Split Brains and the New Paradigm


A few weeks ago I was hiking with a friend and we were discussing the nature of human consciousness, and I mentioned that the split-brain studies seemed to show that consciousness was not unified. My friend said that he had never heard of these studies.[1] I was surprised; the first studies of split-brain patients, and the writings based on them were completed fifty years ago, and to me the resulting dialogue and literature should be a part of the background of our culture--much like, say, the theory of relativity was part of the public consciousness by the 1950s. So, why is our culture not abuzz with the implications of the literature about these studies? In what follows, I will try answer this question, and to indicate some of the problems in adopting a view of the mind that the evidence from the split-brain experiments would indicate is the accurate view about the mind.

So, first, what are the studies? There have been so many that I cannot document them all here.[2] However, let me first describe the procedure that results in a "split-brain," and then describe a few experiments. The medical procedure that results in what is called a "split-brain" is where the corpus callosum, which connects the left hemisphere of the brain and the right hemisphere is severed (it may be completely or partially severed). These procedures were originally performed as a last resort for people with severe epilepsy--the procedure often reduced the severity of the epileptic seizures. The corpus callosum is a bundle of nerves that allows the left and right brain to "communicate" with each other. So, if the corpus callosum is completely severed, one could loosely say that the left hemisphere and the right hemisphere did not "know" what each other is "thinking." We will see what this means when we review a few of the experiments.[3]

The original studies of split-brain patients' behavior was only begun when some researchers noticed some odd behavior of the patients after the completion of the medical procedure. For example, a patient might bump into an object on the left side of their body, and seemingly not notice it, or not report it to the researcher. It seemed as if the patient was unaware of the "bumping" event. So, the researchers wanted to discover what was going on. This all let to the first experiments, or studies of the patients' behaviors.

The basic things to remember about these experiments are that the right hemisphere of the brain controls the left side of the body, and the left hemisphere controls the right side of the body. The experiments I'm going to discuss are loosely referred to as the "key-ring" experiments, and they were experiments examining the patients' visual perception.[4] A human's eyes are basically divided into two halves. The right hemisphere of the brain "sees" what the left half of each eye "sees," and the left hemisphere "sees" what the right half of each eye "sees." The left hemisphere is called the dominant hemisphere, because it is the location of the language ability humans have. The right hemisphere is called the sub-dominant because there is little language ability there.

Here is how one experiment is set up. A subject is put before a screen upon which words can be flashed. The screen has two halves, each half having one word. The words are flashed too quickly for eye movement. This is important, because if the words stayed on the screen for too long, the subject's eyes could move and then both halves of the brain could "see" both words (i.e., each half of each eye sees only one half of the screen). The object is to have each hemisphere see separate words--and since the corpus callosum has been cut, there is no communication of information between the hemispheres.

So, imagine the words "Key Ring" are flashed on the screen. The left half of each eye sees "Key." "Key" is "seen" (processed) by right hemisphere (subdominant). The right half of each eye sees "Ring." "Ring" is "seen" by left hemisphere (dominant, because this is the "language center"). Now, if asked about what has been seen, the subject says, "Ring" (because "Ring" was "seen" by the left hemisphere, and this hemisphere controls speech). The subject does not say "Key Ring" Nor is "Key" spoken by the subject. In further experiments, however, it was found that the subject could draw a key on a piece of paper, and could find a key object in a box, showing that the right hemisphere did see "Key." The important facts to note here are that, first, the subject never seems to "know" that it has seen "Key Ring." Second, the right hemisphere, while seeming to know that it has seen "Key," cannot articulate the fact, and the left hemisphere seems to have seen "Ring" and says so.

It gets even more interesting in further experiments (involving the same key-ring set-up). In one experiment, the subject searched two boxes with various items in them. The left hand searched one box and the right hand searched another box. Both boxes had rings, and keys, and key rings in them. The subject was not allowed to look in the boxes. Each hand was capable of searching the boxes independently of the other. What happened was that the right hand came up with a ring, and the left hand came up with a key. Neither hand came up with a key ring.

