On Saving Our Concept of a Person

Abstract

In a trenchant and resourceful critical treatment, Dr Kathleen V. Wilkes ('Consciousness and Commissurotomy', Philosophy April I978) struggles to reinterpret the split-brain data so that my extrapolation from these to the normal human organism will not threaten to 'fracture' or 'fragment' the ordinary concept of a person. Similar concerns are beginning to emerge in other quarters1 as well. For the sake of accuracy, and in order to avoid unnecessary misunderstandings in future, I should like to set the record straight. First, a few niggling technical corrections. It is unnecessary to speak of 'commissurotomy surgery', since disrupting the commissural fibres between the half brains is of course going to be effected surgically (how else would it be done, by dynamite?). However, it is necessary to stipulate, at least at the beginning, that this is cerebral or forebrain commissurotomy, because commissural fibres at brainstem, cerebellar and spinal cord level are not transected in human beings (actually the fibres are not usually cut, but sucked out with a long aspirator). Also it is the case that visual stimuli impinging on the left half of each eye's retina do not go to the right, but to the left cerebral hemisphere (and vice versa), since the retina is concave and each half retina receives light from the contralateral side of the body. Furthermore, there is at least one split-brain patient who is a left-hander and has speech concentrated in the right hemisphere,2 but in fact most sinistral people have speech predominantly in the left half-brain just as dextrals do.3 So much for technicalities. At the heart of Wilkes's objections is the notion of 'unity of consciousness', which she thinks underlies the idea of a