The illusion of the rubber hand: a curious psychological effect

The study of optical illusions this has been of great help to psychology for what they can reveal about perceptual processes. To give an example, understanding how our brains work with proprioception has been very helpful for patients who have had amputations. Through 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 advancements have allowed us to gain new knowledge and better understand what goes on in our brains. A group of psychologists from Pennsylvania (USA) discovered a curious illusion, known as the “rubber hand illusion”.

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

Below you can see how the rubber hand illusion occurs:

The rubber hand illusion, more than just a trick for illusionists

The rubber hand illusion not only became a trick for illusionists, but it was an important discovery because understand how sight, touch and proprioception (i.e. the sense of body position) combine to create a compelling sense of ownership of the body, one of the foundations of self-awareness.

Body ownership is a term used to describe the meaning of our physical self and differentiate it from being part of us. This is what lets us know that a hammer that 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 legs because they belong to their own body.

The discovery of the rubber hand illusion has inspired many researchers

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

Scientists have found that the greater the intensity with which the illusion of the rubber hand is felt, such as hitting it hard, the greater the activity in the premotor cortex and in the parietal cortex of the brain. these areas they are responsible for integrating sensory and movement information. But of course, stroking her hand is not the same as hitting it. And while individuals who have performed experiments with the rubber hand are aware that this hand is not part of their body, the regions of the brain which are activated by fear and threat, and which correspond to theft, are also more activated.

What about the real hand that is hidden?

Another interesting discovery is the one made by a group of scientists at the University of Oxford, who wanted to know what happens to the hidden hand during the experiment. If the brain reacts to the rubber hand, does it also react to the hidden hand? Well, it seems that just when the brain mistakenly recognizes the rubber hand as its own, the temperature of the authentic hand, which is hidden, drops. Instead, the rest of the body stays the same.

In addition, when the experimenter stimulates the hidden hand, the subject’s brain takes longer to react than when the other genuine hand is touched. These results seem to show that when the brain thinks that the rubber hand is a genuine hand, it forgets the other hand.

This has been very interesting for medicine because it shows that the thermal regulation of the body also depends on the brain.

Mirror box therapy: another example of an optical illusion

Experiments based on the illusion have helped patients who have had amputations and continue to experience pain even though the limb is no longer a part of their body, known as “phantom pain”.

Neurologist at the Center for Brain and Cognition at the University of California at San Diego, Vilayanur S. Ramachandran, also took an interest in this type of optical illusion to design the Mirror Box Therapy, which aims to reduce phantom pain.

The mirror box has similarities with the rubber hand illusion. In the mirror box, the correct hand is placed on the side of a mirror and it moves so that the person thinks they are moving the imputed hand. In this case, the mirror hand acts as a rubber hand and, thanks to this, the pain disappears by visual feedback and eliminating potentially painful positions. With this technique, it is possible to give feedback to the brain and relieve the pain felt by the person.

If you want to know more about the mirror box, you can read this article: “Phantom Limb and Mirror Box Therapy”.

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