Persons and Psychological Frameworks:
A Critique of Tye
“As one [split-brain] patient remarked immediately after seeing herself make a
left-hand response of this kind, ‘Now I know it wasn’t me did that!’”
(Sperry, 1968: 733)
1.
Introduction
This paper concerns the relationships between persons, brains, behavior, and psychological
explanation. Tye defines a “psychological framework” (PF) as a set of token beliefs, desires,
intentions, memories, streams of consciousness, higher-order mental states, etc., that “form a
coherent whole” and against which a creature’s “behavior can be explained” (141).1 A person is
the subject of such a psychological framework. Each person has one PF, and with each new PF
there is a new person. Meanwhile materialism tells us, according to Tye, that brains are the
bearers of mental states. In other words, “each person is a brain” (142)—or rather a “global
physical state of the brain,” since Tye believes that a single brain might realize multiple PFs and
thus constitute multiple persons.
Tye draws a very strong evidential link between being a single person and acting in an
integrated fashion. He therefore tries to show that split-brain subjects2, whose day-to-day
behavior is integrated, are single persons. I argue that although split-brain subjects do behave in
what Tye calls a “unified” fashion, they do so despite lacking the minimal kind of psychological
coherence that Tye makes necessary to being a single person. But it is on independent grounds
concerning the causal structure of psychological frameworks that I then argue that split-brain
subjects have two such frameworks. Tye must therefore decide between identifying split-brain
1
All references to Tye, 2003.
2
I use the term split-brain subjects to refer to humans who have undergone callosotomy. The term “subjects” is
meant to be neutral with respect to any claims about personal identity; it is not to be taken as synonymous with
“subjects of experience,” for example. (I use this term instead of “patients” because many split-brain subjects are not
patients; they are simply voluntary participants in split-brain experiments.)
1
subjects with multiple persons—thereby losing the connection between acting in a unified
fashion and being a single person—or dropping the connection between being a single person
and having a single PF. Either way, the psychological frameworks that Tye makes the backbone
of psychological explanation must be individuated partly architecturally, and not just on the basis
of superficial behavioral properties.
Most of this paper simply assumes Tye’s account of personal identity, in order to expose
certain contradictions within what Tye says about personhood in split-brain subjects. Towards
the end of the paper, however, I turn to alternative accounts of persons. While a method of
individuating persons grounded in scientific psychology would identify persons with
psychological frameworks, as Tye does, perhaps an account of personhood grounded either in a
non-psychological science, or in non-scientific psychology, would better fit the interests we have
in personal identity.
2.
“Split” brains and streams of consciousness
“Split-brain” subjects are humans who have had their corpora callosa partially or wholly severed,
and whose cerebral hemispheres therefore function, to a significant degree, independently of each
other. They are famous for the unusual behavioral dissociations they exhibit under carefully
controlled experimental situations. A blindfolded split-brain subject, S, holding a pipe in his left
hand, can’t tell you what he’s holding. When you take the pipe from him and ask him what he
was holding a moment ago, he says he doesn’t know. Yet when you instruct him to reach, with
that same left hand, into a box of objects and to select the object he was holding a minute ago, he
easily does so (under control of his right hemisphere), all the while complaining (via his left
hemisphere) that the task is unfair, since as he has already told you he doesn’t know what he was
holding.
Many philosophers and psychologists have concluded from experiments like these that a
split-brain subject’s two hemispheres are associated with distinct experiences, beliefs, memories,
and so forth. Split-brain subjects are also famous, however, for not obviously evidencing any
cognitive dissociation in their daily behavior (at least not frequently). Once the blindfold is
removed, S tells you he is holding a pipe, and laughs, “I guess it was a pipe I was holding when
2
you asked before. Why didn’t I get that?” You cannot (reliably) obtain any very clear evidence of
dissociation in split-brain subjects unless you go to some lengths to do so, lateralizing perceptual
information to one hemisphere or the other while scrupulously preventing the subject from
engaging in any cross-cuing behaviors. In daily life, that is, split-brain subjects give little
evidence of having two streams of consciousness, though in fact many who have studied the
split-brain phenomena have insisted that the two streams are nonetheless always there.
Tye’s own position on the question of how many streams of consciousness split-brain
subjects have is that for some moments during split-brain experiments, a subject like S has two
such streams, one associated with each hemisphere.3 Tye maintains, however, that a split-brain
subject has one PF and is therefore one person. In this paper I merely assume that Tye is correct
in claiming that the disconnected right hemisphere sustains conscious phenomena and that splitbrain subjects have two streams of consciousness for at least some moments during split-brain
experiments. Both these claims are in fact controversial, but I set them to one side here in order
to focus on Tye’s account of persons and PFs in particular.
3.
Psychological coherence and unified behavior
Tye’s account of personhood, according to which a person is a subject of a PF, relies on the
assumption that a single person has “a set of propositional attitudes with an internal coherence”
(114), though it should be stressed at the outset that he does not require perfect coherence of a
single PF, as we shall see. Tye also relies heavily on unified behavior as evidence of a single PF;
the fact that split-brain subjects generally behave in a unified or integrated fashion becomes, in
Tye’s hands, the major positive argument in favor of their being single persons. But in what
sense is their behavior unified? In the sense, Tye says, that the subjects:
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
3
Elsewhere in Consciousness and Persons Tye argues that outside of experimental situations split-brain subjects
will enjoy a unified consciousness. This unified consciousness is admittedly generated by two functionally
independent patterns of neural activity, but these patterns are redundant in terms of their phenomenal properties, and
3
the visual field. How could this be, if split-brains 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.
