Filevich, E; (2013) Volition and inhibition: Objective and subjective aspects of human volitional control. Doctoral thesis , UCL (University College London).

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Abstract

Action decisions can be directly driven by the current state of the external environment (instructed decisions); or they can be driven by internal mental states and goals, independently of the current environment (intentional decisions). Neural, behavioural and subjective data suggests that two separate neural systems may drive instructed and intentional action respectively. The distinction can be generalized beyond action itself to action inhibition, also classifiable as either instructed or intentional. However, the validity of the instructed/intentional distinction remains controversial. This thesis presents three linked sets of experiments that explored the validity and generality of the distinction, extending it in two key directions: action inhibition and subjective experience. The first group of experiments concerned decision making processes related to action and inhibition; the second focused on the period between decision making and action execution and the third on the subjective experience of intentional actions. Decision making processes were addressed by comparing electrophysiological and subjective measures prior to, during and after decisions to act or inhibit action. In the absence of external imperatives, intentional decisions may capitalize on spontaneous neural fluctuations, and show a weaker neural code than their instructed counterparts. To further explore the relative strength of intentional decisions, the period between decision making and action execution was addressed with EEG and behavioural methods. No evidence for unstable intentional decisions was found, during decision maintenance. Intentional action decisions may be strong, and persistent. Finally, two experiments directly compared the subjective experience of intentional and instructed actions. Neuroimaging results revealed possible mechanisms associated with the subjective experience of acting intentionally. Together, results support the broad distinction between instructed and intentional decisions. In particular, the coding of intentional actions may involve partial activations of alternative responses. Importantly, the thesis also demonstrates the feasibility of experimental studies addressing the subjective experience of intentional behaviour.

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