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. 2016 Sep 22:6:33514.
doi: 10.1038/srep33514.

Removal of proprioception by BCI raises a stronger body ownership illusion in control of a humanlike robot

Maryam Alimardani  1   2 , Shuichi Nishio  1 , Hiroshi Ishiguro  1   3
Affiliations

Removal of proprioception by BCI raises a stronger body ownership illusion in control of a humanlike robot

Maryam Alimardani et al. Sci Rep. .

Abstract

Body ownership illusions provide evidence that our sense of self is not coherent and can be extended to non-body objects. Studying about these illusions gives us practical tools to understand the brain mechanisms that underlie body recognition and the experience of self. We previously introduced an illusion of body ownership transfer (BOT) for operators of a very humanlike robot. This sensation of owning the robot's body was confirmed when operators controlled the robot either by performing the desired motion with their body (motion-control) or by employing a brain-computer interface (BCI) that translated motor imagery commands to robot movement (BCI-control). The interesting observation during BCI-control was that the illusion could be induced even with a noticeable delay in the BCI system. Temporal discrepancy has always shown critical weakening effects on body ownership illusions. However the delay-robustness of BOT during BCI-control raised a question about the interaction between the proprioceptive inputs and delayed visual feedback in agency-driven illusions. In this work, we compared the intensity of BOT illusion for operators in two conditions; motion-control and BCI-control. Our results revealed a significantly stronger BOT illusion for the case of BCI-control. This finding highlights BCI's potential in inducing stronger agency-driven illusions by building a direct communication between the brain and controlled body, and therefore removing awareness from the subject's own body.

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Figures

Figure 1
Figure 1. Body ownership transfer (BOT) during teleoperation of a humanlike robot.
(a) The cognitive model of body recognition suggests that when operators control the robot’s body, the match between the sensory prediction of motor intentions and the sensory feedbacks (the visual feedback from the robot’s body in the head-mounted display and the proprioceptive feedback from the operator’s body) yields an illusion that the robot’s body belongs to the operator (BOT). To investigate the effect of proprioceptive feedback, subjects controlled the robot’s hands using two interfaces; (b) a motion-capture system that copied the operator’s grasp to the robot’s hands (with proprioception) and (c) a BCI system that translated the subjects’ EEG patterns of motor imagery to robot’s hand motions (without proprioception). In both sessions, skin conductance response (SCR) and EMG signals were recorded and monitored.
Figure 2
Figure 2
Evaluation results for questionnaire, SCR, EMG and post-experimental interview (a) The intensity of BOT illusion was mainly evaluated by measuring subjects’ reaction to a painful stimulus (injection) applied to the robot’s hand at the end of each session. (b) EMG electrodes were attached to both left and right arms with the ground and reference electrodes attached to the wrist bones. SCR electrodes were attached to the left palm. (c) Subjects scored Q1~Q9 in each BCI and MoCap session based on a 7-point Likert scale, 1 denoting “didn’t feel at all” and 7 denoting “felt very strongly”. Mean values, standard deviations and p-values (Wilcoxon Signed-Rank test) of the obtained scores are shown on the graph. Statistical significance was found in Q1, Q2, Q3 and Q5 showing an overall higher BOT illusion in the BCI session. (d) SCR peak value, measured immediately after the injection, was assigned as the reaction value. Mean reaction values and standard deviations are plotted. BCI responses revealed a significantly higher reaction to the injection. (e) The mean EMG activity measured from the subjects’ arms in each session was averaged per condition and compared to the EMG values in the Rest phase. Results confirmed the absence of movement and unconscious muscle contractions during the BCI session. (f) In the post-experimental interview, subjects were asked three questions in which they voted for the session with stronger sensation of injection (Q1), level of ownership (Q2) and task feasibility (Q3). Although MoCap was significantly selected as the easier session, BCI was chosen as the session with higher sensation of injection and ownership.
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