Worth a Thousand Words

This week’s image is not from this world. It is from a virtual world. What you think you see in this picture looks like a woman slapping another woman on the face. But that is an illusion – the slap is delivered by the experimenter, and the recepient of the slap is an avatar of a male participant in the study. What is truly novel about the experiment is that the participants exhibited physiological responses to seeing their virtual avatar slapped on the computer screen, just as if they were physically slapped in the face in the Real Life. While similar results were found in individual body part, e.g., the famous “rubber hand” experiment, this is the first case of a whole-body transfer and the first one in a virtual environment. The technique has obvious potential in study of a variety of sensory and neurological aspects of the human brain as well as potential for treatment of disorders ranging from ‘phantom limb’ to PTSD.

The image comes from the PLoS ONE article: First Person Experience of Body Transfer in Virtual Reality by Mel Slater, Bernhard Spanlang, Maria V. Sanchez-Vives and Olaf Blanke.

From the Abstract:

Background

Altering the normal association between touch and its visual correlate can result in the illusory perception of a fake limb as part of our own body. Thus, when touch is seen to be applied to a rubber hand while felt synchronously on the corresponding hidden real hand, an illusion of ownership of the rubber hand usually occurs. The illusion has also been demonstrated using visuomotor correlation between the movements of the hidden real hand and the seen fake hand. This type of paradigm has been used with respect to the whole body generating out-of-the-body and body substitution illusions. However, such studies have only ever manipulated a single factor and although they used a form of virtual reality have not exploited the power of immersive virtual reality (IVR) to produce radical transformations in body ownership.

Principal Findings

Here we show that a first person perspective of a life-sized virtual human female body that appears to substitute the male subjects’ own bodies was sufficient to generate a body transfer illusion. This was demonstrated subjectively by questionnaire and physiologically through heart-rate deceleration in response to a threat to the virtual body. This finding is in contrast to earlier experimental studies that assume visuotactile synchrony to be the critical contributory factor in ownership illusions. Our finding was possible because IVR allowed us to use a novel experimental design for this type of problem with three independent binary factors: (i) perspective position (first or third), (ii) synchronous or asynchronous mirror reflections and (iii) synchrony or asynchrony between felt and seen touch.

Conclusions

The results support the notion that bottom-up perceptual mechanisms can temporarily override top down knowledge resulting in a radical illusion of transfer of body ownership. The research also illustrates immersive virtual reality as a powerful tool in the study of body representation and experience, since it supports experimental manipulations that would otherwise be infeasible, with the technology being mature enough to represent human bodies and their motion.

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2 Responses to Worth a Thousand Words

  1. melslater says:

    Hi, I just want to correct something – no one was slapped.
    Participants in the experiment saw the slap from an elevated position as shown in the picture, but there was no physical contact corresponding to the slap that they saw.

    Those subjects who had earlier seen the world through the eyes of the virtual seated girl tended to have a greater heart rate response in relation to the slap than those who had earlier seen the world through the perspective position that was near to the girl but not co-located with her.

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  2. You are correct. The slap, like everything else in the experiment was – virtual ;-)

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