The Phantom Hand [Preview]

The feeling of being touched on a fake hand illuminates how the brain makes assumptions about the world

Question Assumptions
The experiment was inspired by earlier work we had done with patients who had phantom limbs. After a person loses an arm from injury or disease, he may continue to sense its presence vividly. Often the phantom seems to be frozen in a painfully awkward position. We asked a patient to put his phantom left arm on the left side of a mirror propped vertically on a table in front of him. He then put his intact right arm on the right side, so its reflection was seen in the mirror superimposed on the phantom, creating the visual illusion of having restored the missing arm. If the patient now moved his right arm, he saw his phantom move. Remarkably, this “animated” the phantom so it was felt to move as well—sometimes relieving the cramp. Even more surprising: in some cases, if the physician touched the real hand, the patient not only saw his phantom being touched but experienced the touch as well. Again the brain regards this combination of sensory impressions as unlikely to be a coincidence; therefore, it quite literally feels the touch emerging from the phantom hand.

Consider what these illusions imply. All of us go through life making certain assumptions about our existence. “My name has always been Joe,” someone might think. “I was born in San Diego,” and so on. All such beliefs can be called into question at one time or another for various reasons. But one premise that seems to be beyond question is that you are anchored in your body. Yet given a few seconds of the right kind of stimulation, even this axiomatic foundation of your being is temporarily forsaken, as the table next to you seems to become part of you. As Shakespeare aptly put it, we are truly “such stuff as dreams are made on.”

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