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Science Frontiers ONLINE No. 103: Jan-Feb 1996 |
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Seeing Is Feeling
It's all done with mirrors! By properly positioning a mirror, an arm amputee can see the image of his flesh-and-blood limb appearing where his lost limb would normally be -- in a sense visually resurrecting the lost limb. In this way, scientists can explore the effects of vision upon the multitude of very strange "phantom-limb" phenomena reported by amputees. V.S. Ramachandran et al have described some of their findings in Nature.
"Nine arm amputees were studied. A tall mirror was placed vertically on the table, perpendicular to the patient's chest, so that he could see the mirror reflection of his normal hand 'superimposed' on the phantom. In the first seven patients, when the normal hand was moved so that the phantom was visually perceived to move in the mirror, it was also 'felt' to move; that is, a vivid kinaesthetic sensation emerged. (These sensations could not be evoked with the eyes closed.) In patient D.S., kinaesthetic sensations were evoked even though he had not experienced movements in the phantom for the preceding 10 years."
Several patients that experienced pain in their phantom limbs (pain that can be excruciating) found that the pain disappeared when they could "see" their phantom limb in the mirror. Those who complained of the so-called "clenching spasms" in their phantom hands (compared to fingernails digging into the phantom) found the spasms eliminated upon "seeing" their phantom hands.
In some patients, touching the normal hand evoked touch sensations at the same spot on the phantom hand. In others, though, the amputees felt nothing unless the phantom hand was also seen to be "touched" simultaneously. Even more curious, although the sensations of touch and vibration can be "transferred" from real limbs to phantom limbs, the senses of pain, heat, and cold cannot!
(Ramachandran, V.S., et al; "Touching the Phantom Limb," Nature, 377:489, 1995)