Perceived location and ownership of the hands

Abstract

Proprioception, the perception of our own body, is crucial for interacting with our surroundings. This thesis focuses on two components of proprioception in healthy participants: perceived location and the perceived ownership of the hands. Experiments inducing illusions of body ownership lead participants to perceive an artificial object, such as a rubber hand, belongs to them. This is accompanied by errors in perceived location of their real hand. This thesis presents findings from two studies. The first study investigated whether the grasp illusion— an illusory coming together of the hands and a sense of body ownership induced by passively grasping a rubber finger— is present with the hands separated horizontally. The participant’s right index finger was passively grasped at the body midline while they passively grasped a rubber finger with their left thumb and index for 3 min. Five positions across the horizontal workspace were tested. On average, participants did not exhibit a body ownership illusion at any position. However, passively grasping the rubber finger led to smaller perceived spacing between hands when they were moderately crossed (3.2 cm [0.7 to 5.7]) (mean [95% CI]). The second study investigated how participants perceive the location of their unseen hand immediately after it is passively placed at different positions across the horizontal workspace, with and without their other hand in the workspace. Participants perceived their hand closer to the body midline at all hand positions, particularly when the hand was placed in it’s own side of the workspace. Presence of the other hand had no effect on perceived hand location. In summary, this thesis reveals that healthy participants make systematic errors in perceived hand location in the absence of vision, and that these errors are not necessarily a result of body ownership illusions or time. These results are important to allow appropriate interpretation and understanding of proprioception and motor control studies in both healthy and clinical populations.