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The Journal of Neuroscience, July 5, 2006, 26(27):7265-7271; doi:10.1523/JNEUROSCI.1138-06.2006

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Behavioral/Systems/Cognitive
On Measuring the Perceived Onsets of Spontaneous Actions

Hakwan C. Lau,^1,2,3 Robert D. Rogers,⁴ and Richard E. Passingham^1,2

¹Wellcome Department of Imaging Neuroscience, University College London, London WC1N 3BG, United Kingdom, ²Department of Experimental Psychology, University of Oxford, ³Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, and ⁴Department of Psychiatry and Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford OX3 9DU, United Kingdom

Correspondence should be addressed to Hakwan C. Lau, Functional Imaging Laboratory, 12 Queen Square, London WC1N 3BG, UK. Email: h.lau{at}fil.ion.ucl.ac.uk

We investigated the neural mechanisms underlying the timing procedure that was devised by Libet et al. (1983) to measure the onset of conscious motor intentions in spontaneous actions. We previously showed that, when participants were required to estimate the onset of their intentions using this procedure, the activity in the presupplementary motor area (pre-SMA) was enhanced. Here, we show that when participants were required to estimate the onset of their motor executions (instead of their intentions), the activity in the cingulate motor area was enhanced. Across participants, the degree of this neural enhancement was correlated with the degree of perceptual bias: the higher the degree of enhancement, the earlier the perception. Analysis of data from a previous experiment suggests that the same principle holds true for the relationship between the perceived onset of intentions and the activity in the pre-SMA. We therefore argue that the timing method of Libet et al. (1983) is problematic, because the measuring process affects the neural representations of action and thus also the perceived onsets that the method is designed to measure.

Key words: attention; motor intention; motor; movement; motion; motor activity; fMRI; motor control

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Received July 25, 2005; revised April 30, 2006; accepted May 23, 2006.

Correspondence should be addressed to Hakwan C. Lau, Functional Imaging Laboratory, 12 Queen Square, London WC1N 3BG, UK. Email: h.lau{at}fil.ion.ucl.ac.uk

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