Individual Differences in the Rubber Hand Illusion Are Related to Sensory Suggestibility

Abstract

In the rubber hand illusion (RHI), watching a rubber hand being stroked in synchrony with one’s own hidden hand may induce a sense of ownership over the rubber hand. The illusion relies on bottom-up multisensory integration of visual, tactile, and proprioceptive information, and on top-down processes through which the rubber hand is incorporated into pre-existing representations of the body. Although the degree of illusory experience varies largely across individuals, the factors influencing individual differences are unknown. We investigated whether sensory suggestibility might modulate susceptibility to the RHI. Sensory suggestibility is a personality trait related to how individuals react to sensory information. Because of its sensory nature, this trait could be relevant for studies using the RHI paradigm. Seventy healthy volunteers were classified by Sensory Suggestibility Scale (SSS) scores as having high or low suggestibility and assigned to either a high- (High-SSS) or a low-suggestibility (Low-SSS) group. Two components of the RHI were evaluated in synchronous and asynchronous stroking conditions: subjective experience of sense of ownership over the rubber hand via a 9-statement questionnaire, and proprioceptive drift as measured with a ruler. The High-SSS group was generally more susceptible to the subjective component; in the synchronous condition, they rated the statement assessing the sense of ownership higher than the Low-SSS group. The scores for this statement significantly correlated with the total SSS score, indicating that the higher the sensory suggestibility, the stronger the sense of ownership. No effect of sensory suggestibility on proprioceptive drift was observed, suggesting that the effect is specific for the subjective feeling of ownership. This study demonstrates that sensory suggestibility may contribute to participants’ experience of the illusion and should be considered when using the RHI paradigm.

Illusory hand ownership in a patient with personal neglect for the upper limb, but no somatoparaphenia

“…It seems that, when PN was absent, our patient was not susceptible to experience the illusion of fake hand ownership. A failure in experiencing the RHI is not by itself a sign of a defective body representation, and the lack of the illusion is in line with the literature showing individual differences in the subjective feeling of ownership induced by the RHI (Haans, Kaiser, Bouwhuis, & IJsselsteijn, 2012;Marotta, Tinazzi, Cavedini, Zampini, & Fiorio, 2016). Therefore, in the absence of a pathological bodily condition (i.e., PN), the patient correctly integrated visual and tactile information delivered between his own and a fake hand, but this multisensory integration did not lead to an alteration of the subjective sense of hand ownership for both the right (first and second sessions) and the left (second session) hands.…”

A Protective Mechanism against Illusory Perceptions Is Amygdala-Dependent

“…Furthermore, we have previously shown that intranasal OXT modulates the processing of affective touch in a context-dependent manner rather than altering touch perception per se (Scheele et al, 2014;Kreuder et al, 2017). Thus, our data suggest that the amygdala may play an important role in multisensory integration of temporally congruent tactile, visual, and proprioceptive information (i.e., bottom-up processes in the RHI) or may be involved in the integration of external stimuli into one's own body representation (i.e., top-down processes in the RHI; Marotta et al, 2016). Importantly, the observation that a complete absence of the RHI in a subsample of five participants was not associated with significantly larger amygdala volumes underscores the importance of multisensory integration in other brain areas like the premotor cortex (Ehrsson et al, 2004) or the temporoparietal junction (Olivé et al, 2015).…”

“…"), and ownership feelings toward the rubber hand (Item 3: "I felt as if the rubber hand were my hand."). Item 3 has been found to be particularly informative to quantify susceptibility for body ownership illusions, whereas Items 1 and 2 are instead closely related to touch localization (Marotta et al, 2016). We thus operationalized "illusion vividness" as the mean response to RHIQ items 1-3 (for a similar approach, see Morgan et al, 2011), whereas the single response to Item 3 was defined as "body ownership experience".…”

“…or "The rubber hand began to resemble my own (real) hand, in terms of shape, skin tone, freckles or some other visual feature."]. In case of a successful illusion induction, participants are expected to report high agreement with the target items, Items 1-3, while scoring much lower on the control items, Items 4 -9 (Marotta et al, 2016). Because it is still elusive how subjects without illusory experience in the RHI differ from subjects with illusion experience, data from subjects reporting no illusion experience in either run of the experiment (N ϭ 5 in Experiment 1, N ϭ 5 in Experiment 2) were discarded from the final dataset.…”

Can Wearable Haptic Devices Foster the Embodiment of Virtual Limbs?

“…The experimental results imply that haptic feedback devices can alter human body experience and foster the subjective embodiment of non-corporal limb avatars. Even though the experience of bodily illusions can vary largely across individuals [55], the exertion of tactile feedback yielded significantly increased subjective embodiment. In particular, the embodiment questionnaire by Longo [18] indicates that certain experiences of ownership were additionally increased if force feedback was provided.…”