Brown, Tracey; (2002) An investigation into illusory conjunctions and context-processing in schizophrenia: Differential relationships between symptoms. Doctoral thesis (D.Clin.Psy), UCL (University College London).

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Abstract

The context processing theory of schizophrenia proposes that when processing information, there is a dedicated mechanism used to select task appropriate responses over task irrelevant ones. It is suggested that in schizophrenia there is a weakening of context processing mechanisms, which causes irrelevant information to be attended to and given greater significance than is required. An illusory conjunction task was designed to test the hypothesis that people with schizophrenia perform differently on context-sensitive tasks to non-psychiatric controls. As it has been suggested that context processing is more deficient in certain sub-types of schizophrenia it was further hypothesised that patients categorised into 'poverty', 'reality distortion' and 'disorganised' symptoms would have significant differences in their performance and that acute symptoms of schizophrenia would see more illusory conjunctions than those with chronic symptoms. 41 patients with schizophrenia and 24 non-psychiatric controls were briefly presented with vertical rows of objects comprised of different coloured squares, circles and triangles and had to indicate if they had seen a red triangle amongst the objects. Presentation times were brief and additional tasks were included to increase processing demands, thereby increasing the likelihood of an illusory conjunction. Results showed that there were significantly more illusory conjunctions, target errors and total errors overall for the schizophrenic group than for the non-psychiatric controls (f=25.43, df=l,63, p<0.04, f=5.29, df=l,63, p<0.02; f=9.92, df=l,63, p<0.00 respectively). As the attention load increased over the three conditions there were more illusory conjunctions seen for the schizophrenic group than for the non-psychiatric controls2(f=3.37, df=2,62, p<0.04). However there were no significant differences between the three symptom sub-groups of schizophrenia and there were no significant differences between acute symptoms and chronic symptoms. Results were further discussed in relation to the context processing theory, and previous research showing similar results in people with acquired brain damage. Questions arose as to whether context processing mechanisms are related to the parietal lobes and its involvement in 'diathesis-stress' models of schizophrenia.

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