Under normal circumstances we consciously attribute authorship of our actions to ourselves, the sensation of agency. We describe an experiment where participants observed a virtual human character speak and falsely attributed the speaking to themselves. They later shifted the FF of their own voice toward the stimulus voice. This only occurred when the life-sized VB substituted their own and moved with their own movements. A further contribution to the effect was vibrotactile stimulation on the thyroid cartilage synchronized with the speaking. This suggests that agency can be self-attributed even in the absence of prior intention, feed-forward prediction, priming, and cause preceding effect. A critical contributor is the illusion of ownership over the VB that spoke.

Abstract

When we carry out an act, we typically attribute the action to ourselves, the sense of agency. Explanations for agency include conscious prior intention to act, followed by observation of the sensory consequences; brain activity that involves the feed-forward prediction of the consequences combined with rapid inverse motor prediction to fine-tune the action in real time; priming where there is, e.g., a prior command to perform the act; a cause (the intention to act) preceding the effect (the results of the action); and common-sense rules of attribution of physical causality satisfied. We describe an experiment where participants falsely attributed an act to themselves under conditions that apparently cannot be explained by these theories. A life-sized virtual body (VB) seen from the first-person perspective in 3D stereo, as if substituting the real body, was used to induce the illusion of ownership over the VB. Half of the 44 experimental participants experienced VB movements that were synchronous with their own movements (sync), and the other half asynchronous (async). The VB, seen in a mirror, spoke with corresponding lip movements, and for half of the participants this was accompanied by synchronous vibrotactile stimulation on the thyroid cartilage (Von) but this was not so for the other half. Participants experiencing sync misattributed the speaking to themselves and also shifted the fundamental frequency of their later utterances toward the stimulus voice. Von also contributed to these results. We show that these findings can be explained by current theories of agency, provided that the critical role of ownership over the VB is taken into account.