Ownership and Agency of an Independent Supernumerary Hand Induced by an Imitation Brain-Computer Interface

TL;DR

This study demonstrates that individuals can feel ownership and control over a virtual supernumerary hand through an imitation brain-computer interface, even without a causal link between brain activity and hand movement.

Contribution

It introduces a novel illusion showing independent ownership and control of a third hand without affecting real hand ownership, expanding understanding of body ownership illusions.

Findings

Subjects felt ownership over the third hand despite no causal link.

Ownership of real hands was maintained during the illusion.

The illusion was achieved with 80% correct virtual hand movements.

Abstract

To study body ownership and control, illusions that elicit these feelings in non-body objects are widely used. Classically introduced with the Rubber Hand Illusion, these illusions have been replicated more recently in virtual reality and by using brain-computer interfaces. Traditionally these illusions investigate the replacement of a body part by an artificial counterpart, however as brain-computer interface research develops it offers us the possibility to explore the case where non-body objects are controlled in addition to movements of our own limbs. Therefore we propose a new illusion designed to test the feeling of ownership and control of an independent supernumerary hand. Subjects are under the impression they control a virtual reality hand via a brain-computer interface, but in reality there is no causal connection between brain activity and virtual hand movement but correct movements are observed with 80% probability. These imitation brain-computer interface trials are interspersed with movements in both the subjects' real hands, which are in view throughout the experiment. We show that subjects develop strong feelings of ownership and control over the third hand, despite only receiving visual feedback with no causal link to the actual brain signals. Our illusion is crucially different from previously reported studies as we demonstrate independent ownership and control of the third hand without loss of ownership in the real hands.