Cognitive mechanisms associated with clinical and non-clinical psychotic experiences

Abstract

The studies reported in this thesis were designed to address several important issues in symptom-specific cognitive models of psychosis. The design of these studies was guided by a commitment to the continuity hypothesis of psychosis, which holds that psychotic experiences exist on a continuum stretching into the healthy population. The thesis firstly examines a two-factor cognitive model of persecutory ideation, focusing primarily on the roles of thought suppression, intrusive thoughts, anxiety, social rank, and the jumping to conclusions bias. The thesis then turns to an examination of cognitive factors involved in hallucinations and, in particular, auditory verbal hallucinations. Chapters in this section describe a series of experimental and theoretical studies of the relations between intrusive thoughts and hallucinations, agency and hallucinations, and the role of inner speech in auditory verbal hallucinations. Two-factor models of persecutory delusion (PD) formation propose that in the first stage of PD formation an initial implausible idea is triggered. The second stage of Deformation is then the uncritical adoption of such a thought as a belief, which may be due to cognitive biases such as the jumping to conclusions (JTC) bias often present in those with PDs. The first study (Chapter 1) investigated whether thought suppression, and its interaction with anxiety, was associated with levels of non-clinical persecutory delusion like beliefs (PDLBs). It was hypothesised that thought suppression could play a role in the formation and maintenance of PDLBs through its tendency to lead to intrusive thoughts, and to trigger initial implausible ideas. Consistent with this proposal, thought suppression was positively associated with PDLBs only when anxiety was high. The second study (Chapter 2) examined a prediction of the two-factor model, namely that a second-stage factor, the jumping to conclusions (JTC) bias, should interact with first-stage factors, specifically social anxiety, social rank, anomalous experiences and thought suppression. Consistent with the two-factor model, the JTC bias was found not to be an independent predictor of PDLB levels, but its interaction with social rank was a significant predictor of PDLBs. It was concluded that although evidence was found for the two-factor model, the presence of the JTC bias was neither a sufficient nor necessary condition for PDLB formation. In addition to being postulated to play a role in persecutory delusion formation, intrusive thoughts have been implicated in the formation of hallucinations, and particularly auditory verbal hallucinations (AVHs). The third study (Chapter 3) created a new tool for assessing hypnagogic and hypnopompic (H&H) hallucinations, and showed that the presence of auditory H&H hallucinations, but not visual or felt-presence H&H hallucinations, was associated with a greater tendency to experience intrusions. The fourth study (Chapter 4) developed an extended model of AVHs in which rumination, as well as thought suppression, were proposed to be involved in the formation of AVHs, through their creation of intrusive thoughts. This model was tested in a healthy sample of individuals using structural equation modelling, and the proposed model was found to be a good fit to the data. The study on rumination and AVHs highlighted that agency disruption factors are likely to be involved in leading these self-generated cognitions to be experienced as alien. A theoretical analysis (Chapter 5) was made of the mechanisms likely to be involved in this disruption of agency, involving the concept of a neurocognitive action self-monitoring system (NASS) and a breakdown in the processes leading to the illusion of conscious will. A consideration was also given to how a Vygotskian conception of inner speech could contribute to inner speech models of AVHs. The next study (Chapter 6) then performed an empirical test of the proposal that the disruption of agency in AVHs is associated with a faulty NASS. Subliminal primes were used as a proxy for the predicted state proposed to exist in the NASS, which leads to the experience of agency. It was proposed that those prone to hallucinations would be less able to use primes to enhance their experience of agency, due to deficits in their NASS. A statistically significant trend was found for the more hallucination-prone to be less able to use subliminal primes, but this effect was only found in women. It was concluded that although this was a promising finding, the effect was too small and gender-specific to be practical to test in a clinical sample of patients with AVHs. The proposal that AVHs result from a breakdown in the NASS, specifically a corollary discharge deficit between speech production and reception areas, has been claimed to be supported by electrophysiological event-related potential (ERP) studies. However, only a simplistic conception of inner speech has thus far been investigated in ERP studies, and the potential confounding effects of attention have not been considered. The Nl ERP component response to auditory stimuli during inner speech was studied in as ample of healthy volunteers (Chapter 7). Although dampening of the Nl response was found during all types of inner speech, as compared to a silent baseline condition, dampening was also found during a mental rotation task. It was concluded that dampening of the Nl ERP component during inner speech is due to attention factors, and is not indicative of a corollary discharge mechanism. Finally, a theoretical analysis considers whether inner speech models of AVHs are able to satisfactorily account for the phenomenology of the experience (Chapter 8). It is concluded that subcategorisation of auditory hallucinations may be necessary, with memory-based, inner speech-based, and ictal-based models each accounting for a subcategory of auditory hallucinations. The concept of the dynamic developmental progression of AVHs is introduced and avenues for future research in this area highlighted