Pappa, Elisavet; (2025) Psychosis and Illusory Social Experiences: Phenomenology, Cognitive Mechanisms and Social Functioning. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A hallmark of psychosis is the frequent occurrence of illusory social experiences within positive symptoms. The phenomenology of delusions and hallucinations reveals that individuals with psychosis often perceive and interact with 'illusory social agents’. Despite this, a thorough exploration and explanation of social phenomenology, particularly in delusions, remains lacking. This thesis aims to address this gap by enhancing our understanding of the phenomenology and socio-cognitive mechanisms underlying delusional symptoms. The first study involves two comprehensive systematic reviews and metaanalyses, one using validated measures of delusions and the other including ad-hoc measures, to estimate the prevalence of delusional themes in psychosis. These analyses demonstrate that social elements are prevalent across cultures, clinical diagnoses, and time periods. Although much research has focused on illusory social agents in auditory hallucinations, less attention has been given to delusional agents beyond persecutors. Therefore, the second study examines delusions using a large-scale medical records database, identifying the characteristics of illusory social agents in delusions. Most of these agents are human and identifiable as either individuals or groups. The third study investigates potential cognitive mechanisms underlying these experiences by employing interactive game-theory tasks to assess agency detection. Individuals with psychosis and high paranoia tend to over-detect human agency in interactions with human players and under-detect it with computer players, compared to controls. This suggests that a bias in agency detection may be a key mechanism contributing to social cognition dysfunction in psychosis. Finally, agent-based modelling is used to evaluate the impact of illusory social agents on social success within populations. Illusory social experiences reduce fitness under some conditions in cooperative scenarios, but not in anti-cooperative ones. Furthermore, the interaction between heightened agency and psychosis is linked to increased fitness, suggesting that some mechanisms underlying hyper-agency detection may be evolutionarily adaptive in specific contexts.

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