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The illusion of the rubber hand: a curious psychological effect

The illusion of the rubber hand: a curious psychological effect

September 28, 2022

The study of optical illusions It has been of great help to psychology for what they can reveal about perceptual processes. To give an example, understand how our brain works with respect to proprioception, has been very useful for patients who have suffered an amputation. Thanks to techniques such as the mirror box it is possible to reduce your phantom pain and improve your quality of life.

For several decades, science has been interested in these phenomena. And technological progress has allowed us to acquire new knowledge and better understand what happens in our brain. A group of psychologists from Pennsylvania (United States) discovered a curious illusion, known as "illusion of the rubber hand".

Researchers realized that if we put a rubber hand in front of us and, at the same time, we cover one of our arms so that it looks like the rubber hand is part of our body, when someone caresses our rubber hand , we will feel that we are caressing the real hand.

Below you can see how the illusion of the rubber hand happens:

The illusion of the rubber hand, more than a simple trick for illusionists

The illusion of the rubber hand not only became a trick for the illusionists, but it was an important finding because It allowed us to understand how sight, touch and proprioception (that is, the sense of the position of the body) are combined to create a convincing feeling of the property of the body, one of the foundations of self-consciousness.

The property of the body is a term that is used to describe the meaning of our physical self and differentiate it from the fact that it is not part of us. It is what allows us to know that a hammer we are holding with our hand is not part of our body or, in the case of animals, that they know that they should not eat their feet because they belong to their own body.

The discovery of the illusion of the rubber hand has inspired many researchers

For the neuropsychologist at the Karolinska Institute in Stockholm (Sweden), Henrik Ehrsson, "The illusion of the rubber hand has inspired many researchers, and many studies have tried to find the answers to this phenomenon. Science has wanted to know how the body is perceived by our mind, and how the integration of this information happens. "

Scientists have discovered that the greater intensity with which the illusion of the rubber hand is experienced, for example when hitting it hard, there is greater activity in the premotor cortex and parietal cortex of the brain. These areas are responsible for integrating sensory and movement information . But of course, it is not the same to caress the hand than to hit it. And despite the fact that individuals who have performed experiments with the rubber hand are aware that the hand is not part of their body, the brain regions that are activated by fear and threat, and that correspond to flight, as well they are activated more.

What happens to the authentic hand that is hidden?

Another interesting finding is that carried out by a group of scientists from the University of Oxford, who wanted to know what happens to the hand that hides during the experiment. If the brain reacts to the rubber hand, does it also react to the hand that is hidden? Well it seems that, just when the brain falsely recognizes the rubber hand as his, the temperature of the authentic hand, which is hidden, descends . In contrast, the rest of the body remains the same.

Furthermore, when the experimenter stimulates the hidden hand, the subject's brain takes longer to respond than when the other authentic hand is touched. These results seem to show that when the brain thinks that the rubber hand is an authentic hand, it forgets the other hand.

This has been really interesting for medicine because it shows that the body's thermal regulation also depends on the brain.

The mirror box therapy: another example of optical illusion

Illusion-based experiments have helped patients who have had amputations and who still feel pain despite the fact that the limb is no longer part of their body, which is known as "phantom pain".

The neurologist of CI enter the Brain and Cognition from the University of California at San Diego, Vilayanur S. Ramachandran, was also interested in this type of optical illusions to design the Mirror Box Therapy, which works to reduce phantom pain.

The mirror box has similarities to the illusion of the rubber hand . In the mirror box the good hand is placed next to a mirror and moves so that the person thinks that he is moving the imputed hand.In this case, the hand of the mirror acts like the rubber hand and, thanks to this, the pain disappears by visual feedback and by eliminating potentially painful positions. With this technique it is possible to give feedback to the brain and relieve the pain that the person feels.

If you want to know more about the mirror box, you can read this article: "The phantom limb and the mirror box therapy".

The Rubber Hand Illusion - Horizon: Is Seeing Believing? - BBC Two (September 2022).

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