(115, emphasis in the original)
This is not much in the way of a definition, however, so I propose that we say that
behavior that isn’t unified is of the type that two or more people might engage in when they are
in some degree of conflict with each other, and that behavior which isn’t like this is unified.4
Thus split-brain subjects normally exhibit unified behavior insofar as they do not usually slap one
hand with the other, or slap their own faces to force themselves to get up after over-sleeping, or
violently shake and come to the aid of a loved one simultaneously, or button their shirt with one
hand while unbuttoning with the other, or struggle to pull their pants up and down at the same
time. Note that I said “usually”: these are in fact all things that split-brain subjects have been
observed to do outside of experimental situations.5 As fascinating as these behaviors are (partly
because they are presumably entirely absent in “normals” i.e. non-split-brain subjects), they are
admittedly rare even in the split-brain population. I will therefore accept that split-brain subjects
therefore are associated with one and the same stream of consciousness. I reject this claim elsewhere (Schechter,
forthcoming), but do not treat this issue here, choosing to focus on Tye’s account of personal identity instead.
4
The account of “unified behavior” I offer here still doesn’t allow us to uncontroversially identify unified or
disunified behavior independent of any beliefs about the behavior’s mental causes, of course. For note that we won’t
even identify two people as being in conflict with each other in the relevant sense unless we perceive their intentions
to be in conflict with each other. (If we see two people who are slammed into each other by a third party or a strong
wind, we won’t see these people as “in conflict with each other” in the relevant, i.e. psychological, sense.) Thus even
on this definition, we won’t perceive a single person as behaving in a disunified fashion unless that person is
behaving in a way we think two people would behave if they were in some kind of psychological conflict with each
other. There is, in general, a bi-directional relationship between individuating behaviors and locating their
psychological causes, which makes it impossible to identify “unified behavior” or “disunified behavior” in an
entirely non-(psychological)-theory-laden way. I don’t pretend then to have offered a definition of “disunified
behavior” that can be used in an entirely uncontroversial way; at this point I am just trying to describe the type of
behavior Tye seems to have in mind when he calls behavior unified or disunified.
5
Bogen, 1987; Dimond, 1980; Gazzaniga, 1970; Bogen, 1987; LeDoux 2002.
4
behave in a unified fashion in their daily lives.
Ultimately, what Tye means when he uses split-brains subjects’ unified behavior as
evidence for their being single persons, is that their daily behavior seems no less the behavior of
a single person than does the behavior of a non-split-brain subject, and that their daily behavior
gives us no reason to think that they have more PFs than do “normals.” Let us grant that this is
the case, and even accept that the unified behavior of split-brain subjects outside of experimental
situations provides powerful evidence that they have single PFs. Is there any other evidence to
the contrary which might outweigh this conclusion?
There is such evidence: evidence showing that, underlying her or his behavior, a splitbrain subject’s cognitive architecture is fundamentally divided. Why, then, is Tye led to the
contrary conclusion? For he does allow that PFs are composed of mental tokens, and
acknowledges at one point that he and his duplicate on twin earth, to whom he is “causally
unconnected”, have different PFs and are therefore different persons, even though both are
subject to all the same types of mental states. Since both sets of tokens are type-identical (and
since Tye allows that a single human being can be associated with multiple persons), these
frameworks are plausibly individuated by reference to the different cognitive or perhaps neural
architectures in which they are located. Here Tye acknowledges a connection between the
psychological frameworks used to explain human behavior, and the causal structure of those
frameworks; he also implicitly accepts a connection between who you are and the causal forces
responsible for your mental life.
Throughout most of his discussion, however, these insights are neglected, and Tye
chooses instead to focus only on superficial properties of persons and of psychological
frameworks. It is because of this shallow focus that he misses (or misinterprets) very compelling
evidence that split-brain subjects have multiple PFs. He is therefore led to offer an unconvincing
account of split-brain subjects’ cognition and behavior during experimental situations, one that
misses the important causal differences between the cognition of split-brain and non-split-brain
subjects.
4.
Persons and subjects of belief
5
The two most obvious positions to take on personal identity in split-brain subjects are that each
such subject is associated with one person, or that each such subject is associated with two
persons. Before I discuss these positions, we should note that there is a third possibility, which is
that split-brain subjects are normally associated with single persons, but are associated with two
persons for at least some moments during split-brain experiments. This third option is regarded
by most philosophers as something of a last choice, however, since it is unclear how sealing a
subject’s nostril or removing her blindfold could call a second person into existence or destroy
her, respectively. There is, furthermore, a fourth possible position on personhood in the splitbrain subject, which is that a split-brain subject is associated with an indeterminate number of
persons (Nagel, 1971). (See also Parfit (1984, 1995), who argues that in any reductionist account
of personal identity, cases of indeterminate identity will be possible.) This paper focuses on the
two main options: that a split-brain subject is associated with one person, and that she is
associated with two persons.
I am still at this point assuming Tye’s account of persons, according to which a person is
the subject of single, coherent PF. (Alternative accounts of persons will be considered in Section
8.) The split-brain experiments seem to provide good evidence that each split-brain subject is
associated with two persons. When S correctly selects the pipe he was just holding (under the
control of his right hemisphere), while protesting (via his left hemisphere) that he doesn’t know
what he was holding, he appears simultaneously to (consciously) believe that he was just holding
a pipe and to not (consciously) believe that he was just holding a pipe. If Tye is correct that
persons are the proper subjects of belief, and that S is (associated with) only a single person,
however, then S cannot both believe and not believe that he was just holding a pipe. For this is a
logical contradiction. In the following sections I shall examine Tye’s attempts to avoid this
contradiction while maintaining his commitments on persons and PFs. I shall argue that these
attempts fail.
5.
