Reflections on the Hand: The Use of a Mirror Highlights the Contributions of Interpreted and Retinotopic Representations in the Rubber-Hand Illusion

Abstract

In the rubber-hand illusion, observing a rubber hand stroked in synchrony with one's own hand results in mislocalisation of the own hand, which is perceived as being located closer to the rubber hand. This illusion depends on having the rubber hand placed at a plausible egocentric orientation with respect to the observer. In the present study, we took advantage of this finding in order to compare the relative influence on the illusion of the rubber hand's perceived retinotopic image against its real-world position. The rubber hand was positioned egocentrically (fingers away from the participant) or allocentrically (fingers towards the participant), while participants viewed it either directly or via a mirror that was placed facing the participant. In the mirror conditions, the orientation of the retinotopic image of the hand (either egocentric or allocentric) was opposed to its real-world orientation. We found that the illusion was elicited in both mirror conditions, to roughly the same extent. Thus either of two representations can elicit the rubber-hand illusion: a world-centred understanding of the scene, resulting from the inferred position of the hand based on its mirror reflection, or a purely visual retinotopic representation of the viewed hand. In the mirror conditions, the illusion was somewhat weaker than in the typical directly viewed egocentric condition. We attribute this to competition between two incompatible representations introduced by the presence of the mirror. Finally, in two control experiments we ruled out that this reduction was due to two properties of mirror reflections: the increased perceived distance of items and the reversal of the apparent handedness of the rubber hand.

Self-body recognition through a mirror: Easing spatial-consistency requirements for rubber hand illusion

“…The rubber hand illusion (RHI) is an illusory experience of body ownership of a fake study supports this possibility; in it, the body ownership illusion was evoked 23 irrespective of the egocentric or allocentric fake hand images in a mirror [11]. The 24 present study pursues these hypothetical propositions.…”

“…29 Experiment 2 investigates whether the incongruency of the fake and actual hands' 30 postures (angles) is accepted in the RHI setting involving a mirror. Although Kontaris 31 and Downing [11] found that first-person and third-person perspective images of a fake 32 hand in a mirror did not differ in terms of the subjective experience of the 33 body-ownership illusion, they did not deal with situations where the actual and fake 34 hands were angled. Exp.…”

“…The weightings of sensory cues would 258 be different between conditions with and without a mirror. Such an effect of less 259 reliable images in a mirror was pointed out in [11], in which even laterality was 260 masked by using mirror images of a fake hand. In other words, in classical RHI 261 settings where the fake hand is gazed at directly, because of the greater contribution of 262 visual cues, visible incongruency may cause the visual sense to fail to capture other 263 cues and prevent the occurrence of the illusion.…”

“…25 In Experiment 1, we test whether the body ownership illusion is elicited when 26 experimental participants gaze at the mirror image of a fake hand. This experiment is 27 not merely a replication of earlier ones [10,11] as we tested that our settings involving 28 self-generated hand motions and tactile stimuli cause the illusory experiences. 29 Experiment 2 investigates whether the incongruency of the fake and actual hands' 30 postures (angles) is accepted in the RHI setting involving a mirror.…”

“…and Preston [12], which investigated the mirror RHI. Other related studies have 221 reported body ownership through a mirror at the same extent [10] or weaker [11] as 222 compared to the condition without a mirror. However, these studies investigated 223 passive RHI, in which the experimental conditions differed from our study and that of 224 study of Jenkinson and Preston [12] in terms of involvements of hand movements.…”