Degree Name

Doctor of Philosophy


School of Psychology


The adjustment process after a traumatic brain injury (TBI) is complex, individual and results in high levels of psychological distress as the individual comes to accept their post-injury self. This thesis undertakes a series of five studies to investigate whether Acceptance and Commitment Therapy (ACT) can facilitate psychological adjustment after a severe TBI. The first study provides a selective review of cognitive and psychological flexibility in the context of treatment for psychological distress after traumatic brain injury, with a focus on acceptance-based therapies. Cognitive flexibility is a component of executive function that is referred to mostly in the context of neuropsychological research and practice. Psychological flexibility, from a clinical psychology perspective, is linked to health and wellbeing and is an identified treatment outcome for therapies such as Acceptance and Commitment Therapy. People with a TBI often suffer impairments in their cognitive flexibility as a result of damage to areas controlling executive processes but have a positive response to therapies that promote psychological flexibility. Overall, psychological flexibility appears a more overarching construct and cognitive flexibility may be a subcomponent of it but not necessarily a pre-requisite. Study two is a Phase I clinical outcome research involving two case studies. The two men with severe TBI and associated psychological distress jointly engaged in a seven session treatment programme based on ACT principles. The intervention showed benefits with one participant, but was workable and showed acceptability with regard to programme content, measures and delivery mode for both participants. Significant changes pre to post intervention in measures of participation were not indicated. Qualitatively though, both participants engaged in committed action set in accordance with their values. This study suggests that ACT may be feasible in addressing psychological distress after a severe TBI and permitted the transition to the Phase II clinical trial. Study three reported the protocol for a single centre, two armed, Phase II Randomised Control Trial (RCT) to address the adjustment process following a severe TBI. The publication of the protocol before the trial results are available, addresses fidelity criterion (intervention design) for RCTs, ensures transparency and that it meets the guidelines according to the CONSORT statement. Study four presents preliminary validation data on both the Acceptance and Action Questionnaire – Acquired Brain Injury (AAQ-ABI) and the Acceptance and Action Questionnaire – II (AAQ-II). Data from 150 participants with ABI was subject to exploratory factor analysis on the AAQ-ABI (15 items). A subset of 75 participants with ABI completed a larger battery of measures to test construct validity for the AAQ-ABI and to undertake a confirmatory factor analysis on the AAQ-II (7 items). The results suggest both measures can be used with individuals following an ABI but they index different facets of psychological flexibility. Study five involved the implementation of the RCT reported in study three. A total of 19 participants were randomly allocated to either a seven session ACT or Befriending (active control) intervention. Outcome measures included psychological flexibility, participation and measures of psychological distress. A repeated measures ANOVA indicated significant decreases in levels of both depression and stress when compared to the active control group. The five studies contribute to the clinical outcome research after severe TBI and show initial efficacy for ACT to decrease psychological distress and facilitate psychological adjustment for this client group but the mechanisms of change are undetermined.