This thesis sets out to explore how two preconditions for goal-directed behaviour might arise from neural activity—the capacity to integrate information about a stimulus to inform action-selection, and the capacity to resolve conflict in the presence of competing alternatives. I examine this over the course of three empirical studies incorporating behavioural measures, computational modelling, magneto- and electroencephalography (M/EEG), functional Magnetic Resonance Imaging (fMRI), as well as both univariate and multivariate analysis techniques. In the Introduction, I introduce the background to and motivation for the thesis, exploring the evidence accumulation framework as a tool to understand the latent cognitive processes involved in adaptive action-selection, and exploring the phenomenon of conflict resolution through the lens of the Stroop task.

In Chapter 2, I asked how different kinds of task difficulty influence the neural process of accumulating evidence in service of an action. I used an Evidence Accumulation Model (EAM) and combined magneto- and electroencephalography (M/EEG) to explore the impact of manipulating perceptual difficulty and the difficulty of categorising the percept according to a rule. I used multivariate pattern analysis (MVPA) to quantify how information, latent in the neural activity, about the percept, rule, the application of the percept to the rule (decision), and the response, varied across the manipulations. Manipulating perceptual difficulty influenced the model parameter associated with, and hallmark neural signals of, evidence accumulation as well as information relating to the percept, decision, and response. In contrast, manipulating categorisation difficulty influenced the model parameter associated with the amount of evidence required to make a decision, had a subtler effect on ramping neural activity, and only influenced information relating to the decision and response. Together the results gesture at multiple underlying processes within the evidence accumulation process that are affected differently by a manipulation of perceptual evidence relative to manipulating the difficulty of evaluating the percept according to a rule.

In Chapters 3 and 4, I asked how conflict in the arc from perception to action is resolved: though the inhibition of task-irrelevant information, the enhancement of relevant information, or a combination of both. In Chapter 3, I developed variations of the classic Stroop task suitable for a subsequent fMRI investigation to detect neural processes of inhibition and enhancement in the Stroop task. This comprised a novel baseline condition in which participants named the sizes of Stroop (word-colour) stimuli, and a baseline condition in which participants named the colours of non-words matched to Stroop stimuli for low-level visual features. In both cases, less interference should be produced by the irrelevant stimulus features relative to the Stroop, modulating the need for neural inhibition and/or enhancement relative to the more interfering Stroop task. I validated the baselines behaviourally in both manual and vocal versions of the tasks, demonstrating that interference was reduced relative to the Stroop task, and this effect was greater in the vocal than the manual versions of the tasks.

In Chapter 4, I used the baseline tasks developed in Chapter 3 in an fMRI study exploring inhibition and enhancement in the Stroop task. I used MVPA to quantify the latent word-related information in word-specialised cortex and colour-related information in colour-specialised cortex, as well as the word- and colour- information available in frontoparietal “multiple demand” (MD) regions. I found initial evidence to support the notion that the brain inhibits task-irrelevant word information in word-sensitive cortex during the task, but no evidence to suggest that the brain enhances task-relevant colour information in colour-sensitive cortex. I replicated findings that frontoparietal MD regions preferentially maintain task-relevant information, but found no evidence to discriminate whether this was achieved by enhancement or inhibition of information in MD. The findings suggest that the brain prioritises task-relevant information in MD region, and this may be associated with inhibition of task-irrelevant information in specialised cortex when there is conflict in the arc from perception to action.

The thesis concludes with a discussion of the limitations and future directions for research in the field of cognitive control, decision-making, and attentional processes, alongside the potential of using MVPA and EAMs to further our understanding of these complex neural processes.