Not believing versus believing not
Tye offers two alternative explanations of S’s behavior during the split-brain experiment, neither
of which involves logical contradiction. I reject the first alternative in this section and turn to the
6
second alternative in the next. The first alternative explanation of S’s behavior is that S doesn’t
both believe and not believe that he just felt a pipe; rather, S believes both that he did and that he
did not feel a pipe. And this, Tye says, is normal; “There are many such examples in everyday
life”:
Consider. . . . 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.).
(116)
When faced with what might appear to be a case of S both believing and not believing
that P, Tye says that it is really just a case of S simultaneously believing P and believing not-P.
To do this, he relies on an analogy to normal cases of “contradictory” beliefs, as when I believe
that ice cream is both good (tastes yummy!) and bad (too fattening!).
It is plain that this move cannot work. To start with, every example of holding
contradictory beliefs that Tye offers involves ambivalence. And ambivalence (certainly in these
examples) seems to arise only with respect to an object as a whole (or at least to a plurality of its
features), and not with respect to any individual feature. I am not ambivalent about how ice
cream tastes, nor am I ambivalent about weight gain. Samantha is not ambivalent about how
other white people ought to treat black people. But ice cream and race relations have several
elements, and several effects, and we might feel differently about each of these elements and
effects. I love the taste but not the caloric content of ice cream; I want to eat it but I don’t want to
store it as fat cells. . . .
My ambivalence about ice cream may indeed sometimes lead me to engage in
“disunified” or “contradictory” behavior with regard to it, firmly stating my intention not to eat
any and then eating quite a lot. (Note that this sort of weak-willed behavior arguably does meet
the operational definition of “disunified behavior” I offered earlier: you might yell, “No no, I
don’t want any ice cream!” while I forced it upon you. It is, of course, also depressingly
7
common.) But this is still not like the split-brain subject who was spied trying to pull his pants up
with one hand and down with another simultaneously. When S selects the correct object, while
incorrectly insisting that he can’t, this is not due to ambivalence: it isn’t because he has mixed
feelings about pipes, or likes demonstrating his good cognitive-neurological functioning but
dislikes any compliance with authority.
Second of all—and here the causal difference between S and myself comes into sharp
relief—the term “mixed feelings” makes sense when applied to me, and not when applied to S.
My belief that ice cream is good-because-it’s-yummy and my belief that it’s bad-because-it’sfattening can interact, resulting in my never eating as much ice cream as I say I want and always
eating more than I say I will. When interaction between conflicting mental states is possible,
ambivalence frequently manifests itself behaviorally partly in the form of hesitancy or
reluctance. Contrast this again with S’s behavior when he is blindfolded and asked what he was
just holding in his left hand. He doesn’t say, “Well, I guess it might’ve been a pipe, but I’m really
not sure.” He says, “I don’t know.” If he reaches into the box of objects using his right hand
(directed by his left hemisphere), he doesn’t linger over the pipe (see Sperry, 1968): he rejects it.6
If he reaches into the box of objects using his left hand (controlled by his right hemisphere), he
similarly displays no hesitancy or reluctance: he selects the pipe.
Most importantly, when S is asked at t1 what he was holding at t0 and says he does not
know, surely we don’t want to say that S, or his left hemisphere, believes that he did not feel a
pipe, as opposed to saying that S, or his left hemisphere, does not believe that he felt one. In the
former case we posit possession of an occurrent mental state to explain S’s verbal behavior: the
belief that he absolutely did not feel a pipe. In the latter case we explain S’s behavior by talking
about an occurrent mental state that S lacks: the belief that he felt a pipe. These two ways of
explaining S’s behavior are not explanatorily equivalent, and the second explanation is more
accurate.
Granted, Tye may be right—see page 116—that once you ask S, at t2, “Were you holding
6
It may be that once he feels the pipe with his right hand (using his left hemisphere), S, in rejecting it, has formed
the left hemisphere belief, “I wasn’t holding a pipe.” But even if he forms this belief that not-P at that moment, this
does not show that he had this belief prior to feeling the pipe. I return to this point in a moment.
8
a pipe?”, he will acquire an occurrent left hemisphere belief that he was not holding a pipe at t0.7
But this still would not show that S had this belief prior to being asked. At t1, prior to being
asked about a pipe, specifically, how would S (or S’s left hemisphere) have formed the occurrent
belief that S wasn’t holding a pipe, specifically? The only possibility I can see isn’t a serious one:
S (or S’s left hemisphere) performed some sort of inference from a belief with the content, “I
don’t know what I was holding” to a belief with the content, “I wasn’t holding a pipe.” But
unless an inference to a belief with this particular content happens through sheer magic, S (or S’s
left hemisphere) must have made a similar inference to a seemingly endless number of other
beliefs about what S wasn’t holding: “I wasn’t holding a donut,” “I wasn’t holding a wide-tooth
comb,” etc. An inference (or a series of inferences) of this magnitude will of course not be
computationally tractable. Prior to being asked about a pipe, specifically, S or S’s left hemisphere
may of course have the dispositional belief that he wasn’t holding a pipe, as well as the
dispositional belief that he wasn’t holding a donut, or a wide-tooth comb, etc. But this
dispositional belief is not one to which we can refer in order to realistically explain S’s verbal
denial at t1 that he knows what he was holding. If our mind/brain sciences ever get to a point
where we can actually locate beliefs or belief-instantiating entities in the brain, and you start
looking for the realizers of these two beliefs in a split-brain subject like S—the belief that he felt
a pipe and the belief that he didn’t—you wouldn’t find either in his left hemisphere at t1.8
7
This is not necessarily the case, however: it is possible that once you ask S whether he was holding a pipe,
specifically, he will say yes, using his left hemisphere, even though, prior to being asked, his left hemisphere did not
know that it was a pipe he’d been holding. It is hypothesized that “binary” information can be transferred between
the hemispheres in some instances, and certainly affective states seem to carry over. Thus, when S is asked, “What
were you holding?”, his right hemisphere knows the answer but cannot communicate to his left hemisphere the
correct object, among all the objects in the world; but when S is asked, “Could it have been a pipe?”, his right
hemisphere may be capable of transferring to the left an affirmative answer—either directly or in effect (e.g. by
generating a positive affective state which the left hemisphere then feels and interprets as signifying an affirmative
response). See for example Sperry, Zaidel, and Zaidel, 1979, for examples of the use of affective information to
answer yes/no questions; see Corballis 1995 generally for a review of some of the relevant literature on interhemispheric interaction in split-brain patients.
