Kondel, Tejinder Kaur; (2003) The role of executive functions in suggestibility. Doctoral thesis (D.Clin.Psy), UCL (University College London).

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Abstract

Clinical psychologists are frequently instructed by the courts to assess the ability of witnesses or of the accused to give reliable evidence. Many studies have reported an inverse relationship between IQ and memory and suggestibility (as measured by the Gudjonsson Suggestibility Scale: GSS 1 and 2; Gudjonsson 1984a, 1987b). This relationship has, however, generally been examined in diagnostically mixed samples of forensic psychiatric patients, court referrals and groups simply referred to as forensic. Such mixed, and indeed unspecified, sampling of forensic psychiatric patients could lead to increased heterogeneity and partly explain the difficulty with replicating some findings. The aim of the present study was to examine the relationship of cognitive deficits to suggestibility in a well-defined homogenous sample of forensic patients with a diagnosis of psychotic disorder. In particular, a major focus was to examine the relationship of specific executive functions to suggestibility - an area previously unexamined. Thirty-two subjects were divided into two groups (15 low and 17 high suggestible) as defined by their non-overlapping scores on the GSS 1 Yield 1 measure. This measure captures what might be termed pure suggestibility since it reflects the tendency of subjects to endorse false statements when under no interrogative pressure. The groups were tested on several measures of executive function, immediate and delayed memory (as measured by the GSS I), and the Wechsler Abbreviated Scale of Intelligence (WASI). Between - group comparison revealed that this measure of pure suggestibility was associated with a particular cognitive profile. Contrary to previous findings, the results revealed no significant differences between the high and low suggestibility groups in their IQ, or immediate and delayed memory scores. On tests of executive function, the high and low suggestibility groups did not differ in their working memory and response-inhibition performance, but the high suggestibility group did perform worse on tasks tapping rule-attainment. Theory of Mind and speed of decision-making. Moreover, two of the executive tasks that did produce differences between the groups (speed of decision-making and theory of mind) correlated with IQ and when this was partialled-out, the differences in these measures became non-significant. However, the differences in rule-attainment remained significant after covarying for IQ. It is proposed that the link between the rule-attainment task and high suggestibility reflects the greater tendency to guess in highly suggestible subjects. One important implication of this finding for clinicians is that another cognitive vulnerability (other than IQ and memory) may bring about susceptibility to suggestion. In future, when courts refer cases for issues concerning reliability of evidence, then not only is a detailed history required to detect any past episodes of mental illness, but certain cognitive tasks - especially measures of executive function such as the Brixton test may highlight a susceptibility to suggestion that is independent of and possibly precedes any suggestibility in response to interrogative pressure.

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