The philosophical issue is the following. Something saw "Key" and something saw "Ring," but no thing seems to have seen "Key Ring" (there is no single entity that seems to have had the experience of seeing "Key Ring"). So, under certain conditions, human consciousness seems to be split, or to put it more controversially, in split-brain patients, there seems to be two separate and independent streams of consciousness. There seems to be no one stream of consciousness in which all of the patient's experiences are unified, or "take place."

What do we make of all of this, with respect to human consciousness, in general? First, outside of the experimental conditions, the right and left hemispheres of split-brain patients, do have ways of "experiencing" the same things. For example, the eyes are constantly moving, so that the left and right visual fields are pretty much seeing the same things. Second, in humans who have not had their corpus callosum severed, the left and right hemispheres do communicate. But these experiments have led writers to suggest that human consciousness is not unified. That is, there is no human being whose consciousness is unified--every human being's consciousness is un-unified to some degree. These may not seem like very controversial claims. For any human being, there seem to be situations where they do not notice what would seem to be an obvious part of their perceptual field. For example, someone might be looking right at their car keys on the table, but they do not seem to be seeing the car keys. In general, we don't notice things all of the time. But there is a controversy here, and it has to do with the prevalent model, or theory we have of human consciousness. What I call the prevalent model, the way human beings think about their own consciousness, the way most human beings believe their minds and consciousness to be, and in fact the way most psychological theories view human consciousness and the mind (when those theories have such a view), assumes that human consciousness is unified, under normal conditions.

The general question is this: is human consciousness, under normal conditions, unified by some "thing" in the mind, or some process, such that there is some "place" in the mind where every experience that could be had by a human is experienced by that thing (unless it is not, in which case it is not experienced by any other entity in the mind)? The answer to this question, according to the prevalent theory is, "Yes." However, some writers have suggested that, given the split-brain experiments, the answer should be, "No."

The conflict I am bringing up is not new. Quite a number of writers before me have written about it. I'm going to refer to Derek Parfit's Divided Minds and the Nature of Persons to set the stage here, because he has given names to what I have been calling the prevalent theory and its alternative, and so that we can see what the controversy amounts to in more detail.[5] Here is how Parfit explains what I have called the "prevalent theory:

On the Ego Theory, a person's continued existence cannot be explained except as the continued existence of a particular Ego, or subject of experiences. An Ego Theorist claims that, if we ask what unifies someone's consciousness at any time...the answer is that these [experiences] are ...experiences which are had by me...."[6]

From now on I will use the phrase "Ego Theory," also. In this article, I will not be concerned about the nature of persons. My main focus will be on the claim that, according to this theory, there is some entity that unifies consciousness. Here is how Parfit explains the alternative theory:

The rival view is the Bundle Theory...According to the Bundle Theory, we can't explain either the unity of consciousness at any time, or the unity of a whole life, by referring to a person. Instead we must claim that there are long series of different mental states and events--thoughts, sensations, and the like--each series being what we call one life. Each series is unified by various kinds of causal relation, such as the relations that hold between experiences and later memories of them.[7]

Again, I am not concerned with the nature of persons. Rather, I'm concerned with the idea of the "one subject of experience," or the Ego. Parfit later claims that the Ego is an idle cog in the explanation of the continued existence of persons.[8] I am going to go a bit further and say that the rival theory to the Ego Theory, what I will still call the Bundle Theory, denies the existence of the Ego, or the existence of a single subject of experience. That is, there is no one place where all of a human's experiences are unified; in other words, there is no entity that has the experiences that could be had by a particular human.

