Free The Illusion of Conscious Will by Daniel M. Wegner

of the existence of the phantom is not dependent on this nerve/muscle connection—just the sensation of voluntary movement. This finding suggests that there may be a role for information returning from the muscles in producing the sensation of phantom voluntary movement (Devor 1997; Jones 1988).
    It turns out, however, that information coming from simply looking at a moving limb can create the sense of voluntary movement. An early hint that this might be possible appeared in a remarkable study by Nielson (1963), in which people with normal limbs were fooled into thinking that someone else’s hand was their own. People in this study were asked to don a glove, insert their hand in a viewing box, and then on a signal, draw a line down a piece of paper. Unbeknownst to them, the hand they saw in the box was actually a mirror reflection of another person’s hand, also gloved and holding a pen, which appeared in just the spot where they would expect their own hand to be ( fig. 2.3 ). When the signal was given and this imposter hand started to draw a line that departed from the line the participant had been instructed to draw, participants typically adjusted their (own) arm to compensate for the observed arm’s mistaken trajectory ( fig. 2.4 ). The visual feedback from the false hand was so compelling that participants briefly lost contact with their own movement.

    Figure 2.3
    Nielson’s (1963) mirror box had a subject (S) look down at a mirror (M 2 ), ostensibly to see his or her hand underneath, while actually viewing the hand of an assistant (A). Courtesy Scandinavian Psychological Association.
    In a series of studies, V. S. Ramachandran and colleagues (1996; Ramachandran and Blakeslee 1998; Ramachandran and Rogers-Ramachandran 1996) used a different sort of mirror box to examine the experience of phantom limb movement. In one study, an individual with a phantom arm inserted both the phantom and his real other arm into the mirror box. The mirror in this case was placed so that a reflection of the person’s real arm appeared in the place where the phantom would be if it were real. The odd result of this was that when the person moved the real arm voluntarily, he experienced the phantom as moving voluntarily as well. The hand in the mirror seemed to extend from the person’s stump and was felt as if it were being flexed and moved on purpose. The visible hand guided the experience of the phantom.
    There is the possibility here that the person experienced the movement through some brain pathway that produces symmetries in movements between the two hands. To check on this, in two cases, Ramachandran’s group arranged for an experimenter’s arm to appear in place of the phantom.

    Figure 2.4
    Nielson’s (1963) subjects each tried to trace the vertical line while the assistant’s hand wandered off on the dotted path to the right. The points on this graph show the final stopping places of the subjects—most of whom seem to have tried to compensatefor theapparentwanderingbymovingtotheleft.Courtesy Scandinavian Psychological Association.
    They found that “the visual cue was sufficiently compelling that it created a vivid feeling of joint movements in the phantom whether or not the patient moved the contralateral hand (and even though no commands were sent to the phantom). One of the patients noted, however, that the joint sensations were less vivid when the experimenter’s hand was used than when he himself moved his fingers” (Ramachandran et al. 1996, 36). 4 The point to remember, in sum, is that willful movement can be experienced merely by watching any body move where one’s own body ought to be. This is not too surprising in view of the discovery (in monkeys) of the existence of mirror neurons —neurons that are activated both by own movement and by the perception of that movement in another (Rizzolatti et al. 1996).
    4 . The tendency for the eyes to run off with the rest of the body is something you can experiment