The rubber hand illusion: a curious psychological effect

The study of optical illusions It has been of great help to psychology because of what it can reveal about perceptual processes. To give an example, understand how it works Our brain according to the 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 advancement has allowed us to acquire new knowledge and better understand what happens in our brain. A group of psychologists in Pennsylvania (United States) 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 seems that the rubber hand is part of our body, when someone caresses our rubber hand, we will feel that they are caressing our hand real.

Below you can visualize how the rubber hand illusion happens:

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

The rubber hand illusion not only became a gimmick for illusionists, it was an important find because made it possible to understand how sight, touch and proprioception (that is, the sense of body position) are combined to create a compelling sense of body ownership, one of the foundations of self-awareness.

The property of the body is a term that is used to describe the meaning of our physical self and to differentiate it from that it is not part of us. It is what allows us to know that a hammer that we are holding with our hand is not part of our body or, in the case of animals, let them 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 the neuropsychologist at the Karolinska Institute in Stockholm (Sweden), Henrik Ehrsson, “The illusion of the hand of Gum has inspired many researchers, and many studies have attempted 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 found that the greater the intensity with which the rubber hand illusion is experienced, for example by hitting it hard, there is increased activity in the premotor cortex and the parietal cortex of the brain. These areas are responsible for integrating sensory and movement information. But of course, stroking the hand is not the same as hitting it. And although individuals who have experimented with the rubber hand are aware that the rubber hand is not part of your body, the brain regions that are activated by fear and threat, and that correspond to flight, are also activated more.

What happens to the real hand that is hidden?

Another interesting finding is the one that was carried out by a group of scientists from the University of Oxford, who wanted to know what happens to the hand that is hidden 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 its own, the temperature of the real hand, which is hidden, drops. Instead, 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 real hand is touched. These results seem to show that when the brain thinks the rubber hand is a real 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.

Mirror box therapy: another example of optical illusion

Experiments based on illusions have helped patients who have suffered amputations and who continue feeling pain even though the limb is no longer part of your body, which is known as “pain ghost".

The neurologist of the CEnter the Brain and Cognition from the University of California, San Diego, Vilayanur S. Ramachandran also took an interest in these types of optical illusions to design Mirror Box Therapy, which works to reduce phantom pain.

The mirror box has similarities to the rubber hand illusion. In the mirror box, the good hand is placed next to a mirror and moved so that the person thinks that the imputed hand is moving. In this case, the mirror hand 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 alleviate 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 mirror box therapy”.