Revisiting the Rubber Hand Illusion: Exploring Feelings of Ownership Towards a Digital Hand
The mechanisms behind the cognitive processes relating to our sense of body ownership and self-attribution are still not fully understood. This study reproduces and builds upon the Rubber Hand Illusion (RHI), where subjects report the curious sensation of feeling an artificial hand as being their own. Two experiments are conducted. The first investigates if the results of the original RHI can be successfully reproduced using the same experimental design. The second investigates the constraints of the phenomenon using a virtual hand with a resolution of 55%, whilst applying a delay of 300ms. The results support the findings of the original RHI. Subjects in the experimental group exhibited a noticeable drift of 40mm toward the rubber hand, when asked to point to their own left hand; p = .007 and statements regarding ownership of the rubber hand proved significant; p < 0.05. A delay of 300ms in haptic feedback was sufficient to break the illusion in the second experiment, where there was a noticeable drift of-10mm away from the virtual hand for the control group, compared to a 29mm drift toward the virtual hand for the experimental group; p < .001. In addition, an anatomically correct virtual hand with a resolution of 55% was sufficient to create the illusion. In the experimental group 8 out 15 subjects, and 9 out 15 (60%) subjects in the control group felt that the virtual hand was their own, suggesting avatar bodily representations that are anatomically correct/similar elicit a sense of ownership.
During both experiments subjects sat upright, in front of a table, with a tape measure affixed to the nearside edge. The drift measures were recorded using the affixed tape measure before a condition was applied. During the condition subjects observed a ‘false’ hand located in front of them for a period of five minutes, while their own ‘real’ left hand which was situated pronated REVISITING THE RUBBER HAND ILLUSION | PAGE 3 (palm face down) on the table and hidden from view. During this period, the subject’s real hand was stoked with a paintbrush, at the same time as they observed the false hand being stroked with an identical paintbrush - either synchronously or asynchronously depending on the chosen condition. After five minutes had elapsed the drift measures were recorded once more, before subjects answered open questions about their experience. Lastly subjects completed a questionnaire. Two experiments were conducted.
The rubber hand illusion (RHI) is a body ownership illusion whereby congruently stroking a fake rubber hand and a subject's hidden hand while observing the rubber hand produces the illusion of them feeling the touch on the rubber hand and experiencing the rubber hand to be part of their own body. The parameters of the RHI have not been fully defined and we describe an approach utilising digital media and technology to examine and establish parameters for this illusion beginning with three experiments: (i) Repeating the original RHI to determine if our test conditions are conducive to producing the classic illusion. (ii) Replacing the original rubber hand with either a static or animated digital image of it displayed on a tablet. (iii) A VR implementation whereby participants see an image of their own hand viewed through a head-mounted display. Measurements of proprioceptive drift (an objective indicator of the feeling of ownership of the rubber hand) corroborated the original RHI and also suggested that a similar phenomenon can occur when the rubber hand was replaced with either a static or animated digital image of it or in a VR condition. Rubber hand illusion, digital media, virtual reality, body ownership illusions.