Now, there are what one might call "psychological" or "phenomenological" reasons why one might not want to accept the Bundle Theory. For example, it certainly seems to me that there is one thing/person/ego/subject that is having all of the experiences that could be had by me. When I examine my own consciousness, what I seem to discover is that there is one place where "everything is happening." However, I am not going to consider this kind of "phenomenological" consideration, or argue against it. If one wants to examine an argument against this kind of consideration, read David Hume's argument against it, found in A Treatise of Human Nature.[9] What I will to is examine a number of different phenomena of human consciousness and show that the Ego Theory is inadequate to explain them. With respect to the Ego Theory, these phenomena are anomalies that are difficult to explain.

The first anomaly is the split-brain patients themselves.[10] Given the key-ring experiments (and others), it seems that there is no one subject that experiences "Key Ring." "Key Ring" is not unified in one place in consciousness; there seems to be no one ego that has the experience "Key Ring." Moreover, if there were one particular entity, call it the "Ego," where is it located? Is it located solely in the left hemisphere? If so, there seems no reason to suppose that the right hemisphere can direct the left hand to independently perform the task of searching through a box of items. We could suppose that there is really no ego in the right hemisphere, but that the right hemisphere is some kind of automaton or zombie. But in this case, consciousness isn't unified, anyway: even if the right hemisphere has no ego, the supposed ego in the left hemisphere does not experience what the right hemisphere does. We might suppose that there are two egos, one for each hemisphere. But there is a problem in this supposition, as well: in the severing of the corpus callosum, did the ego get severed, too? Where exactly is the ego in the brain?

We could go on with different suppositions, trying to account for what is happening, but the point is that it's very difficult to explain what is going on, if one supposes that the Ego Theory is true. It seems that in giving any explanation to explain a problem, a different problems crops up. On the other hand, if the Bundle Theory is true, then we don't have to give such awkward explanations: the ego does not exist, there is no subject of all experiences, and consciousness was never unified in the first place. We can simply say that in the split-brain cases, consciousness is more dis-unified than in the normal case.

The second anomaly I want to consider is self-deception, and Sigmund Freud's account of how it could occur in a single consciousness.[11] I'm assuming that self-deception has been taken to be a real phenomenon by those who attempt to explain it. Whether or not it is a real phenomenon is irrelevant to the fact that some people have tried to explain it according to the Ego Theory, and these explanations reveal the deficiencies of the Ego Theory.

Self-deception is as follows. First, there is within one mind two beliefs: the belief that X and the belief that not-X. For example, in one mind there is the belief, "I am a good race car driver," and the belief, "I am not a good race car driver." If there were one ego that "had" every belief, then it seems that one ego could not have both of these beliefs simultaneously. It doesn't seem like I can believe that I am a good race car driver and that I am a bad race car driver at the same time. However, it could be the case that I consciously believe that I am a good race car driver, and that I am deceiving myself, because in fact some part of me "knows" that I am a bad race car driver. So, secondly, self-deception involves the fact that one part of a mind believes or know one thing, and another part of the mind knows a contrary thing, but somehow these two parts do not "communicate." One might suppose, naturally, and on the Ego Theory, that some parts of our mind are not known to us. According to Freud's theory, this unknown part is the unconscious. In this theory, the ego is unaware of the contents of the unconscious. One thing to note in passing is that, on Freud's theory, the mind is not unified, since there is a part of the mind unknown to the subject/ego: the unconscious. Consciousness--all of the stuff that one can be consciously aware of--one supposes, is unified; but there are beliefs and experiences that are not accessible to the consciousness or ego. The mind is not unified. But to continue, what prevents the ego from accessing or knowing about these unconscious contents of the mind? How did those contents get into the unconscious in the first place? Was it random? Well, no. According to Freud's theory, all of that stuff in the unconscious is stuff that would be threatening to the ego--it must be kept in the unconscious. Okay, let's ignore the whole "threatening" issue. What's really at issue is how is how all that stuff is kept in the unconscious (when it is--Freud allows for thoughts to emerge from the unconscious, under certain conditions).

