Is consciousness required to withhold an impending action?: Evidence from event-­related brain potentials

Hughes, Gethin. 2008. Is consciousness required to withhold an impending action?: Evidence from event-­related brain potentials. Doctoral thesis, Goldsmiths, University of London [Thesis]

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Abstract or Description

This thesis explores whether a decision to withhold an impending motor action can be initiated unconsciously. There is much evidence to suggest that both voluntary actions and reactions to external events can be initiated without consciousness. However, there is some debate as to whether inhibition or control of behaviour can occur unconsciously. Libet et al. (1985) proposed that while consciousness is not required to initiate an action, it may be essential in allowing the action to be vetoed. Similarly, evidence from tasks involving response conflict points to a close association between inhibition/control of behaviour and conscious awareness. In particular, both fMRI and EEG correlates of control are seen to be absent when response conflict is unconscious.

The research in this thesis aimed to clarify whether the no-go N2 and P3, ERP correlates of the no-go response, can be modulated by an unconscious prime. In each of five EEG experiments, target-related N2 and P3 components were significantly affected by the nature of the unconscious primes. More specifically, when the unconscious information coded for a no­go response, N2 and P3 amplitude was significantly reduced, suggesting that inhibition of the imminent response was primed by the unconscious stimuli. In addition, there was evidence that the unconscious primes were able to directly engage frontal inhibition/control mechanisms. In experiments 1, 2 and 5 early ERP differences were observed over frontocentral electrodes that were entirely dependent on the nature of the unconscious prime. Furthermore, experiment 5 showed that this early modulation of ERP activity was directly related to the extent to which the participants were influenced by the unconscious primes. These findings suggest that inhibition of an impending motor action can be initiated by an unconscious stimulus. These conclusions are discussed in relation to previous research, and the possible role of consciousness in behaviour. The limitations of the current research and suggestions for future work are also considered.

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Thesis (Doctoral)

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consciousness; event­related brain potentials; free will

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Date Deposited:

07 Jul 2020 15:01

Last Modified:

08 Sep 2022 12:50


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