Illusory ownership of a virtual child body causes overestimation of object sizes and implicit attitude changes

Abstract

An illusory sensation of ownership over a surrogate limb or whole body can be induced through specific forms of multisensory stimulation, such as synchronous visuotactile tapping on the hidden real and visible rubber hand in the rubber hand illusion. Such methods have been used to induce ownership over a manikin and a virtual body that substitute the real body, as seen from first-person perspective, through a head-mounted display. However, the perceptual and behavioral consequences of such transformed body ownership have hardly been explored. In Exp. 1, immersive virtual reality was used to embody 30 adults as a 4-y-old child (condition C), and as an adult body scaled to the same height as the child (condition A), experienced from the first-person perspective, and with virtual and real body movements synchronized. The result was a strong body-ownership illusion equally for C and A. Moreover there was an overestimation of the sizes of objects compared with a nonembodied baseline, which was significantly greater for C compared with A. An implicit association test showed that C resulted in significantly faster reaction times for the classification of self with child-like compared with adult-like attributes. Exp. 2 with an additional 16 participants extinguished the ownership illusion by using visuomotor asynchrony, with all else equal. The size-estimation and implicit association test differences between C and A were also extinguished. We conclude that there are perceptual and probably behavioral correlates of body-ownership illusions that occur as a function of the type of body in which embodiment occurs.

Keywords: body awareness; perceptual illusion; self consciousness.

Fig. 1.

Experimental setup. The body of the participant was substituted by a sex-matched virtual body, viewed from first-person perspective, onto which body and head movements were mapped in real time. The body could also be seen as reflected in a virtual mirror as shown. The body each participant viewed depended on the condition C (for child) or A (for adult) to which each one was assigned. (A) A female participant in a child’s body. (B) A female participant in a scaled-down adult’s body. (C) Participants’ body movements were tracked by 34 Optitrack markers.

Fig. 2.

Box and bar plots of questionnaire, size estimations, and IAT results by the Adult and Child conditions for Exps. 1 and 2. (A and B) Box plots for questionnaire results on body ownership (see Table S2) for Exps. 1 and 2, respectively. The thicker horizontal lines are the medians and the boxes the interquartile ranges. (C and D) Bar chart size-estimation results for Exps. 1 and 2. The heights are means and the bars SEMs. The variable dmean15, dmean30, and dmean45 are the differences between the postembodiment size estimations and preembodiment (baseline) size estimations, for the boxes of the three different sizes. (E and F) Bar charts for the IAT results for Exps. 1 and 2. A higher IAT score represents faster response times for self compared with child categories. Significance levels are given in the text.