yes); 1 button (No). The findings indicated lower motor responsiveness during depression, consistent with Seligman's learned helplessness model. The measure of auditory sensitivity was also lowered during depression, possibly attributable to attentional disturbance. It is suggested that the lowered initiation of voluntary responses may be an important factor in the assessment of cognitive functioning during depression; such deficits may be reduced if the task does not permit the omission of a response.

Auditory Perception↗
PubMed1977

The influence of context on language perception in schizophrenia.

The present experiment employed the 'Cloze' procedure to investigate language perception in schizophrenia. The stimulus immediacy hypothesis of Salzinger, Portnoy & Feldman (1966) predicts that with increasing context, schizophrenic performance, unlike that of normals, will fail to improve. A comparison of groups of schizophrenics and normals on such a task, with varying levels of context, not only showed that schizophrenics failed to improve with greater context but that their performance deteriorated. A comparison of acute and chronic schizophrenics indicated that deterioration was most prominent in acute patients, the performance of chronics remaining relatively stable. An interpretation of the data in terms of narrowed the performance of chronics remaining relatively stable. An interpretation of the data in terms of narrowed attention in chronic schizophrenia appears plausible, and consistent with Broen's (1968) theory. Such an interpretation may be 'tested by an extension of the range of context conditions.

Acute Disease↗
PubMed1977

What have cognitive deficits to do with schizophrenic symptoms?

This paper considers possible relationships between cognitive deficits and symptomatology in schizophrenia. It is argued that a combination of defective filtering and slowness in response selection results in a state of information overload in acute schizophrenia. The methods by which normal subjects adapt to experimenter-induced overload may therefore be relevant to aspects of schizophrenic behaviour. The considerable intra- and inter-subject variability in symptomatology of schizophrenic patients may represent differeing adaptations to similar cognitive disturbance, such secondary abnormalities being prominent in chronic patients. Sections of the literature on acute-chronic differences are consistent with such a formulation, although one cannot infer intra-individual change from cross-sectional studies; there is a clear need for longitudinal investigations in this area. The preferred method of adaptation will be dependent on the severity of overload, the environment, and personality factors independent of the psychosis. The implications for the modification of schizophrenics' behavioural abnormalities by operant procedures are discussed.

Acute Disease↗
PubMed1976

Language behaviour in acute and chronic schizophrenia.

A predicition made by Broen (1968) regarding the performance of acute and chronic non-paranoid schizophrenics on measures of dominant verbal response bias was tested in a group of 40 hospitalized schizophrenic patients. A subgroup of 10 chronic patients were found to show an abnormal dominant response bias on two different language tasks and on one task showed a bias significantly greater than that shown by a group of 10 acute patients matched on verbal IQ and rated symptomatology. A correlational analysis of the bias scores of the total sample in relation to three indices of chronicity also showed a trend in the predicted direction of a greater dominant response bias with increasing chronicity. The data are consistent with Broen's (1968) theory of dominant response bias as a learned defence against aversive response interference in acute schizophrenia.

Acute Disease↗
PubMed1976

Attention and information processing in schizophrenia.

The performance of 20 acute schizophrenics and 10 depressives, matched for age, verbal intelligence, and pre-morbid functioning, was assessed on a choice reaction-time card-sorting task. Stimulus and response uncertainty were varied independently, and there were two main conditions, distraction and no distraction. The schizophrenics were slower than the depressives over all the functions examined in the study. Schizophrenics were significantly more affected by increases in response uncertainty than the depressives. Although there was a tendency for the schizophrenic group to be more affected by distraction and by increasing stimulus uncertainty, these differences were not significant. There was no significant interaction between the effects of stimulus and response uncertainty, nor between the effects of distraction and stimulus uncertainty. The effects of distraction increased with increasing response uncertainty. The results are discussed in relation to two models of information processing, suggested by Broadbent (1971) and by Sternberg (1969). Such models allow a more detailed examination of the cognitive abnormalities found in schizophrenia.

Adult↗
PubMed1976

'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.

Adult↗
PubMed1976

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.

Acute Disease↗