Depression is a global problem, causing disability and economic burden. Many people currently do not obtain treatment. Development of more accessible, cost-effective treatments is essential. An identified mechanism by which depression treatments work is through modifying underlying negative cognitive biases, which mediate changes in mood. A specific negative information-processing bias in depression is a tendency to interpret ambiguous facial expressions as sad rather than happy. The emotion recognition task is a treatment paradigm developed as a cognitive bias modification intervention to target this emotion recognition bias. Previous studies showed promising signs that this novel intervention could modify biases in people with low mood outside of laboratory conditions and potential to increase positive affect within laboratory conditions. The current study built on these developments, aiming to investigate, using a randomised controlled trial with follow-up at 2 and 6 weeks, whether a web-based version of the emotion recognition task could reduce depressive symptoms in addition to modifying emotion recognition biases. An analogue sample of 124 participants with low mood was recruited. Evidence was found that the intervention modified participants’ biases, compared to the control group but there was no evidence of improvement in mood. Study limitations included a high rate of attrition and non-adherence to the intervention. Future recommendations include modifying the intervention to increase acceptability, investigating generalizability of increased positive bias to different stimuli, and identifying consistent reductions in symptoms of depression before examining its efficacy with a clinical population.

The overarching aim of this thesis was to contribute towards the translation of a laboratory paradigm into a clinical intervention: that is, to develop a positive Cognitive Bias Modification (CBM) technique using mental imagery into an internet-based computerized intervention for people with clinical depression. Preliminary studies using an imagery-based CBM to modify interpretation bias in depression have shown significant effects of the CBM in alleviating depressive symptoms. We know very little, however, about the mechanisms underlying the beneficial effect of imagery-based CBM in depression. A particular focus of the current thesis was to explore the effects of imagery-based CBM on variables that were thought to contribute to symptom improvement: mental imagery, emotion and behaviour. Experiment 1 explored these effects in a sample of mildly depressed individuals, using a CBM paradigm in which participants were required to generate mental imagery in response to positive, negative or mixed (control) combinations of picture and word cues. Participants assigned to the positive imagery condition showed mood improvements as well as enhanced behavioural performance (fishing game task) and reduced cognitive bias compared to participants in the two other conditions. Further, positive imagery was rated as increasingly vivid as they went along with the training. Study 2 explored the possibility that the behavioural task (i.e. a fishing game) used in mildly depressed individuals to detect CBM-induced differences in behaviour could be associated with behavioural differences between individuals with various and clinical levels of depressive symptoms. The hypothesis was tested that in a sample of individuals with minimal to severe symptoms of depression, behavioural performance on the fishing game would be inversely related to the severity of their depressive symptoms. As predicted, participants with higher depression scores performed less well on the fishing game task than those with lower scores, and this association remained when controlling for other variables such as state mood. Experiment 3a and 3b constituted the first two pilot studies exploring the feasibility of delivering imagery-based CBM over the internet to individuals with clinical depression. In Experiment 3a, the imagery-based CBM was developed into an internet-based intervention involving 6 sessions of CBM that participants completed in their own home over a week. The Oxford Imagery Generation (OxIGen) program was piloted in a small sample (N = 6) of clinically depressed individuals, and qualitative data were collected to assess experience of the intervention. As a result, refinements were made to improve the intervention and enhance engagement. In Experiment 3b, the finalised version of the OxIGen program, which involved 12 sessions of online CBM completed over a month, was piloted in a small sample (N = 8) of individuals with clinical depression. Results showed high levels of acceptability and adherence. Three of the four participants allocated to the positive imagery version of OxIGen showed reliable levels of symptom improvement. The exploration of the effects of OxIGen on mental imagery, bias and behaviour provided a mixed picture. For example, the predicted change in vividness for positive future imagery and negative interpretative bias was only found in two of the four participants from the positive imagery group. Finally in Experiment 4, the effects of OxIGen on positive future imagery and behaviour were examined as part of a wider clinical trial involving a large sample (N = 150) of individuals with clinical depression. The larger scale of this study allowed a sufficiently powered test of the prediction that the intervention would lead to changes in specific features of imagery (i.e. vividness and likelihood of positive future imagery) and increases in behavioural activation. Further, the hypothesised link between positive future imagery and optimism was tested. The results examined whether the OxIGen intervention can induce changes at different levels of psychological functioning (i.e. emotional, cognitive and behavioural). It is discussed that the combined action of these changes may reinstate a positive feedback cycle that ultimately leads to symptom improvements. Existing resources are largely insufficient to combat the major health problem of depression. The development of a promising laboratory paradigm towards a clinical intervention is an important step towards the development of short and inexpensive forms of treatment that can be delivered to the hands of the many people who need help.