Oliver Sacks - Hallucinations

It is not clear why some people born without limbs have phantoms and some do not. What is clear, as Funk, Shiffrar, and Brugger observed in one study, is that those who do have phantoms seem to have cerebral “action observation systems” similar to those of normally limbed people, allowing them to grasp action patterns by observing others and to internalize these as mobile phantoms. Those born without limbs who do not have phantoms, Funk et al. propose, may have problems in motion perception, especially judging the movements of other people’s limbs.

When Henry Head introduced the term “body image” (fifty or so years after Weir Mitchell had introduced the term “phantom limb”), he did not mean it to refer to a purely sensory image or map in the brain — he had in mind an image or model of agency and action, and it is this which needs to be embodied in an artificial limb.

Philosophers like to speak of “embodiment” and “embodied agency,” and there is no simpler place to study this than in the nature of phantoms and their embodiment in artificial limbs — prosthesis and phantom go together like body and soul. I have wondered whether some of Ludwig Wittgenstein’s philosophical notions were suggested by his brother’s phantom arm — thus his final work, On Certainty , starts from the certainty of the body, the body as embodied agency.

Wade Davis describes this in his book Into the Silence: The Great War, Mallory, and the Conquest of Everest .

Nonetheless, Nelson regarded his phantom as “a direct proof for the existence of the soul.” The survival of a spiritual arm after a corporeal one was annihilated, he thought, epitomized the survival of the soul after bodily death.

For Captain Ahab, however, this was a matter for horror as much as wonder: “And if I still feel the smart of my crushed leg, though it be now so long dissolved; then, why mayst not thou, carpenter, feel the fiery pains of hell forever, and without a body? Hah!”

This story, “The Man Who Fell Out of Bed,” is related more fully in The Man Who Mistook His Wife for a Hat .

Several people have written to me with similar stories of sensing a presence just as they are going to sleep or waking. Linda P. observed that once, as she was drifting off to sleep, she felt “as if I was being held on my right side, as if someone had put their arms around me and was stroking my hair. It was a lovely feeling; then I remembered that I was alone, and [the feeling disappeared].”