The extreme flexibility of the body representation had been studied in the s by Lackner It was found that applying vibrations of around Hz to a muscle tendon on the biceps leads the forearm to move in flexion, but if the movement is resisted, then there will be an illusion of movement of the forearm in the opposite direction extension.
Now suppose that both hands are holding the waist and such muscle spindle vibrations are applied. There is an illusion that both arms are extending, but since the hands are attached to the waist this is impossible. The way that the brain resolves this is to give the illusion of an expanding waistline! By vibrating on the other side of the muscle tendons the arms can be given the illusion of flexing — which will result in a shrinking waist illusion.
Ehrsson et al. Tidoni et al. This followed earlier work by Leonardis et al. This was part of an Embodiment Station discussed in Section 6. Regarding non-human body configurations Ehrsson and Guterstam et al. Regarding body shape, Kilteni et al. This illusion had first been implemented and experienced at VPL in the s, although not published. Steptoe et al. Participants learned how to use the tail in order to avoid harm to the body. More recently, Won et al.
Some implications of this across a range of fields have been discussed in Won et al. Returning to the RHI, Ijsselsteijn et al. Although the subjective illusion was reported, the proprioceptive drift effect did not occur. Using VR, Slater et al.
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This was achieved by a virtual arm being displayed on a powerwall as projecting in stereo out of the real shoulders of participants. This was done synchronously in which case the full illusion of ownership occurred including proprioceptive drift, or asynchronously, which typically did not result in the illusion. In the full body illusion setup of Petkova and Ehrsson , there was no head tracking so that participants had to be looking down in a fixed orientation toward their body, in order to see the manikin body as substituting their real body.
Slater et al. We refer to this as first-person perspective 1PP. The experiment also included visuotactile synchrony they felt their arm being stroked in synchrony with seeing their corresponding virtual arm stroked or visuotactile asynchrony. There was also a condition where the virtual body was seen from a third-person perspective 3PP i. In this setup, it was found that 1PP was clearly the dominant factor, although visuotactile synchrony had some contribution. Remarkably, the illusion occurred in spite of the fact that all the participants were adult males but were embodied in a young female body.
The vital importance of 1PP for body ownership was also emphasized by Petkova et al. One of the major advantages of VR in this context compared to using rubber hands or manikin bodies is that virtual limbs or the whole virtual body can be moved. Sanchez-Vives et al. Participants wearing a data glove that tracked the movements of their hand and fingers saw a virtual hand projected in stereo 3D on a powerwall move in synchrony or asynchrony with their real hand movements. This resulted in an illusion of ownership just as with visuotactile stimulation.
The same can be done for the body as a whole. Through real-time motion capture, mapped onto the virtual body, when the person moves their real body they would see the virtual body move correspondingly. Participants can see their virtual body moving by directly looking toward themselves and in virtual mirror reflections and shadows Slater et al.
Kokkinara and Slater showed in later work that when there is a 1PP view of the virtual body then visuomotor synchrony is the more powerful inducer of the body ownership illusion than visuotactile synchrony. This requires the stereo HMD with wide field-of-view so that the person can actually see their virtual body , with head tracking, at the minimum. Additional multisensory correlations such as visuotactile and visuomotor synchrony may be included. A technical setup to achieve this is described in Spanlang et al. There has been a lot of work on building virtual embodiment technology Spanlang et al.
There have also been studies on how illusions of body ownership might result in various changes to the real body. For example, it had previously been shown that the RHI leads to a cooling of the real hand Moseley et al. Cooling of several points on the body has also been reported in a 3PP full body illusion Salomon et al. There is also evidence using VR suggesting that the 1PP full body ownership illusion can result in changes in temperature sensitivity Llobera et al. Banakou and Slater showed that embodiment in a virtual body that is perceived from 1PP and that moves synchronously with the real body can result in illusory agency over an act of speaking.
The virtual body was seen directly and in a virtual mirror. Participants spent a few minutes simply moving with the virtual body moving synchronously with their movements in the experimental condition or asynchronously in another. At some moment, the virtual body unexpectedly uttered some words 45 in total with appropriate lip sync.
Those in the visuomotor synchronous condition later reported a subjective illusion of agency over the speaking — as if they had been the ones who had been speaking rather than only the virtual body.
