Body swap illusion made friends feel alike

Swedish neuroscientists have found that the sensation of the body is closely related to the self-perception of the individual, and if it is illusory to swap two friends' bodies, they will perceive their character more like the other. In addition, the inconsistency between the perception of body and personality in such an illusion impairs episodic memory. The article was published in the iScience journal.

An important part of self-perception is the feeling of one's own body: a person feels that the body belongs to him and that in it he seems to be fenced off from the world around him. However, in some mental disorders (for example, schizophrenia and depression), the sense of the body is blurred, and at the same time the self-perception of the individual changes as well.

Such disturbances in perception can be simulated using illusions. So, according to the principle of the illusion of a rubber hand (when an artificial hand is placed next to a real one, the latter is covered with a screen and both are touched at the same time), one can make a person feel that another body belongs to him. The fact that a person is connected with himself is remembered better, but it is not known how much bodily illusions change a person's idea of ​​his personality and affect memory.

Scientists from the Swedish Karolinska Institute, led by Pawel Tacikowski, created the illusion of a body change in 66 couples of friends. The participants lay down on couches, cameras were installed over their heads: the view they filmed was similar to that of a person lying in front of them. The image was broadcast to virtual reality glasses, and the participants saw either their own body or the body of a friend lying next to them as their own.

There were two experimenters nearby and at certain moments simultaneously or with a delay of three seconds touched the same part of the body of both friends. Thus, the participants saw how the body, which is located in the place where their own body should be, was touched - and felt a similar touch. Then the experimenters put a knife to the body, which the volunteers saw with glasses. So the researchers tested whether the illusion worked - if the participants perceived the visible body as their own, the appearance of the knife scared them and the conductivity of the skin increased.

Experiment design and four experimental conditions / Pawel Tacikowski, Marieke Weijs & Henrik Ehrsson / iScience, 2020Share this

Before the start of the experiment, each of the volunteers answered 120 questions about their friend (assessed how different personality traits fit his character). During the illusion, the participants were asked the same questions, but about themselves, 30 in each of the four conditions (when they saw their own or someone else's body, and the visible touches coincided with the felt ones or not) - the scientists evaluated how the self-perception of the personality differs if a person feels yourself in the body of another.

After each of the four stages of the experiment, participants rated the fidelity of several statements about the power of the illusion (for example, “I felt that the body I saw belonged to me”). Finally, after the experiment, the scientists assessed the episodic memory of the participants: they named the same 120 personality traits and 120 new ones and asked them to remember which of them had already been met. The illusion really worked: the majority of the volunteers answered yes to the questionnaire; the scores were significantly higher, and reactions to the knife were stronger when the bodies of friends were touched simultaneously (p <0.005). During the full-fledged body-swapping illusion, personality self-perception was closer to assessing the friend's character than when the illusion was incomplete or the participants were looking at their own body (p <0.05). That is, the participants perceived their character in the same way as the character of a friend, if they felt a movement into his body. Moreover, the more the volunteers felt their friend's body as their own, the more similar were the personality assessments (p <0.05).

On the horizontal axis: the difference in skin conductance in the illusion with synchronous and asynchronous touching of a friend's body. On the vertical axis: the difference in the similarity of the personal assessment of oneself and a friend under the same two conditions / Pawel Tacikowski, Marieke Weijs & Henrik Ehrsson / iScience, 2020Share this

On the memory test, participants remembered less well the traits they were asked about during the full illusion. Scientists explained such a violation of episodic memory by the fact that the illusion created a conflict between the bodily and general perception of oneself, the consistency of the concept of "I" was violated, and as a result, the memory of the events associated with the subject suffered. However, in volunteers whose personality scores of themselves and a friend were similar, the test result for episodic memory was higher (p = 0.029), and the traits that were asked about in different conditions were remembered in the same way - probably, in this case, the discrepancy between the self-perception of body and personality was less.

Episodic memory test results under four conditions (red - full-fledged illusion) in participants whose self-perception of personality changed strongly or weakly during the illusion/ Pawel Tacikowski, Marieke Weijs & Henrik Ehrsson / iScience, 2020Share this

The authors of the work concluded that the image of one's own body dynamically affects the self-perception of an individual, and the consistency between these two concepts is important for the normal functioning of episodic memory. The results of the work will help to understand personality disorders that arise in schizophrenia and depression.

The prototype of the illusion of body exchange - the rubber hand illusion - works with a variety of objects. The classic application of this method is to help people get used to dentures, but you can even feel the phone as part of your own body. The illusion also works in macaques, and experiments like this help neuroscientists map the body representation in the brain of animals.

Tags: #Psychology #Neurosciences #Science

Photo: Pawel Tacikowski, Marieke Weijs & Henrik Ehrsson / iScience, 2020

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