Humanlike robot hands controlled by brain activity arouse illusion of ownership in operators

Abstract

Operators of a pair of robotic hands report ownership for those hands when they hold image of a grasp motion and watch the robot perform it. We present a novel body ownership illusion that is induced by merely watching and controlling robot's motions through a brain machine interface. In past studies, body ownership illusions were induced by correlation of such sensory inputs as vision, touch and proprioception. However, in the presented illusion none of the mentioned sensations are integrated except vision. Our results show that during BMI-operation of robotic hands, the interaction between motor commands and visual feedback of the intended motions is adequate to incorporate the non-body limbs into one's own body. Our discussion focuses on the role of proprioceptive information in the mechanism of agency-driven illusions. We believe that our findings will contribute to improvement of tele-presence systems in which operators incorporate BMI-operated robots into their body representations.

Figure 1. Experiment setup.

EEG electrodes placed on subject's sensorimotor cortex recorded brain activities during motor imagery tasks. Subjects wore a head mounted display through which they had a first person view of the robot's hands. They received cues by lighting balls in front of the robot's hands and held grasp images for their own corresponding hands. Classifier detected two classes of results (right or left) and sent a motion command to robot's hand. SCR electrodes, attached to subject's left hands, measured physiological arousal during the session. Identical blankets were laid on both robot and subject legs so the background views were the same.

Figure 2. Participant's view in HMD.

(a) Robot's right hand grasped lighted ball based on classification results of subject's EEG patterns. (b) Robot's left hand received injection at the end of each test session, and subject reactions were subjectively and physiologically evaluated.

Figure 3. Evaluation results.

(a) Participants answered Q1 and Q2 immediately after watching injections. Q1) When robot's hand was given a shot, did it feel as if your own hand was being injected? Q2) Throughout the session while you were performing the task, did it feel as if the robot's hands were your own hands? Mean score values and standard deviations for each condition were plotted. Significant difference between conditions (**p < 0.001; paired t-test) was confirmed. (b) SCR peak value after injection was assigned as reaction value. Mean reaction values and standard deviations were plotted, and results show significant differences between conditions (*p < 0.01; paired t-test).

Figure 4. Body recognition mechanism.

Explanation of mechanism of body ownership illusion to an operated robotic body is based on Tsakiris cognitive model for self-recognition. During tele-operation of a very human-like android, match between efferent signals of a motor intention and afferent feedback of the performed motion (proprioceptive feedback from operator's body and visual feedback from robot's body) yields illusion that robot's body belongs to the operator. However, the role of proprioceptive feedback in modulation of such feelings has never been completely clarified. This work confirms that the body ownership illusion was elicited without proprioceptive feedback and by modulation of only motor commands and visual inputs.