8
It might be argued that at the very moment when his behavior is disunified, S does not both believe and not believe
that he was holding a pipe just earlier. At t0, S palpates a pipe in his left hand. At t1, when asked what he was holding
a moment ago, S says he does not know. At t2, when asked whether he was holding a pipe, S says “No.” At t3, when
asked to use his left hand to select from a box of objects the object he was holding a moment ago, S selects the pipe.
9
Though Samantha’s behavior towards black people and S’s behavior during the splitbrain experiment may both be “disunified” in some sense, the causal stories explaining those
behaviors are without question very different, and Tye is wrong to conflate them. We explain
Samantha’s behavior by referring to the types of mental states she possesses and to the contents
of those states. Why does Samantha extol equal treatment yet treat the races unequally? Because
of her unconscious negative attitudes towards black people, her conscious belief that
discriminatory behavior towards black people is bad, and her powerful desire to believe that she
is a good person. But to explain S’s behavior, we need to refer to something more: we still need
to refer to the types of token mental states S has, and to the contents of those states, but we also
need to refer to the different hemispheres or to the different psychological frameworks in which
those mental tokens are located. Insofar as S can be characterized as holding “contradictory
beliefs” about whether he just felt a pipe, this is best explained by the fact that S has two
computationally isolated belief-generating systems in which these “contradictory beliefs” are
located. Why does S select the pipe but say he wasn’t holding anything? Because his mental
architecture is fundamentally different from Samantha’s: his beliefs and experiences just can’t
interact in the way hers can. S selects the correct object while saying he can’t because the largest
fiber tract in his brain was surgically severed, resulting in his left and right hemisphere mental
states being unable to interact with each other in the way that they once could, and meanwhile his
right hemisphere has a kind of felt access to his left hand that his left hemisphere lacks.
6.
Psychological vs. Neural Explanation
Perhaps S’s behavior is only disunified between t2 and t3. (Indeed, the experiment could potentially be set up such
that S was both verbally denying having felt a pipe, specifically, and manually selecting the pipe at the very same
moment: t2 = t3, in other words.) Now, the best explanation for S’s selecting the pipe at t 3 is that S believes he was
holding a pipe at t0, a belief he has held continuously since that time; the best explanation for S’s behavior at t 2 is (I
will assume here) that he believes he was not holding a pipe. At t2, therefore, S both believes he was holding a pipe
and believes that he wasn’t—but this involves no logical contradiction, Tye notes.
My argument, though, is that an essential part of the explanation for why S comes to believe at t2 that he was
not holding a pipe at t0 is that at t1, S did not believe that he was holding a pipe. At t1, in other words, S both
believed and did not believe he’d held a pipe—which of course is a logical contradiction. And to deny the need to
acknowledge this, on the grounds that there is not yet any disunified behavior at t1 and no longer any logical
contradiction at t3, is blatant behaviorism.
10
A natural objection at this point would be that the preceding line of argument is premised upon
an uncharitable interpretation of Tye’s proposed explanation for S’s behavior during the splitbrain experiment. It might be said, and Tye may simply mean, that in order to explain why S says
he doesn’t know what he was holding even while correctly selecting the pipe, we need only refer
to S’s neural architecture, and that doing so obviates the need to refer to multiple persons or
psychological frameworks. It might be said, that is, that we need not say either that S believes he
was not holding a pipe, or that S does not believe he was holding a pipe. There is a third
possibility: we say that S does believe he was holding a pipe, but that, due to his
commissurotomy, S is incapable either of accessing this belief or of verbally expressing it. This
provides a coherent way of explaining the degree of behavioral disunity S exhibits under
experimental conditions, one that avoids the mistake of analogizing S’s disunified behavior to
straightforward cases of ambivalence, while also avoiding the prima facie extravagance of
identifying S with multiple persons or PFs (an identification made to look especially extravagant
in light of S’s normally unified behavior).
It is of course true as a general rule that apparently inconsistent attributions of mental
properties may be easily reconciled when we learn more about the neural architecture underlying
them. For example, we can say that a stroke victim with visual agnosia consciously sees a fork,
knows what a fork is, and yet cannot verbally identify it as a fork. We can say all this about the
stroke victim knowing that the stroke has compromised some high-level visual areas of her brain,
depriving her, perhaps, of the visual template for “fork,” and therefore making her incapable of
seeing a fork as a fork, though she can verbally identify a fork by touch. Note, however, that we
can say all this about the stroke victim not just because she has an “unusual” neural architecture,
but because of what we know about that architecture. Thus in the case of a stroke victim who can
verbally identify a fork as a fork after touching it, but not after looking at it, there is of course no
need to postulate multiple subjects of experience, a feeling subject who knows what a fork is and
a seeing one who doesn’t.