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Moreover, when participants were asked to speak after this exposure, the fundamental frequency of their own voice shifted toward that of the higher frequency voice of the virtual body. Thus embodiment resulted in the preparation of a new motor plan for speaking, which was exhibited by participants in the synchronous condition changing the way that they spoke after compared to before the experiment.
This did not happen for those in the asynchronous condition. Thus, VR offers a very powerful tool for the neuroscience of body representation. For a recent review of this field, see Blanke et al. In the next section, we consider some of the consequences of changing representations of the self.
Oftentimes, being able to change your own definition is actually part of a practical application. This quote is another illustration that much of what is being discussed today was already thought of and even implemented in the heady days of early VR. If VR can endow someone with a different body, what consequences does this have? We have already mentioned above that ownership over a rubber hand can lead to physiological responses, and there is some evidence that points to the possibility that the experimental real arm can experience very small drops in temperature, and that the same can occur over different parts of the body in a virtual whole body illusion, or that in the virtual arm illusion that there may be a change in temperature sensitivity.
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But, are there higher-level changes to attitudes, behaviors, even cognition? Essentially, the personality or type of body or the actions associated with the digital representation would influence the actual real-time behaviors of participant, both in the VR and later outside it. In their paper, they showed that being embodied in an avatar that had a face that was judged as more attractive than their actual one led participants to move closer to someone else displayed in a collaborative virtual environment than those participants whose avatar face was judged less attractive.
Similarly, being embodied in taller avatars led to more aggressive behaviors in a negotiation task than being embodied in shorter avatars. These results also carried over to representations in online communities Yee et al. Groom et al. The embodiment was through an HMD with head tracking, with the body seen in a mirror, and lasted for just over 1 min. This difference did not occur when participants simply imagined being in a White or Black body.
Hershfield et al. They embodied people in a virtual body that either had a representation of their own faces, or their faces aged by about 20 years. The virtual body was shown in a virtual mirror. They found some modest evidence in favor of the hypothesis that being confronted with their future selves influenced their behavior toward greater savings for the future. See also the example concerned with fostering exercise Fox and Bailenson, in Section 3. It has been also been argued that attitudinal and behavioral correlates of transformed body ownership can be explained as people behaving according to how others would expect someone with that type of body to behave Yee and Bailenson, Essentially, this comes down to stereotyping.
For example, in the case of the racial bias study of Groom et al. In an experiment by Kilteni et al. The body moved with visuomotor synchrony, but also there was synchronous visuotactile feedback through a drumming task, so that participants saw their virtual hands hit a virtual hand drum that was coincident in space with a real hand drum.
Hence, when they hit the virtual drum they would also feel it. This result occurred, in the view of the stereotype theory, because there is greater expectation that people who look more like Jimi Hendrix would be more bodily expressive. However, self-perception theory and stereotyping cannot account for attitudinal changes that have been observed in experiments where only the body changes, and there are no particular behavioral demands within the study.
These results are better explained within the multisensory perception framework based on the research that has stemmed from the RHI.
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Peck et al. The body moved synchronously with real body movements of the participants through real-time motion capture and was seen directly by looking toward the self with the head-tracked HMD and in a mirror. A racial IAT was applied some days before the experience and then immediately after. It was found that average implicit racial bias significantly decreased only for those who had the Black embodiment. During the 12 min of exposure, the participant did not have any task except to move and to look toward themselves and in the mirror while doing so. The only events that occurred were that 12 virtual characters walked by, 6 of them Black and the others White.
It is likely that the results are different from Groom et al. Given the contrary earlier result of Groom et al. However, independently it was shown by Maister et al. For a review of this area of research see Maister et al. Recent results demonstrate that the decrease in implicit bias lasts for at least 1 week after the exposure Banakou et al. Banakou et al. However, if the form of the body represented that of a 4-year-old child then the size overestimation was approximately double that compared to when the form of the body was an adult body but shrunk down to the same size as the child.
Moreover, in the child embodiment case, there were changes in implicit attitudes about the self toward being child-like substantially beyond changes induced by the illusion of ownership of the adult-shaped body of the same size. In other words, only the form of the body child-like compared to adult-like has this effect.
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