5.2 Multiple Personality Disorder, Split Brains, and Unconscious Automata

7. Consider, to begin with, a case of multiple personality disorder. Suppose that Richard Readiweather is a loud­mouthed, beer-swilling, football-loving auto-worker from Michigan. He cares not at all what others think of him, least of all his mother, to whom he pays no attention, visiting her only once a year. His favorite football team, so he says, is the University of Michigan and he is an avid fan. All is not well with Richard. At times, he becomes quiet and introspective. On these occasions, he says that his name is "Claude" and he insists that he hates football and beer. When asked why he goes to all the University of Michigan games, he explains that if he didn't go, it would upset his mother, who is an avid supporter of Michigan football (even though she is her­self too old now to attend the games), and he definitely does not want to offend his mother. When queried about his see­ing his mother only once a year, he says that she needs her space and that he thinks lovingly of her all the time. Concerning the ten beers he drinks on a daily basis, he

insists that he hates the taste of beer, but he believes that it is of great medicinal value. Ten beers a day keeps the doctor away, he says, in a soft, somber tone.

(7) These differences and others of a similar sort between Richard and Claude make it very difficult to suppose that there is but a single person, a single mind present. Richard and Claude each have a set of propositional attitudes with an internal coherence. Where one has a given attitude, the other, in many cases, lacks it. Richard likes the taste of beer; Claude does not. Richard is indifferent to his mother; Claude loves her. Richard enjoys football and he believes that football is a wonderful game; moreover, he wants to see the University of Michigan football games more than any other. Claude doesn't enjoy football, he doesn't believe that football is a wonderful game, and he doesn't really want to see the University of Michigan games, but he goes anyway for his mother's sake. One and the same person cannot both believe that P and not believe that P or desire that P and not desire that P in the way that Richard and Claude do. Richard and Claude thus are two persons, with two minds.

8. Split-brain patients are not like this. Overall, their behavior is just like that of normal people. There is a unity, an integrated character to the functioning of split-brain patients outside of certain very special, experimental situa­tions. They walk, run, swim, play the piano, and engage in any number of everyday activities in the normal way. Moreover, they do not report any breakdown or division in the visual field. How could this be, if split-brain patients are really two different persons? Split-brain patients typically act as if they are single persons with a unified conception of the world and what is going on around them. Those who know split-brain patients cannot help but think of them and relate to them as single subjects (Nagel 1971).

9. Still, it might be insisted, in the relevant experimental situations at least, it must be conceded that two persons are present, even if before the experimental controls are imposed and after they are removed, there is just a single person. For consider again the split-brain patient who has the word 'pen' flashed on the left of the screen and the word 'knife' on the right. He believes that he saw 'pen' (since he reaches for a pen with his left hand when asked to pick out from a group of objects the one corresponding to the word he saw) and he believes that he saw 'knife' (since, when asked what he saw, he verbally reports, "the word 'knife'"). Given that he doesn't say 'pen', when asked what he saw, it seems that he doesn't believe that he saw 'pen'. And given that he doesn't reach with his left hand for a knife in the group of objects, it seems that he doesn't believe that he saw 'knife'. One person cannot both believe that P and not believe that P at the same time. So, the split-brain patient is really two persons, albeit for a short period of time.

(10) There is a mistake in this reasoning. The fact that the split-brain patient doesn't say 'pen', when asked what he saw, doesn't show that he doesn't believe that he saw 'pen'. He does believe that. It's just, given the commissurotomy, he can't verbally express the belief. To be sure, if the patient is asked whether he saw 'pen', he will respond 'no', and this is evidence that he believes that he didn't see 'pen'. But believ­ing that not-P isn't the same as not believing that P; nor does the former necessitate the latter. Likewise, the fact that the split-brain patient doesn't reach for a knife, when told to pick out with his left hand the object corresponding to what he saw, doesn't show that he doesn't believe that he saw 'knife'. The fact that he declines taking a knife with that hand, when offered one as a candidate for the object corresponding to the word he saw, shows that he believes that he didn't see 'knife'. But one and the same individual can certainly believe that P and believe that not-P at the same time (or desire that P and desire that not-P). There are many such examples in everyday life. Consider Jonathan's wanting a Ferrari and his wanting not to have Ferrari (given the unreliability of Ferraris, the cost, the worries involved, etc.); or Samantha's saying sin­cerely that people, whatever their skin color, should be treated alike, while always choosing to sit next to white peo­ple on the bus she takes to work. Or take my believing that sunny weather is wonderful, as I sit relaxing by the pool, and my also believing at that time that sunny weather is not so terrific (given its effects on the skin, etc.). The latter belief, of course, may not be manifested in any conscious thought I have, as I enjoy the sunshine by the pool. But it would have been, had I turned my thoughts to the issue of health.

11. So, the first hypothesis about split-brain patients (which is endorsed by Sperry 1968)¹ is a nonstarter. What of (b), the hypothesis that the responses produced by the right hemisphere are those of an unconscious automaton? Again, this cannot be right. The right hemisphere responses are not especially intelligent and, of course, speech production lies beyond its power. But speech comprehension takes place there, and the right hemisphere can perform a variety of tasks demanding dexterity and discrimination, for example, spelling out words with wooden or plastic letters. The right hemisphere has no difficulty in following the experi­menter's instructions and in performing tasks for which attention and concentration are needed (e.g, picking out the relevant object from a group of concealed objects). If con­sciousness is denied to the right hemisphere, there seems no reason not to extend the denial of consciousness to mutes or to prelinguistic children.