Abstract
Human voluntary actions are often associated with a distinctive subjective experience termed ‘sense of agency’. This experience could be a reconstructive inference triggered by monitoring one's actions and their outcomes, or a read-out of brain processes related to action preparation, or some hybrid of these. Participants pressed a key with the right index finger at a time of their own choice, while viewing a rotating clock. Occasionally they received a mild shock on the same finger. They were instructed to press the key as quickly as possible if they felt a shock. On some trials, trains of subliminal shocks were also delivered, to investigate whether such subliminal cues could influence the initiation of voluntary actions, or the subjective experience of such actions. Participants' keypress were always followed by a tone 250 ms later. At the end of each trial they reported the time of the keypress using the rotating clock display. Shifts in the perceived time of the action towards the following tone, compared to a baseline condition containing only a keypress but no tone, were taken as implicit measures of sense of agency. The subliminal shock train enhanced this “action binding” effect in healthy participants, relative to trials without such shocks. This difference could not be attributed to retrospective inference, since the perceptual events were identical in both trial types. Further, we tested the same paradigm in a patient with anarchic hand syndrome (AHS). Subliminal shocks again enhanced our measure of sense of agency in the unaffected hand, but had a reversed effect on the ‘anarchic’ hand. These findings suggest an interaction between internal volitional signals and external cues afforded by the external environment. Damage to the neural pathways that mediate interactions between internal states and the outside world may explain some of the clinical signs of AHS.
Highlights
Voluntary actions can be functionally defined by two key properties: they are internally-generated, as opposed to triggered by external stimuli, and they are often goal-directed (Passingham, Bengtsson, & Lau, 2010)
These two views make different predictions about how external stimuli might influence the experience of agency: If experience of agency is merely a reconstructive inference, interventions which influence brain processes preceding a voluntary action should have no influence on one's sense of agency, unless those interventions generate some perceptual event which can figure in the inference
We developed a novel paradigm to investigate the contribution of precursor signals of endogenous actions to sense of agency
Summary
Voluntary actions can be functionally defined by two key properties: they are internally-generated, as opposed to triggered by external stimuli, and they are often goal-directed (Passingham, Bengtsson, & Lau, 2010) They are associated with two specific subjective experiences: an experience of volition, and an experience of agency. Experience of agency could depend on a readout of brain processes in frontal (Fried, Mukamel, & Kreiman, 2011) and/or parietal areas (Desmurget et al, 2009) that precede voluntary action These two views make different predictions about how external stimuli might influence the experience of agency: If experience of agency is merely a reconstructive inference, interventions which influence brain processes preceding a voluntary action should have no influence on one's sense of agency, unless those interventions generate some perceptual event which can figure in the inference. If experience of agency depends on internal precursor signals that drive voluntary action, any intervention that influences these signals may affect experience of agency, whether the intervention is consciously perceived or not
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