Fleming, S.M.; (2011) Criteria and awareness in perceptual decision. Doctoral thesis , UCL (University College London).

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Abstract

The immediacy of subjective experience belies the complex process of inference and categorisation that our brains undertake every moment of our waking lives, a process that allows the selection of the best course of action in the face of under-determined sensory input. There is much behavioural evidence that humans use the context in which decisions occur to actively shape links between perception and action. However, there are several remaining questions as to how this process occurs in the brain, and how such decision-making is linked to subjective reports, four of which are addressed in this thesis. It is unknown at which stage along the path from sensory to motor areas a loss function is integrated into the perceptual decision process. Using fMRI I show that asymmetries in value affect a fronto-parietal-basal ganglia network, rather than impacting upon the coding of visual categories. Theoretical models predict that the basal ganglia adjust the link between decision and action on the basis of contextual variables, but supporting empirical evidence is scarce. In two further imaging studies I show that the subthalamic nucleus modulates action control when default expectations are violated. That links between perception and action may be labile leads one to ask to what extent the observer has metacognitive access to these stages of the decision process, and which brain structures might mediate this access. I show that a second-order signal detection model can capture some, but not all, features of metacognitive confidence. Finally, I show that individual differences in metacognitive ability are associated with the structure of anterior prefrontal cortex. Comparing the levels of perceptual and metacognitive decision is critical for understanding how the mechanisms of decision-making are linked to awareness and self-report. The thesis concludes with a brief discussion of future challenges in this direction.

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