Virtual skirt and legs turn men into girls

Video: Body transfer illusion

Last time you checked you were a conservatively dressed, 28-year-old man. But you look down and notice that you now have the legs of a 10-year-old girl and appear to be wearing a skirt.

It turns out that this experience – facilitated by a virtual-reality headset and some brief arm-stroking – is enough to make men in their mid-20s react as if this new body is their own. They feel that way even when they subsequently move outside the girl's perspective and watch her being attacked.

"This is the first experiment to show that body ownership can be transferred to an entirely virtual body," says Mel Slater of the University of Barcelona, Spain, who led the team that carried out the experiment.

The finding highlights how far our sense of self and body image can be manipulated, and could lead to therapies for conditions of body-image distortion such as anorexia.

Rubber hands

Over 10 years ago, body-transfer illusions were first demonstrated using a false hand. In the so-called rubber hand illusion, researchers found that if they put a rubber hand on a table in front of a person, and then stroked the rubber hand and the person's own hand at the same time and in the same way, they could convince the volunteer that the rubber hand was their own.

More recently, the illusion was replicated using full-body manikins: volunteers' skin conducted more electricity when their manikin double was attacked with a knife, indicating fear.

To see if the virtual world could be used to induce a similar illusion, Slater's team gave 24 men a head-tracking video display to wear and recorded their heart rates. When the volunteers looked down, in place of their own body they saw that of a 10-year-old girl in a tartan skirt. They also saw a virtual woman approaching them and stroking their virtual girl's arm, while in the real world unseen experimenters touched the men's flesh-and-blood arm.

After this preparation, the virtual visual angle of the men's headsets changed, and the volunteers found themselves looking down on their avatars. They now saw the girl being slapped by the virtual woman. Immediately afterwards, the men were asked to rate how strongly they felt that the girl's body was theirs.

Pounding heart

On average, the men reported medium-strength feelings about the girl's body being their own, and strong feelings that the woman was touching their body.

Stranger still, as the girl was slapped, the men's heart rate changed in ways that were similar to, although not as great as, those recorded when people feel threatened. Slater emphasises that this was surprising, given that the men were looking down on the girl, from a third-person perspective, by this point.

These changes in heart rate did not occur when the same men did a second experiment that was identical, except they viewed the whole scene from the third-person point of view.

The experiment demonstrates the strong connection the volunteers felt to their new, virtual bodies, says Slater. He suggests that the familiarity of looking down and seeing our own body "is so overwhelming" that even dramatic changes in body won't override the influence of vision.

Malleable self

The findings might be applied to entertainment – to make video games more immersive, for example – but also to psychology. People considering a sex change have used the virtual world of Second Life to test what it is like to have a different gender.

Meanwhile, previous studies found that giving people virtual-reality avatars that are taller or shorter than they are alters the way they behave. Making ourselves fatter or slimmer could also have "profound implications" on our psychology and behaviour, says Slater, which could be used to develop therapies for people with body-image problems.

Alexander Mussap of Deakin University in Melbourne, Australia, who has studied the rubber hand illusion in the context of eating disorders, says the new research further demonstrates that "our sense of self is surprisingly malleable".

Social neuroscientist Liane Young at the Massachusetts Institute of Technology says that knowing that people transfer themselves into avatars could be used to answer many questions in psychology.

Journal reference: PloS One, DOI: 10.1371/journal.pone.0010564

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