Pathways to Psychosis
: Examining the Effect of Childhood Trauma and Abnormal Belief-Updating Processes on Psychosis

  • Jazz Croft

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


There is a body of evidence showing that childhood trauma is associated with psychotic experiences (PEs). Establishing whether this association is causal and what mechanisms mediate this relationship is needed to understand how psychosis develops and help inform interventions to mitigate the risk of PEs.

The first study in this thesis investigates whether exposure to interpersonal violence and neglect is causally associated with PEs, whether there are sensitive periods of exposure, and if different types of trauma are differentially associated with PEs. The subsequent studies in this thesis examine whether information-processing biases are associated both with trauma and PEs, and whether these biases lie on the causal pathway from trauma to PEs.

Analyses were carried out using data from ALSPAC, a large UK birth cohort. A systematic review and meta-analysis of childhood trauma and psychosis-related information-processing biases was also conducted.

Childhood trauma was associated with PEs and this was largely unchanged after adjustment for confounders. The greatest increase in PE risk was associated with exposure to multiple types of trauma, consistent with a dose-response relationship. There was little evidence to support the presence of sensitive periods of risk or of differential effects of specific types of trauma. When examining information-processing biases I found that an increased expectation of change (reversal) and sub-optimal belief-updating (decision noise) were associated with PEs, and not explained by confounding. Childhood trauma was also associated with greater decision noise, but not with the other belief-updating processes examined. However, there was little evidence that decision noise mediated the relationship between trauma and PEs. The systematic review provided some evidence that childhood trauma is associated with a bias to attribute the cause of events to external factors, but not with the other biases examined.

I conclude the thesis with a critical evaluation of the results, within the context of the studies’ strengths and limitations, and discuss the extent to which they support a causal relationship between exposure to trauma and PEs, and whether abnormal-belief updating processes are on this hypothesised pathway.

Further research should utilise interdisciplinary approaches and longitudinal data to establish what mechanisms contribute to the psychosis pathway in order to identify targets for intervention that can mitigate the effect of trauma exposure on PE and other mental health outcomes.

Date of Award23 Jun 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorStanley Zammit (Supervisor), Jon E Heron (Supervisor) & Christoph Teufel (Supervisor)


  • psychiatry
  • trauma
  • cognitive biases

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