Note: the following is excerpted (pp. 144ff) from the online, second edition of Beyond Experience: Metaphysical Theories and Philosophical Constraints, copyright © Norman Swartz, 2001.

Postscript (Added, second edition)

This chapter. in which I have argued for (among other things) the conceptual possibility of pains existing outside of one's body, indeed even being shared by two or more persons, has proven exceedingly troublesome for some readers.

      One reviewer of Beyond Experience singled out this chapter for special comment:
... a (rare) place where Swartz's discussion loses credibility is his alleged possible world (see pp. 118ff.) where we would call something a pain that was literally outside of our body. While it is fun and often enlightening to envisage possible worlds, surely the experience of pain, the having a pain, is always in one's brain. In the actual world, pains are private because they are brain states. If Swartz is trying to show only that they might not have been brain states, he would be right. But so long as pains are experiences and not objects of perception, they cannot sensibly be said to be shared (unless by Siamese twins sharing a brain) or public. Pains could not literally be out of the body and at the same time experiences. If we imagine a world where pains are analogous to colours, of course,this is not necessarily true. —Jack Ornstein, Canadian Philosophical Review, vol. XII (2)-(5) (April 1992-Oct. 1992), p. 355.
      By way of defense, I would reply that if pains can be likened (there are of course differences) to tactile sensations, then there is not only a conceptual possibility of having pain sensations outside of one's body, there has been, more recently, actual laboratory evidence bearing on the question. I reproduce here an article (appearing seven years after this chapter was first published and six years after Ornstein's critique) reporting an experiment that demonstrates, not merely the possibility, but the reality of out-of-body tactile sensations. (Sometimes, it turns out, philosophical theorizing presages scientific discovery.)
This Here Hand Is My Hand, I Think

Participants in a recent psychological study will probably never look at mannequins – or their own bodies – in quite the same way again. Before the study, they knew their arms belonged to them and synthetic ones didn't, simply because seeing is believing. Now they're not so sure.

      Researchers at Carnegie Mellon University in Pittsburgh asked subjects to keep their eyes on a rubber arm that was sitting on a table in front of them, With the subject's left arm hidden from view by a screen, the researchers simultaneously stroked both the rubber hand and the subject's hand with a paintbrush. Even though they knew their own hand was being stroked behind the screen, nearly all the subjects experienced the same bizarre sensation: they felt the fake hand was actually their own.

      According to Matthew Botvinick, the Ph.D. psychology student who coauthored the study with advisor Jonathan Cohen, awareness of self seems to depend on intricate conversations between the brain and a range of sensory inputs that it constantly receives. If those conversations become garbled by contradictory messages, the brain is even willing to stretch the bounds of where the body ends and the outside world begins in order to draw a coherent picture.

      "It's like ventriloquism," says Botvinick, who was so spooked by the illusion when he tested it on himself that he let out a yelp and threw the fake hand across the room. "In the experiment, when something touches the fake hand, you feel it, so the rubber hand appears to be an object with which you sense. And when there is an object of that kind, it's usually part of you. That seems to be one basis of self-identification."

      To confirm that the subjects were experiencing a true shift in their perception of themselves, researchers asked them to run their right index finger along the underside of the table until it was directly underneath their left one. Those who had experienced the rubber-hand illusion invariably missed their real finger altogether and pointed more closely to the fake hand.

      "When you look at your hand, it doesn't feel as if your brain might be going through all kinds of complicated computations to arrive at the conclusion that this thing is yours," says Botvinick. "You just know it's your hand." —Jennifer Van Ezra, in the column "Nexus" in Equinox, no. 99 (July 1998), p. 14.