Abstract
Brain-machine interfaces (BMI) allows individuals to control an external device by controlling their own brain activity, without requiring bodily or muscle movements. Performing voluntary movements is associated with the experience of agency ("sense of agency") over those movements and their outcomes. When people voluntarily control a BMI, they should likewise experience a sense of agency. However, using a BMI to act presents several differences compared to normal movements. In particular, BMIs lack sensorimotor feedback, afford lower controllability and are associated with increased cognitive fatigue. Here, we explored how these different factors influence the sense of agency across two studies in which participants learned to control a robotic hand through motor imagery decoded online through electroencephalography. We observed that the lack of sensorimotor information when using a BMI did not appear to influence the sense of agency. We further observed that experiencing lower control over the BMI reduced the sense of agency. Finally, we observed that the better participants controlled the BMI, the greater was the appropriation of the robotic hand, as measured by body-ownership and agency scores. Results are discussed based on existing theories on the sense of agency in light of the importance of BMI technology for patients using prosthetic limbs.
Highlights
Most of our actions are automatic and triggered externally
feelings of agency or authorship (FoA) refers to a pre-reflective sensorimotor experience of being the author of an action, while judgments of agency (JoA) refers to the explicit declaration that
We investigated to what extent explicit and implicit sense of agency over Brain-machine interfaces (BMI)-generated actions and resulting outcomes influence the appropriation of the BMI device, as measured through the embodiment of the device
Summary
Most of our actions are automatic and triggered externally. Voluntary actions, because they are initiated endogenously on the basis of our intentions, are seen as a fundamental marker of human behaviour. Brain-machine interfaces and the sense of agency absence of sensory feedback during BMI-generated actions should reduce SoA in comparison with situations in which participants use their own hand to perform the action, since it involves either a reduction in the quality of predictions (i.e. the comparator model) or a reduced number of cues, since no reafferences are produced (i.e. the cue integration theory). In the body-generated action condition, participants used their right index finger to press a key whenever they chose so as to trigger a resulting tone They had to estimate, in milliseconds, the duration of the delay between their keypress and the tone (i.e. implicit SoA; [21]). At the end of the experiment, participants had to complete a questionnaire assessing the extent to which they felt the robotic hand was embodied, as well as their level of cognitive fatigue before and after each experimental condition
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