Two brains—my life in science
DOI:10.1093/acprof:oso/9780199228768.003.0009
Abstract and Keywords
This chapter looks at developments in the split-brain studies during the past fifty years from a personal perspective. It describes experiments in split-brain research and the discovery of the effects of callosal disconnection. It highlights major findings in split-brain research that relate to the problem of consciousness and suggests that it is important to understand that the problem is constantly evolving and new dimensions are continually presenting themselves.
Understanding anything large comes from understanding one aspect of that thing in the greatest possible detail and with the greatest possible clarity. In my case, my study of cognitive neuroscience has been enabled by a life's work on a particular topic—studying subjects whose brains have been split into two parts. During almost a half century of working with such patients, I have come to realize that scientific stories are never as they first appear. New combinations of scientific personalities, experimental opportunities, and empirical data cause both questions and answers to be revised and expanded, seemingly in perpetuity. And that, of course, is as it should be; scientists are paid to doubt, to challenge, and to reassess. I suppose good lawyers are paid to do the same, but the difference is that they must be partisan, whereas science is concerned with what is true for everyone, not what is beneficial for just one person. That is what makes a life in science so fulfilling.
Forty-six years ago, I examined a robust and charming man, WJ, who was about to undergo cerebral commissurotomy, the so-called split-brain surgery, to control his otherwise capricious epilepsy. He was the sort of level-headed person to instil respect in a young, green, graduate student like myself. I had just started graduate school at Caltech under the direction of Professor Roger W. Sperry. Dr Joseph Bogen, a resident at the time, had critically reviewed the medical literature and was convinced that split-brain surgery would have beneficial effects. Dr P. J. Vogel, a professor of neurosurgery at the Los Angeles-based Loma Linda Medical School, performed the surgery, and my chore was to quantify the psychological and neurological changes, if any, in the way WJ behaved once the connections between his hemispheres had been sectioned. The conventional wisdom suggested that nothing would happen. Several studies by a gifted young neurologist at the University of Rochester, A. J. Akelaitis, twenty years earlier had found that callosal section in human subjects produced no behavioural or cognitive shifts. Karl Lashley had seized on this finding to push his idea of mass action and ‘equipotentiality’ of the cerebral cortex; discrete circuits of the brain were not important, he claimed—only cortical mass. (p.104) After all, he concluded, cutting the massive nerve bundle that connected together the two halves of the brain appeared to have no effect on interhemispheric transfer of information.
I learned about the split-brain world as a young undergraduate summer fellow at Caltech the summer between my junior and senior year. Inspired by the excitement of the ongoing animal research on split-brain cats and monkeys, I returned to Dartmouth College determined to go to graduate school at Caltech. Although my summer project was focused on trying to anaesthetize a half-brain of a rabbit I couldn't help but become captivated by the question of what would happen to humans with callosal sections. During my senior year at Dartmouth I had the idea to try to retest those Aklaitis' patients in nearby Rochester, New York, during my spring break. I designed many experiments and exchanged letters with Sperry about the ideas and the plan. I applied to the Mary Hitchcock Foundation at Dartmouth Medical School and received a small grant to rent a car and to pay for my stay in Rochester.
In the end I didn't see the Rochester patients, even though my car was loaded with borrowed taschistoscopes from the Dartmouth psychology department. The effort to reveal the effects of callosal disconnection in humans would come later. As soon as I arrived at Caltech, for my first day of graduate work, the assignment was given to me by Sperry. The split-brain experiments I had designed during my senior year at Dartmouth would finally be implemented, but on Caltech patients rather than Rochester patients. Nothing can possibly replace a singular memory of mine: the moment when I discovered that WJ could no longer verbally describe, using his left hemisphere, stimuli presented to his freshly disconnected right hemisphere. An experiment I had designed, executed, and carried out as a mere graduate student at Caltech had worked. With it the modern human split-brain story began and I spent the next five years in a sort of sublime state, working every day at the finest scientific institution in the world with one of the greatest biologists of all time, Roger Sperry.
