Changes in cognition are thought to contribute to the development and/or maintenance
of depression and anxiety disorders. In theory, cognitive behavioural therapy, the most
common psychological therapy for depression and anxiety, exerts its effect through
modifying cognitive biases observed in patients. Most of the evidence about cognition
underpinning depression/anxiety comes from self-reported questionnaires and clinicianrated scales. As an addition to current measurement tools, cognitive tasks could possibly
be integrated with clinical practice as more objective and more precise measures of
cognition. This, however, requires the development of tasks that measure clinically
relevant cognitive processes. As an initial step towards this, in the first two experimental
chapters I present results about the association between depression/anxiety symptoms
and performance on a battery of cognitive tasks. I found in the first study as well as in
the follow-up replication study and mega-analysis that participants with higher
depression/anxiety symptom scores were faster at identifying changes in images in a
change blindness task. This suggests that change blindness could possibly be used as a
behavioural signature for attentional mechanisms underlying depression/anxiety. In the
third experimental chapter I examine whether this effect is present in a case-control
study. In addition, I investigate metacognitive processes in patients vs. healthy controls,
which could have implications for mechanisms underlying psychological therapy. There
was no evidence for change blindness and metacognition effects although this final pilot
study included in the thesis did not have adequate power to detect effect sizes in the
range typically observed in clinical literature. Overall, this thesis presents the research
process through which cognitive tasks relevant to the treatment of depression and
anxiety could be identified, and makes a case for the potential benefits of integrating cognitive tasks with psychological therapy as assessment and potentially even
therapeutic tools as means to improve personalised treatment.