Justin Leiber (1993) Conscience and Commissurotomy. Psycoloquy: 4(58) Split Brain (3)

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Psycoloquy 4(58): Conscience and Commissurotomy

Commentary on Puccetti on Split-Brain

Justin Leiber
Philosophy Department
University of Houston
Houston TX 77004.



Puccetti confounds more or less countable brain parts with the functions they more or less subserve. Neonates whose left hemisphere is removed develop language and consciousness in the right hemisphere. Elderly people who suffer the same procedure generally do not. Despite Puccetti's claims, our moral intuitions about the latter are better served by Dennett's theory than by the alternative.


cartesianism, cell death, cerebral dominance, consciousness, hemispherectomy, lateralization, mental duality, mental unity, multiple drafts, split brain.
1. As his book's title brazenly indicates, Dennett (1991) wishes to address, and indeed explain, consciousness, not mind. Since we are well along in an era that takes it for granted that many if not most mental processes are unconscious, the distinction is hardly idle. So it would be absurd for Dennett to hold all mental processes or mind to be "the center of narrative gravity," whereas he has done much to make it arguable that consciousness or self-consciousness is. If Puccetti (1993) had written "consciousness" wherever he wrote "mind," which he ought to have done if he was attacking Dennett's theory, much of what he wrote would sound weak or even absurd. As it is, Puccetti shifts from one to the other as it serves his attack; this piquant alternation allows him to quote Dennett against Dennett.

2. This is particularly apparent in Puccetti's treatment of Dennett's "parody." Dennett imagines the indeed "chilling" possibility that you -- a "full-fledged" conscious self -- are "trapped in the right hemisphere of a body... whose right side is now as remote as the body of a passing stranger... You would like to tell the world what it is like to be you, but you can't!" (p. 425). This is a chilling possibility and Dennett is at pains to show that research into the aftermath of commissurotomy does not support it; if such research did, it would suggest a very different moral evaluation of such surgery. Indeed, Dennett argues that one justification for his own theory is that it gives us good reason to dismiss this chilling possibility. But Puccetti's response is "Dennett's misconception here is based on the assumption that split-brain surgery necessarily implies splitting a single self into two." It is precisely that implication, however, that Dennett wishes to parody and dismiss; he in no way seeks to deny cognitive function to the right hemisphere.

3. Now Puccetti introduces his equally chilling countervision of the exquisitely conscious lifelong mute right brain, who has been aware since his earliest years that he cannot understand the babbling that goes on around him, except perhaps for hearing or contributing an occasional cuss word, and who is largely a pathetic slave of his left brain master. Real born-deaf mutes, of course, aren't this docile, and, given a halfway hospitable environment, develop language function and full-fledged consciousness and agency. In addition, it is well established that neonates who have left hemispherectomies develop language function and consciousness and appear perfectly normal except for a kind of grammar-blindness which only clearly comes out when the semantic and contextual clues with which they compensate are removed. But, of course, these individuals have had what the commissurotomized right brain, with its "few minutes of exclusive biography a week" (Dennett, p. 425) lacks, namely, the time to accrue "the sort of biography of which full-fledged selves are made." Puccetti's elderly left-hemispherectomized aphasic has the time but lacks the plasticity to make use of it. Indeed, far from justifying euthanasia for the left-hemisphere granny, as Puccetti ominously suggests, Dennett's theory serves our moral intuitions rather well. It is precisely because granny is not simply a right hemisphere but has a lovely face, body, and self, a center of narrative gravity now mainly dependent on the past and on others, such as her children, that we owe her respect and selfhood.


Dennett, D.C. (1991) Consciousness Explained. Boston: Little, Brown.

Puccetti, R. (1993) Dennett on the Split-Brain. PSYCOLOQUY 4(52) split-brain.1.

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