In the case of self-deception, there exists two inconsistent beliefs in one mind. One of the beliefs is "known" by the ego, and the other isn't. In order for the whole person to remain in the state of self-deception, the ego must not become aware of the incompatible belief. What mechanism in the mind prevents the ego from discovering this incompatible belief? To put it another way, what part of the mind "knows" that the incompatible belief is, in fact, incompatible with the belief held  by the ego? On Freud's theory, this part, or entity is the censor. The censor knows what beliefs are in conflict (or threatening) to the ego, and "keeps" them in the unconscious. The problem on this account, which was noted by Jean-Paul Sartre, in Being and Nothingness, is that this solution simply pushes the problem onto the censor.[12] The censor now is an entity in the mind that seems to know all of the contents of the mind. It must know what the ego knows in order to know what to keep from the ego, and it knows the contents of the unconscious in order to know what is to be kept from the ego. In terms of the analysis we have been using, the censor is the subject of all experiences--it is what unifies the mind (although consciousness, on the Freudian view is what is known or unified by the ego). There are a number of problems, here. First, the subject of all experiences is the censor, not the ego, so the censor would seem to be the "most important" subject/entity in the mind. Second, there are really two subjects of experience: the ego, which is the subject of conscious experience, and the censor, which is the subject of all experience. Third, the censor is unknown to the ego; it is as if we have another subject/ego ("ego" in the Ego Theory sense, not Freud's) in our minds, unbeknownst to us.

Problems abound, and again it is difficult to explain the phenomenon of self deception according to the Ego Theory view without raising new problems. The phenomenon of self deception is an anomaly for the Ego Theory. But we can see a pattern here. According to the Ego Theory, for every independent stream of mental events (the left and right hemispheres of the brain), or every independent set of mental events (the conscious and the unconscious), there is posited an ego, or some entity, that is the subject of those events/experiences, and somehow unifies the stream or set. The more streams/sets that are independent in one mind, the more egos must be posited. We have a proliferation of egos. And when we try to "adjust" the theory to account for new anomalies, different problems arise.

Let us next consider a third phenomenon, that of multiple personalities (Dissociative Identity Disorder). The current thinking is that people with this disorder aren't viewed as having distinct personalities, but rather have different states. These different "states" might be thought of as different ways of the person being themselves, or as ways of behaving that are different enough to warrant the claim, from an outsider's perspective that the two "ways" constitute different sets of personality attributes. The difference here is more than the fact that one might, for example, act differently when one is with one's parents from when one is with a party with one's friends. It is often the case that for people with DID that they forget what they did while in a certain state. Although some DID patients report that it feels as if they have within their mind two (or more) of these personality states, we again don't want to focus on this phenomenological aspect. Instead, let us focus on the Ego Theory explanation of the phenomenon. Take the case of a person with personality state A and personality state B. Suppose that personality state A cannot remember what personality state B did last night at the local bar. If there really were an ego (an entity) in the mind at the time of the "non-remembering" this ego is not unifying consciousness and is not the subject of every experience in the mind: there is a whole set of experiences related to personality state B this ego is not aware of. In addition, there was some thing that controlled the behaviors of whatever "person" was in the bar last night, and this thing was not the ego of personality state A. We have again, it seems, two egos. Ego A controls the behavior in personality state A, is aware of the experiences during personality state A, and does not "know" about the experiences had during personality state B. Mutatis mutandis for Ego B.

We see again the same difficulties for the Ego Theory. With the Bundle Theory, however, there are no such difficulties. There is no ego, no single subject of experiences, no entity that unifies the mind. Personality state A and personality state B are two independent causal streams of consciousness. They can operate independently without either "knowing" about the other. On the other hand, there could be times when these separate chains of causal events interact to some degree, in which case they could "know" about one another to some degree. The DID case is just the split-brain case to a lesser degree of disconnectedness, as is the case of self-deception. In fact, every phenomena of human consciousness is the same case: the streams of consciousness in a human mind are connected to greater or lesser degrees, depending on the state of the mind. And we mean every phenomena. The fact that you can drive from one place to another and remember the conversation you had with your passenger, but nothing about the drive itself is explained in the same way: there are different streams of consciousness operating more or less independently.