Tye sees the split-brain case analogously. Of a case in which the word “pen” has been
projected to only the left visual field/right hemisphere of a split-brain subject, he writes: “The
fact that the split-brain patient doesn’t say ‘pen’, when asked what he saw, doesn’t show that he
11
doesn’t believe that he saw ‘pen’. He does believe that. It’s just [that], given the
commissurotomy, he can’t verbally express that belief” (116). Tye is of course correct that in
general, considerations of neural architecture may obviate any need to postulate multiple subjects
of belief, and other prima facie mental extravagances. But commissurotomy is a particular, not a
general, case, with at least one strikingly different feature from (most) other unusual neural
architectures. While many cases of unusual neural architecture may involve some compromised
access between mental systems, and while the split-brain case does of course involve this, in the
split-brain case each of the mental systems in question—that associated with the left hemisphere
and that associated with the right—is capable of supporting a mind “comfortably characterizable
as human” (Marks 1981: 47, fn. 18). Both hemispheres can sustain (I am assuming along with
Tye) conscious experiences—experiences to which the other hemisphere is not subject. Either
hemisphere can guide intelligent behavior, apparently without the help (indeed, sometimes
despite the hindrance) of the other. There is even evidence that, in split-brain subjects, the
hemispheres separately sustain autobiographical memories and different emotional responses to
these memories (Schiffer et al., 1998). Evidence not only from split-brain studies but from those
rare cases of left or right hemispherectomy following (basically) normal development lends
further support to the conclusion that each hemisphere is at least a candidate for being the subject
of a unique PF (as Tye himself acknowledges in a slightly different context; see p. 150).9 In the
split-brain case, in other words, the very neural architecture, reference to which might be claimed
to make unnecessary the positing of multiple persons or PFs, is in fact one of the strongest pieces
of evidence in favor of there being multiple persons or PFs to begin with.
The fact that there are two potential persons in the split-brain case gives the claim that S
believes he was holding a pipe, but can’t access this belief, two different interpretations, while
the claim that the stroke patient sees a fork and knows what a fork is, but can’t verbally identify it
as such, only has one. In the latter case we readily interpret the claim as stating that the stroke
patient is one and only one person, who sees a fork but does not recognize it as a fork, even
though she knows what forks are. In the former case, however, we are faced with two competing
interpretations of the claim. On the one hand Tye might mean that the whole split-brain subject
9
See Boatman et al., 1999; Burklund and Smith, 1977; Gott, 1973; Smith, 1966, 1969.
12
(the organism) has the belief that he was just holding a pipe, but that this belief can’t be accessed
in all the same ways that, say, my belief that I just saw a bird can be accessed. This is clearly
correct, but not relevant given Tye’s account of personal identity, which is couched in
psychological, not in organismic, terms. (Recall that in Tye’s account it is a global physical state
of the brain, rather than a whole organism, that is the bearer of beliefs and so forth.) The claim
might alternatively be interpreted as saying that there is a single person associated with the splitbrain subject S, and that this person believes he felt a pipe but just can’t access this belief. This
claim is clearly relevant but not clearly correct, since, again, what makes the split-brain case so
different from the stroke case is that in S’s case there are two neural architectures we could
identify with persons. The question is whether we should do so. Before I return, in the last
section of this paper, to that question in particular, I will briefly explain why, contra Tye, and
regardless of which account of personal identity we adopt, we must at least attribute to each of
S’s hemispheres a unique psychological framework.
7.
Individuating psychological frameworks
If we looked only at the types (and contents) of mental states born by each of S’s hemispheres,
we might conclude that these hemispheres are associated with one and the same psychological
framework. While the degree to which the hemispheres will bear the same types of mental states
has probably been exaggerated in some of the commissurotomy literature, given that the
hemispheres don’t just have different perceptual access to the world but are also functionally
non-identical in their cognitive and perceptual processing, still, there will of course be a large
degree of overlap in the types (and contents) of mental states they bear at any one time.
Furthermore, even those states and contents which differ between the hemispheres may not be
incoherent.10
10
I say this because not all differences in, say, the contents of experience, amount to incoherence or inconsistency.
Experiences that differ between the hemispheres may simply be of different parts of the world (and the body), or of
different aspects of the same part of the world. It is largely in the context of personal identity concerns that mere
differences of this sort begin to look like inconsistencies, roughly I think because we equate a person with a subject
of experience, and believe that such a subject’s experiences are all phenomenally unified (or co-conscious) with each
other. The hemispheres of a “normal” subject, then, may also contain different experiences; but we believe that in the
13
But psychological frameworks are not ultimately about type identity or coherent contents.
Of course a psychological framework must include a variety of types of mental state; no set of
informational states, alone, absent motivational states, could explain a creature’s behavior, for
instance. But PFs are composed of mental tokens: particular neural events, individuated by their
functional and intentional properties, and by the particular causal relationships they bear to other
neural events. Mental tokens compose a framework by bearing certain causal relations to each
other; a thought can belong to a framework even if its content is semantically unrelated to or
even inconsistent with the other contents born by that framework, so long as that thought bears
appropriate causal relationships to (some) other states within the framework.
Since causal interaction between mental states occurs both within and between persons,
minds, and bodies, let us distinguish two kinds of causal interactions that can occur between
mental events: direct and indirect interactions. I propose to define “direct” interaction negatively,
in terms of “indirect” interaction. Indirect interactions are interactions between mental events that
supervene on events that no mental state supervenes on, such as behavioral and environmental
events. And direct interactions are interactions between mental events that are not indirect. Note
that while my mental states and my sister’s mental states may interact richly with each other, they
will do so only indirectly. My mental states may also bear many indirect relationships to each
other; there will, nonetheless, be a rich web of direct interactions between my mental states as
well.
This distinction between direct and indirect causal relationships allows a way of
delineating psychological frameworks as causal centers of thought and experience. When we
attend to the causal interactions that occur within and between the two hemispheres of a splitbrain subject, we observe many direct intra-hemispheric causal relationships and few direct
inter-hemispheric causal relationships. In particular, there are few direct inter-hemispheric
relationships at the level of conscious thought and experience.11 The brain of a split-brain subject
“normal” subject there is a single subject of experience for whom these right and left hemisphere experiences are all
co-conscious with each other.
