Synaesthesia and External ‘Projection’ of Kinesthetic Sensations in Phantom Limb Patients and Normal Individuals

By combining brain imaging (MEG) studies with psychophysical experiments we have shown that, very soon after amputation of an arm in humans, the sensory input from the face begins to activate the original ‘hand area’ of the cortex. Many patients with a phantom arm are unable to ‘move’ their phantom arm. We used a mirror to allow the patient to see the reflection of his normal hand superimposed on the phantom. If he now moved the real arm he not only saw the phantom moving but also experienced vivid kinesthetic sensations in the phantom—a remarkable example of synaesthesia. Finally, we had a normal subject look at his own reflection superimposed on a Halloween mask seen through a half-silvered mirror. If he now made vigorous lip and tongue movements he felt his kinesthetic sensations ‘projected’ on the mask; and his ‘free will’ controlling the dummy's face (it is as though the subject regards it as highly unlikely that his own lip sensations and motor commands should be so perfectly synchronised with the movements of the mask, simply by chance). If the mask was now punched in the eye, the subject registered a strong GSR (galvanic response) demonstrating that his ‘self’ had now temporarily cast off its mortal coil to inhabit the mask.

In our last experiment we had a blindfolded subject repeatedly tapping and stroking the nose of an accomplice who was sitting in front of him. If the experimenter then taps and strokes the subject's nose in perfect synchrony, the subject starts experiencing an absurd lengthening of his nose (the phantom nose). This simple experiment demonstrates the single most important fact about the mechanisms of perception—that they can discern statistical regularities in the world with astonishing rapidity.