This is the main virtue of the Bundle Theory. Every phenomenon of the human mind, or human behavior has an explanation based on the same assumption that there are independent streams of consciousness in the mind. Notice that the Ego Theory does not have this virtue. In a "normal" human there is one ego/subject, whereas in the anomalous cases, two or more are posited.

So, the Bundle Theory is a better theory, because the anomalies can be explained (that is, there are no anomalies), and the theory does not need to posit more and more entities to cover anomalous cases. For these reasons alone the Bundle Theory should be accepted as the most accurate theory about the human mind. So why hasn't it been accepted, given the fifty years of writing about split-brains, and the literature about this new theory (whatever one wishes to call it)? I would suggest that, unlike other revolutionary theories, it's more difficult to accept that our minds are like that when it seems, from our own introspection of our minds, that we are not like that. I would also suggest that the explanatory language necessary to help us understand this theory has not developed sufficiently.

It's unclear that the Bundle Theory will ever replace the Ego Theory, in spite of the former's virtues. But let's look at how superior theories replace less superior ones, in terms of Thomas Kuhn's analysis in The Structure of Scientific Revolutions.[13] As a reference for our thinking, we will compare the Ptolemaic theory of the movement of heavenly bodies, the geocentric model of the solar system, with the Copernican theory, the heliocentric model.

On the Ptolemaic theory, the earth is the center of the universe, and all heavenly bodies revolve around the earth. In fact this is the way things appear to us on earth: all of the heavenly bodies are orbiting above us. If the Ptolemaic theory is the case, then all of those bodies should always move from the east horizon to the west horizon. The problem for the theory is that, once observational equipment became sophisticated enough, some people observed that some bodies either stopped moving or moved from west to east--in a retrograde motion. These phenomena are anomalies, in Kuhn's terms, for the normal science practiced at that time--that is, science as practiced under what he calls a paradigm. We can think of this paradigm as the Ptolemaic theory. The practitioners of the astronomy of the time attempted to modify the theory--adjust it here and there--to account for the anomalies, but eventually a "better" theory came along, the Copernican theory, which could more easily explain the anomalies. On the new theory, if we assumed that the earth was not the center of the solar system, but that the sun was, and also that the sun was not the center of the universe, the anomalies of the Ptolemaic system were not anomalies of the Copernican system.

Kuhn is concerned with how scientific revolutions happen: how is it that one theory replaces another? This is partly an historical question, but one can see in Kuhn's writings that there is a pattern in these historical replacements. Generally speaking, the pattern is that the fact that one theory is inadequate to explain anomalies is revealed by the paradigm itself, and another theory is then proposed and in this theory the phenomena observed are no longer anomalies.

This is the situation we have with respect to the Ego Theory and the Bundle Theory. Under the paradigm of the Ego Theory, there occur certain anomalies, and if we were to adopt another paradigm, the Bundle Theory, these phenomena would no longer be anomalies. So, why hasn't the Bundle Theory replaced the Ego Theory?

Kuhn reviews the process from when a new paradigm takes over and the normal science associated with that paradigm ensues. He says that at the start, when the new paradigm begins to replace the old, it's more like a promise of success. It's like saying: "Look if we think about the problem this new way we can solve these few problems [explain some phenomena that couldn't be explained under the other theory], and maybe we can solve these other problems we've been wondering about." At some point, the new paradigm is accepted, and then there ensues what he calls "mop up" work. More scientists use the new paradigm and begin studies and experiments that show that data and phenomena that were unusual can now be explained. Historically, then, it's unclear that we are at the point of time where the new paradigm has been accepted in the larger scientific community. I would argue that most researchers, and the writers basing their articles on the research done by them still believe the Ego Theory, at least as an unconscious assumption about the way their minds are. After all, it does introspectively seem to us that we are the subject of experience and this subject unifies our consciousness.