11
Though there are many unresolved complexities and uncertainties regarding the nature of inter-hemispheric
emotional interaction, particularly regarding the individuation of token emotions, I would be happy to concede, at
least for the sake of argument, that conscious emotion may constitute an exception to this general finding. Beneath
14
appears to have two causal centers of cognition and perception, especially conscious cognition
and perception, that interact with each other primarily via behavioral and environmental (and
other non-mental) events. It is in this sense that it is said that S’s two hemispheres each sustain a
cognitive system meeting the criteria for a psychological framework largely independently of the
other—i.e. absent much direct causal interaction. Note that while the criterion for individuating
PFs proposed here does not appeal to psychological coherence, some limited appeal to coherence
could be worked into it; but causal structure and not coherence remains at its heart.
Due to the fact that the “disconnected” hemispheres of a split-brain subject actually
remain connected via subcortical structures, however, their causal independence is not absolute. I
admit, that is, the two hemispheres of a split-brain subject may fall somewhere between the two
hemispheres of a “normal” subject and two hemispheres located in two different human beings,
e.g. myself and my sister, in terms of their capacity for direct interaction. Indeed some (notably
Lockwood, 1989) have constructed models of a split-brain subject’s consciousness according to
which it is neither dual (divided) nor wholly unified but rather partially unified. Someone who
accepted such a model might argue, against both Tye and myself, that there is no precise number
of psychological frameworks that a split-brain subject has.
While I have doubts about the ultimate plausibility of the partial unity model of
consciousness, and believe that the degree to which subcortical structures sustain direct
interaction between the two (cortically) “disconnected” hemispheres is still open to question, I
also believe that split-brain subjects have two PFs in any event. The mental states of various
types that compose a PF must be capable of direct interaction with each other in all the ways
tokens of those types characteristically interact (whatever ways those are). Thus within at least a
human’s psychological framework, it isn’t just emotional or affective states, or primitive
perceptual states, etc., that can interact directly; within a human’s psychological framework some
the level of conscious experience, meanwhile, there may be further direct relationships between the two
“disconnected” hemispheres of a split-brain subject—relationships sustained by (intact) sub-cortical structures.
These structures may sustain apparent unity of the ambient visual field as proposed by Trevarthen and Sperry (1973),
and may permit the transfer of binary information about stimuli, as suggested earlier—and the transfer of response
information (as opposed to stimulus information), which may play a role in guiding unified behavioral responses (see
Corballis and Forster, 2003). For a general review of inter-hemispheric integration in the visual realm (via the
“second visual system”), see Corballis 1995.
15
fairly rich degree of direct interaction between mental states of various types is possible. I can
agree to assume, then, that the hemispheres of a split-brain subject do interact, directly, at the
level of affect, and at the level of some “implicit” mental processes. Cognition at these levels will
still just provide a kind of scaffolding upon which each hemisphere separately builds a further,
unique, rich cognitive structure. We can therefore still locate two psychological frameworks in
the split-brain subject, albeit frameworks whose foundations are not entirely distinct.
Finally, even if this is wrong, and even if split-brain subjects do possess an indeterminate
number of psychological frameworks, my most fundamental objection against Tye still stands:
when he turns to split-brain subjects, he errs in individuating their psychological frameworks
entirely in terms of shallow intentional, rather than functional/causal, properties.
The approach to individuating psychological frameworks that I’ve advocated makes clear
why it is so unappealing to attribute to S one PF most of the time and two PFs during the splitbrain experiment. For while the split-brain experimental paradigm imposes behavioral and
environmental constraints not present outside the laboratory, thus limiting the degree of indirect
causal interaction that can take place between S’s two hemispheres, the one thing it does not
change is the underlying neural architecture responsible for affording direct causal interactions
between mental states. As Rey once said about split-brain subjects:
[their] hemispheres. . . . constitute a significant part of their [personal]
embodiment, and. . . if they are detached from one another, seem to be each
sufficiently complex and sufficiently autonomous to be regarded as separate
persons. At least they seem so for the duration of the experiments. But these
experiments in no way disturb the underlying structures: they simply lay them
bare.
(Rey 1975: 7; emphasis added)
The major objection to attributing to S two psychological frameworks remains that S’s
behavior is generally so unified outside of experimental situations. In fact, as Nagel (1971) once
noted, and as Tye also indicates, it is fairly unified even within experimental situations. But S’s
two frameworks may be highly similar, and having a single psychological framework is, I
16
believe, not the most important unifier of behavior. While behavioral unity no doubt has many
sources, I suspect that it largely emerges out of mental, sensory, and motor processes that need
not involve direct interaction between frameworks or hemispheres (e.g. increasing left
hemisphere dominance, cross-cueing, the strengthening of ipsilateral motor and sensory circuits)
and out of internal, causal forces that exist below the level of cognition and experience (e.g.,
postural reflexes, pattern generators in the spinal cord), and out of constraints posed by
embodiment (e.g., the impossibility of being in two places at one time), and out of regularities in
the environment (e.g., the world is largely the same on both sides of the vertical meridian—
chimeras are rare), including social environment (e.g., one encounters largely the same people
from day to day). And as Gazzaniga (1985) has emphasized, certain general features of human
psychology—such as the desire to see one’s behavior as coherent and rational and voluntarily
generated—must also play a role in unifying behavior. These features of human psychology,
however, also don’t require direct interaction between the two mental systems or hemispheres.
If psychological frameworks are composed of mental tokens, as Tye believes, then a splitbrain subject such as S has two psychological frameworks. This is not simply because S’s
hemispheres are associated with distinct mental tokens, something that may be true of any
subject’s two hemispheres. It is certainly not simply because S lacks a corpus callosum.
