Tuesday, 8 February 2011

One frequent criticism of psychological research is that much of it is inconsequential. That it produces little more than 'cool' illusions which, although illuminating how are minds work, are little more than party games. Often this may be true, but it neglects to see the influence such illusions have on wider science.

Take for example, the rubber hand illusion. This appears, on the face of it, as little more than a clever psychological trick, a clever illusion that has little merit above its novelty value.

The illusion consists of a subject sitting at a table, with one arm placed on the surface in front of them and the other obscured from view. In its place, a rubber hand is placed, which may be somehow connected to them via a fake sleeve, to make the illusion more convincing. Here is an example of how the setup looks.

The experimenter then begins to either tap or stroke the rubber hand, while simultaneously doing the same motion to the real hand in synchrony, which remains out of sight of the subject. After a few minutes of synchronised stroking of the artificial and the hidden hand, the subject should begin to associate the artificial hand as their own. This occurs to such an extent that even after the experimenter stops stroking the real hand, the subject still 'feels' the sensation when the rubber hand is stroked.

Watch the rubber hand illusion

When people see this illusion, it can be quite fascinating and certainly a novelty, and is probably quite eery for the subject. A skeptic, however, may question the practical application of such an illusion, and then no doubt begin to harp on the money being wasted in social science research.

However, an interesting new piece of research caught my eye, and I feel it highlights exactly how clever trickery such as this can influence other fields of research.

The research, described here, involves attaching a prosthetic arm to an amputee. The remaining nerve endings, which had previously projected to parts of the missing limb, are rerouted to a patch of skin on the remaining portion amputated arm, via a process called reinnervation. Stimulating different parts of this patch of skin will create the impression that the amputee is being touched on various parts of their missing arm.

Where this becomes clever, and where the influence of the rubber hand illusion comes in, is in the design of the prosthetic arm. The prosthesis is fitted with an intricate system of pressure sensors, which communicate with a 'robot' in contact with the innervated patch of skin. When the prosthetic arm is touched, it in turn stimulated the nerve endings which would have corresponded to that part of the amputated arm. So, for example, if the prosthetic arm detects pressure on the thumb, this is relayed to the nerves which previously projected to the real thumb, which are now situated in the proxy patch of nerve endings.

As with the rubber hand illusion, the brain quickly begins to adopt the prosthetic arm as part of the body. However, unlike the rubber hand illusion, the prosthesis can be used by the amputee to carry out the tasks that you and I take for granted, such as manipulating objects, hold and carrying items, and presumably if this technology becomes more sensitive in the future, can become increasingly sensitive to touch.

In future, this technology could be combined with other revolutionary technology, such as other new prostheses that can be connected directly to the brain, as described here. Although each technology is in its infancy, we could be very close to the ability to replace missing limbs with new ones which are naturally controlled by the brain, and retain the sensitivity to touch, as with the real thing.

Next time, then, you hear somebody dismiss a bit of psychological research as a novelty, or as a clever but useless trick, spare a thought for the influence this may have on other fields of research.

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