In the Copernican versus Ptolemaic case, what we observe in the heavens does not change once we adopt the new Copernican paradigm. The heavens don't change, and we see what was always available to see. What has changed is the way we imagine the heavens. That is, the imaginary picture we create in our minds to model the heavens is different, and we can compare the differences. I think that in the Ego versus Bundle case, the situation for us is different. I can easily create a picture in my mind that models the case of the Ego Theory. What is more, introspectively, this is the way it seems to me; that is, the personal observable data I have (analogous to my observation of the heavens) suggest to me that there is this subject of experience. The Ego Theory as a model matches my introspective observations. On the other hand, with respect to the Bundle Theory, 1) it's not clear to me what picture I should create that models the theory, and 2) all the introspective data I have about my own mind suggests that what is going on in there is not a series of more or less disconnected mental events--my consciousness, to me, does seem unified.

Now, I, personally, accept the Bundle Theory as true, for the reasons noted, among others. However, the question is why it is not accepted as the new paradigm of the human mind. I think the problem is with the issues 1) and 2). Issue 1) has to do with my suggestion that the explanatory language necessary to help us understand this theory has not developed sufficiently. To put it simply: someone needs to come up with a simple way of explaining the Bundle Theory so we can "picture" it in our mind. I think what needs to happen here is for researchers of the nature of the brain to seriously begin to explain the phenomena of consciousness, the brain, and behavior explicitly in terms of this theory. I'm supposing that during the Copernican revolution people might have asked, "Why does that star appear to move backward in the sky?," and the explanation of this, in terms of the Copernican theory, might have helped them model the theory in their minds. The more explanations that were given, the easier it may have been to mentally model the theory. Similarly, if researchers now make more of an attempt to explain humans in terms of the Bundle Theory, the easier it will be for us to imagine it.

Issue 2) is more difficult. When I look into the workings of my own consciousness, it seems to me that there is a subject that has experiences. Whether or not this subject has access to all the contents of the mind, or unifies the mind is unknown to me (the subject); however, it seems irrefutable that there is this subject that has the experiences. Issue 2) may be insurmountable to us. This "raw data" that I have about the phenomenology of my own mind is not public; I cannot compare this data directly with anyone else, as the raw data of the heavens can be shared between people. No one else can look into my mind and point out to me that some feature I perceive should be imagined or modeled in some other way than I introspectively perceive it to be.

The raw data in my mind seems to necessarily suggest that I am a subject of experiences. Hume, however, seems to have had a different experience of his own consciousness:

For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception. When my perceptions are removed for any time, as by sound sleep; so long am I insensible of myself, and may truly be said not to exist. And were all my perceptions removed by death, and coued I neither think, nor feel, nor see, nor love, nor hate after the dissolution of my body, I should be entirely annihilated, nor do I conceive what is farther requisite to make me a perfect non-entity. If any one, upon serious and unprejudiced reflection thinks he has a different notion of himself, I must confess I call reason no longer with him. All I can allow him is, that he may be in the right as well as I, and that we are essentially different in this particular. He may, perhaps, perceive something simple and continued, which he calls himself; though I am certain there is no such principle in me.[14]

We can never observe this "self" or subject that has experiences. For Hume, that meant that it didn't exist. On the other hand, the experiences seem to be projected onto some subject. It seems impossible for this subject to perceive itself as an experience; it would be like trying to turn one's self around (really quickly) in one's mind to catch a glimpse of the thing that does the experiencing--as if a movie screen could see itself. So, even if I intellectually accept the Bundle Theory as true, it would be nice if someone could explain to me how it seems to me that there is a subject having experiences, when there is really not. I could then psychologically accept the Bundle Theory.