Conclusions about psychological frameworks in split-brain subjects would say little, for example,
about psychological frameworks in acallosal subjects (subjects born without corpora callosa),
since the corpus callosum is individuated anatomically, not functionally, and other anatomical
structures in other brains may serve a functional role identical to that played by the corpus
callosum in a “normal” brain (and to that not played by any neural structure in the callosotomized
brain). Because psychological frameworks are composed of token mental states, they must be
individuated causally or architecturally: not just as sets of mental states but in terms of the kinds
of relationships between those mental states that are afforded by a particular neural structure. In
particular, within a single psychological framework, there should be a rich pattern of direct
interaction (in the sense of “direct” defined earlier). In the case of a human subject’s
psychological framework, the interaction should also sustain person-level activity like (especially
conscious) believing, desiring, and experiencing.
17
8.
Three possible modifications of Tye’s account
Our split-brain subject S possesses two psychological frameworks, and the possession of these
two frameworks helps explain S’s behavior with respect to the pipe during the split-brain
experiment. If Tye is correct that “With each different PF, there is a different person” (141), then
S must also be associated with two persons, a right hemisphere person who believes he held a
pipe and a left hemisphere person who doesn’t. Some who have studied the split-brain
phenomenon have argued (with varying degrees of explicitness and seriousness) that split-brain
subjects are associated with two persons apiece—a right hemisphere person and a left
hemisphere person. (See for instance Schiffer (1998), Dimond (1980), Bogen (1990), Rey
(1975), Sperry (1974, 1990), and, most famously, Puccetti (1981, 1989).) Such “duality
advocates,” however, have also accepted a further conclusion, one that directly contradicts a
fundamental commitment of Tye’s. They have accepted that the evidential link Tye draws
between acting in a unified fashion and being a single person can be broken, since split-brain
subjects do generally behave in a unified fashion. Duality advocates see questions about counting
minds and persons not as questions about behavior first and foremost, but rather as questions
about the deep structure of the mental forces responsible for human behavior. This leaves them
open to the possibility of discovering surprising things about the nature, and the number, of these
structures.
An alternative is to identify persons with organisms or animals, rather than with
psychological frameworks or with the parts of animals that realize those frameworks. Such an
account could say that a person is an organism or animal that possesses at least one psychological
framework, and that S is a single person possessing two psychological frameworks. At first
glance this option might seem to require us, again, to face a logical contradiction in order to
provide a realistic explanation of S’s behavior during the split-brain experiment; for a single
person still can’t both believe and not believe that P. But this account could simply make parts of
persons, rather than persons themselves, the proper subjects of psychological frameworks;
18
persons would possess these frameworks without being their subjects, strictly speaking.12 Hence
both the belief that P and the lack of a belief that P can be used to explain S’s behavior, because
one of S’s hemispheres does not believe that P.
Tye might object to this second alternative that identifying persons with whole organisms
can’t account for another population he discusses, subjects with dissociative identity disorder
(DID).13 If persons are whole organisms, then subjects with DID are single persons also; yet their
behavior is disunified (at least across time). This objection is easily met, however. Though
persons aren’t the proper subjects of psychological frameworks on this alternative, persons still
possess (one or more) PFs, and these frameworks play a primary role in our explanations of
behavior. A person with two PFs that are very similar (in terms of the types of mental states and
contents they include) will exhibit more unified behavior than a person with two PFs that are
very different. So we can still explain disunified behavior wherever we need to.
Of course, accepting this modification to his account would still require Tye to give up
something significant: it would require him to give up the connection between persons and
coherent sets of psychological states. For, according to the account of persons now being
considered, a person can, broadly speaking, possess incoherent pairs of mental states, by virtue of
12
Dainton has suggested something similar: “If the relevant mental capacities are grounded in only a small part of
the animal, and this small part is, at least in principle, detachable from the remainder, then can we not say the
following. Yes, animals have mental capacities, but strictly speaking, the whole animal does not possess these
capacities, only a part of the animal possesses them; so in saying that ‘Animals have mental capacities’, what we are
really saying—or would say on reflection—is that ‘Animals have mental capacities by possessing a part which has
these capacities’” (Dainton 1998: 681-682). Dainton says this in the context of defending a kind of psychological
account of persons; he suggests identifying the part of the animal that has these capacities with the person. This
suggestion would be equivalent to the first possible modification of Tye’s account, which maintains that persons are
the subjects of psychological frameworks and therefore accepts that a split-brain subject is associated with two
persons. The alternative modification I’m suggesting here is that we identify the animal with the person—a person
who possesses two cerebral hemispheres, each of which believes, experiences, and so forth.
13
While the basics of the split-brain phenomena are fairly robust, dissociative identity disorder (DID) is somewhat
of a minefield diagnostically and theoretically. It remains a controversial diagnosis, with skeptics insisting that a
better explanation of DID behavior can be given in terms of hysteria, amnesia, repression, and more common and
mundane forms of dissociation. I remain agnostic on DID as a diagnosis in this paper and here confine myself to
explaining why identifying persons with whole organisms does not leave us without the means to explain the
19
possessing multiple psychological frameworks whose contents do not cohere with each other. For
this reason, this second alternative may be thought more extreme than the first, even though the
first identified S with two persons.
But persons may well be surprisingly complicated. Numerous cases of mental pathology,
from blindsight to agnosia, suggest that all those activities that make up Tye’s “coherent
psychological frameworks”—belief, perception, experience—are built up and break down in
pieces. Such cases involve damage to particular areas and pathways of the brain, damage to
particular physical parts of organisms, resulting in partial but not full loss of desire, experience,
memory, and belief. Arguably the split-brain cases are so fascinating, and even disturbing, from
the standpoint of personal identity, precisely because they bring into sharp relief the fact that we
do in some sense see and desire and believe with parts of ourselves, and not with our whole
being. When some of these parts stop perceiving and desiring and believing, it isn’t clear what
happens to us. Identifying persons with animals means saying that we remain single persons even
when our psychological aspects are deeply divided.
