36. See W. Barfield et al., «Presence and Performance Within Virtual Environments,» in Woodrow Barfield & Thomas A. Furness III, eds., Virtual Environments and Advanced Interface Design (New York: Oxford University Press, 1995). See also M. V. Sanchez-Vives & M. Slater, «From Presence to Consciousness Through Virtual Reality,» Nat. Rev. Neur. 6.332339 (2005). Mel Slater, for many years a leading researcher in the field of virtual reality, has recently demonstrated that the feeling of ownership can also be induced for simulated body parts in virtual environments (rather than, as in our experiment, having people still look at their «real» body). Obviously, this permits experiments that would never have been possible in the physical world, including real-time modifications of virtual bodies not only in terms of length, size, and appearance, but also complex motion patterns. As the authors put it: «For the future our work also suggests that people can have their 'self' enter the virtual domain in a genuine sense of the word, and not just metaphorically as in current day computer games and online communities. In combination with BCI [brain-computer interfaces] we envisage a functioning virtual body that is felt as their own by participants, with a significant application in VR training, limb prosthetics, and entertainment.» See M. Slater et al., «Towards a Digital Body: Th Virtual Arm Illusion,» Frontiers Hum. Neurosci. 2:6. doi:10.3389/neuro.09.006.2008.

37. See www.dukemednews.org/news/article.php?id=10218.

38. See, for example, R. A. Sherman et al., «Chronic Phantom and Stump Pain Among American Veterans: Results of a Survey,» Pain 18:83–95 (1984).

39. S. W. Mitchell, «Phantom Limbs,» Lippincott's Mag. Pop. Lit. & Sci. 8:563–569 (1871).

40. See V. S. Ramachandran et al., «Scientific Correspondence: Touching the Phantom Limb,» Nature 377:489–490 (1995); V. S. Ramachandran & D. Rogers-Ramachandran, «Synaesthesia in Phantom Limbs Induced with Mirrors,» Proc. Roy. Soc. Lond. B:377–386 (1996); and V. S. Ramachandran & Sandra Blakeslee, Phantoms in the Brain (New York: William Morrow, 1998).

41. V. S. Ramachandran, «Consciousness and Body Image: Lessons from Phantom Limbs, Capgras Syndrome and Pain Asymbolia,» Phil. Trans. Roy. Soc. Lond. B353:1851-9 (1998). For clinical and experimental details, see Ramachandran and Rogers-Ramachandran, «Synaesthesia in Phantom Limbs» (1996).

42. P. Brugger et al., «Beyond Re-membering: Phantom Sensations of Congenitally Absent Limbs,» Proc. Nat. Acad. Sci. USA 97:6167-72 (2000).

43. See § 12 and § 13 of The Ethics.

CHAPTER 4

1. Adapted from the case report of a sixty-eight-year-old woman suffering from stroke-related, transient alien hand syndrome. From D. H. Geschwind et al., «Alien Hand Syndrome: Interhemispheric Disconnection Due to Lesion in the Midbody of the Corpus Callosum,» Neurology 45:802–808 (1995).

2. See K. Goldstein, «Zur Lehre der Motorischen Apraxie,» Jour. fur Psychologie und Neurologie 11:169–187 (1908); W. H. Sweet, «Seeping Intracranial Aneurysm Simulating Neoplasm,» Arch. Neurology & Psychiatry 45:86-104 (1941); S. Brion & C.-P. Jedynak, «Troubles du Transfert Interhemispherique (Callosal Disconnection). A Propos de Trois Observations de Tumeurs du Corps Calleux. Le Signe de la Main Etrangere,» Revue Neurologique 126:257–266 (1972); G. Goldberg et al., «Medial Frontal Cortex Infarction and the Alien Hand Sign,» Arch. Neurology 38:683–686 (1981). For an important new conceptual distinction, see C. Marchetti & S. Della Sala, «Disentangling the Alien and the Anarchic Hand,» Cog. Neuropsychiatry 3:191–207 (1998).

3. Goldberg et al., «Medial Frontal Cortex Infarction,» 684 (1981).

4. G. Banks et al., «The Alien Hand Syndrome: Clinical and Postmortem Findings,» Arch. Neurology46:456–459 (1989).

5. Ibid.

6. For more on the representational architecture of volition and akinetic mutism, see T. Metzinger, «Conscious Volition and Mental Representation: Towards a More Fine-Grained Analysis,» in Natalie Sebanz & Wolfgang Prinz, eds., Disorders of Volition (Cambridge, MA: MIT Press, 2006).

7. S. Kremer et al., Letter to the Editor, «The Cingulate Hidden Hand,»

Jour. Neurology, Neurosurgery, and Psychiatry 70:264–265 (2001); see also a classical study by I. Fried et al., «Functional Organization of Human Supplementary Motor Cortex Studied by Electrical Stimulation,» Jour. Neurosci. 11:3656-66 (1991). In this study, subjects stimulated with electrical currents of different strength reported the illusory conscious perception of ongoing movement, or the anticipation of movement, or the «urge» to perform a movement, all «in the absence of overt motor activity.»

8. D. M. Wegner & T. Wheatley, «Apparent Mental Causation: Sources of the Experience of Will,» Amer. Psychol. 54(7):480–492 (1999).

9. Wegner & Wheatley, «Apparent Mental Causation» (1999), 488.

10. Ibid., 483.

11. See, for instance, P. Haggard, «Conscious Awareness of Intention and of Action,» in Johannes Rossler & Naomi Eilan, eds., Agency and Self-Awareness-Issues in Philosophy and Psychology (Oxford, UK: Clarendon Press, 2003). A good recent review is Patrick Haggard, «Human Volition: Towards a Neuroscience of Will,» Nat. Rev. Neurosci. 9:934–946 (2008).

12. It is true that indeterminacy exists on the subatomic level, but the mind cannot somehow sneak into the physical world through indeterminate quantum processes. (Nor is chance what we want: Philosophically, randomness in the brain would be just as bad as full determination.) Quantum theories of free will are empirically false as well: There may be different kinds of brains somewhere else in the universe, but in human brains the firing of neurons and so on take place on the macroscopic scale. For such huge objects as nerve cells at 37°C body temperature, quantum events simply play no role.