A final possible modification to Tye’s account of personal identity would both respect the
strong evidential weight that account puts on behavioral integration, and keep something like a
rough psychological coherence condition for the individuation of persons, while still dissociating
persons from psychological frameworks. According to this third alternative, a human organism
with multiple PFs might still be a single person, so long as those PFs were psychologically
similar to each other, particularly with regard to those psychological properties that most matter
to us about persons: character and personality traits, values, long-term memories, emotional
attachments, and deeply felt desires and dreams. The psychological properties we would pay
most attention to, then, to determine whether a human being was one or more persons, would be
intentional (and historical) first and foremost. Going this third route could mean saying that splitbrain subjects are single persons, since their two frameworks appear composed of significantly
overlapping types of mental states and events, while saying that subjects with dissociative
identity disorders are multiple persons. (Indeed a patient with DID might be multiple persons
even if she had only a single psychological framework, depending on the architecture and
behavior of subjects diagnosed with DID, or even without the means to accommodate the essentials of that diagnosis
20
contents of that framework.)14
According to this third possible modification of Tye’s account, while the individuation
criteria for persons differ from those for psychological frameworks, the individuation criteria for
persons are still psychological. Thus this third alternative allows Tye his conclusions about
personhood in the two kinds of “hard cases” he discusses, and retains that aspect of his account
of personal identity that grounds personhood in (some) psychological facts. But it rejects that
aspect of his account of personhood that says that there is a unique person associated with each
psychological framework, since different sorts of psychological facts will be relevant depending
on whether it is persons or PFs being individuated.
Note that this third alternative does not ground the individuation of persons in the
findings of (scientific) psychology or neuroscience. (The second alternative doesn’t either, but it
may ground the individuation of persons in biology.) This may be wise; Nagel (1971) suggested
long ago that our notions about persons may be incompatible with the results of ongoing
psychological and neuroscientific discovery. It is possible, then, that to the degree that Tye
presents his account of persons as grounded in scientific psychology, he does so unwisely. For
the interests we have in persons may well be largely “forensic,” as Locke once said (1690), and
therefore not closely tied to the outcome of any scientific debate. In fact I myself am sympathetic
to such a view of personhood, and suspect that while some findings in some areas of psychology
will be relevant to our beliefs about persons, “person” will not survive in, nor have any
terminological descendent in, the vocabulary of a developed scientific theory. This is not
surprising, because, again, our interests in persons are largely moral, social, and simply personal
in nature. Against the background of such interests, split-brain subjects may be single persons not
simply because their behavior is usually so unified outside of experimental situations, but
because even that behavior of theirs that is “disunified” does not usually reflect, and the division
between the two hemispheres is not founded on, differences in values, temperament, character, or
if in fact it is real.
14
While I am reluctant to say much about DID at this point in time, I do think that there is some evidence to suggest
that there may be a kind of deep functional unity underlying the apparently oppositional “alters” of such subjects. We
might identify a DID subject with one PF but with multiple persons, however, given the type of interests we tend to
have in persons.
21
history. Nagel commented, and Tye repeats, that the friends and family of split-brain subjects
relate to them as if they were single persons; this manner of relating to them seems not just
natural but fully rational, regardless of what scientists discover about the deep structure of their
mental lives: for the two hemispheres share not just a body, but a personality and a history.
These three options I’ve just described all amount to the same thing in one crucial
respect: they all attribute to S two distinct psychological frameworks. Accordingly, any of the
three possible modifications of Tye’s account of personal identity will require Tye to change not
just what he says about split-brain subjects, but also what he says about persons: the links
between being a single person, having a single psychological framework, and behaving in an
integrated fashion must be broken somewhere.
My deepest criticism of Tye’s account of personal identity as applied to split-brain
subjects is not that he identifies them with single persons. His intuition that split-brain subjects
are single persons is quite understandable. But in order to defend this intuition Tye is forced to
claim that split-brain subjects have single PFs, because of the account of personal identity he
adopts. My deepest criticism of Tye’s account, then, concerns his treatment of PFs. Psychological
frameworks, or something like them, I take it, are constructs of a (developing) scientific
psychology, and accordingly will be individuated by reference to intentional properties, but also
to both cognitive architecture—to the types of relationships possible between mental tokens of
various types—and the underlying neural structure sustaining that architecture. So individuated, a
unique PF is associated with each hemisphere of a split-brain subject: each is even the bearer of
person-level properties and activities such as believing, perceiving, feeling, desiring, and
remembering.15 Moreover, the interaction that occurs between them largely supervenes on
behavior or environmental events, or on internal events not describable as mental.
Ironically, individuating psychological frameworks architecturally, instead of (largely)
behaviorally or by content type, would actually allow Tye to provide better behavioral
explanations than he is currently able to. Since he takes S’s generally unified behavior to be
15
Note that this does not appear to be true of any smaller part of a human brain: no part smaller than a whole
hemisphere is a believer and a desirer and a perceiver, etc. Nagel’s (1971) worry that if we identify each hemisphere
with a mind we will soon have to identify the visual system alone with a mind, for example, is not warranted; there is
no slippery slope here because the visual system alone is not a candidate for being the subject of an entire PF.
22
overriding evidence that S has a single PF, he is forced to resort to an unconvincing
psychological explanation of S’s behavior during the split-brain experiment. Locating
psychological frameworks at a deeper level gives us a better understanding of the psychological
mechanisms responsible for split-brain subjects’ behavior and, accordingly, a better explanation
of that behavior.
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