These electrifying beginnings of the human work might have been predicted by dozens of experiments on animals. Study after study had shown that corpus callosum section profoundly altered brain function in cats, monkeys, and chimpanzees. Specifically, information presented to one brain hemisphere remained isolated in that hemisphere. It was as if dividing the great cerebral commissure produced an animal with two minds, neither of which was aware of the workings of the other. Ronald E. Myers and Sperry had already coined the term ‘split brain’ to describe such animals. Yet, the idea that callosal section would produce a similar condition in humans seemed bizarre.
(p.105) Preoperatively, WJ could name stimuli presented to either visual field or placed in either hand. With his eyes closed, he could understand any command and carry it out with either hand—in short, he was entirely normal. The stage was ideally set to investigate what would happen following the disconnection of his cerebral hemispheres. The scientific context and the time were right for us to ask the right questions: Could it be that a disconnected right hemisphere was as conscious as a disconnected left hemisphere? Could it be that a state of co-consciousness could be produced in a human being? Where would positive answers to either or both of those enquiries lead us?
When WJ returned for testing after surgery, I experienced, as I said, one of those pivotal moments in life. First, and to no one's surprise, the subject normally named and described stimuli that were presented to his left hemisphere. Then came the critical test: what would happen when information was flashed to his verbally silent and physically isolated right hemisphere? Akelaitis' work predicted that the subject would describe the stimulus normally, as his studies suggested that the corpus callosum played no essential role in the interhemispheric integration of cerebral information. On the other hand, the animal work suggested that something interesting might emerge. As it happened, something interesting did emerge: the idea that splitting the human brain produced two separate conscious systems. It was a revolutionary idea, and over forty years later it is one that still needs study and clarification.
It is curious that, despite centuries of study and speculation about consciousness, there is no general agreement even about what the term means. If you asked twenty students of the problem to finish the sentence, ‘Consciousness is…’, twenty different definitions would result. Still, most of us would agree that the term refers to that subjective state we all possess when awake and to our feelings about our mental capacities and functions. As is typical with vast and ill-defined concepts, it is easy to offer simple examples of what it means to be conscious, but, at the same time, lifetimes of inquiry will not divulge the entirety of its nature.
When the first split-brain patients were studied we avoided confronting the essential definitional question in favour of measuring the separate capacities of each half-brain. Following my initial encounter with WJ, I have spent the last forty-six years trying to characterize the nature of conscious mechanisms in these patients. I have attempted here to track the major findings in split-brain research that relate to the problem of consciousness. Clearly our understanding of the problem is constantly evolving and new dimensions continually present themselves. I should say from the start that the gift of launching these studies with Roger Sperry at Caltech and the continuing (p.106) capacity to study other patients like WJ with dozens of other students and colleagues has been a joy.
The first decade: basic principles
True to our expectations, and like all right-handed split-brain cases that followed, WJ normally named and described information presented to his left speaking hemisphere. What was surprising was his seeming lack of response to stimuli presented to his surgically isolated right hemisphere—it initially seemed as though he was blind to stimuli presented to the left visual field. To investigate this idiosyncrasy further, I devised a series of tests that allowed WJ to respond to visual stimuli using a reaction-time Morse code key with his left hand (controlled by his right hemisphere) rather than verbally (using his speaking left hemisphere). I flashed a light, and WJ said he didn't see anything, even though his left hand responded to the stimulus by pressing on the key!
An early conclusion from these results was that, following callosal section, each brain hemisphere behaved entirely independently of the other. Information experienced by one side seemed unavailable to the other and, moreover, each half-brain seemed specialized for particular kinds of mental activity. The left was superior in terms of language ability, whereas the right seemed more able to carry out visuospatial tasks. Hemispherical separation had isolated two structures with distinct and complex functions. The capacities demonstrated by the left hemisphere came as no surprise. However, when the first experiments showed that split-brain patients were able to read using the right hemisphere and to use the information thus gained as the basis for decisions, the case for a double conscious system seemed strong indeed. We could even elicit emotional responses from the right hemisphere. Dozens of studies that I carried out on split-brain patients during the following five years confirmed this dramatic state of affairs. After separating the human cerebral hemispheres each half-brain seemed to work and function outside the conscious realm of the other. Each could independently learn, remember, emote, and carry out planned activities.
Although these findings were dramatic, they posed even more questions than they answered about the essential nature of dual consciousness. Splitting the brain into two consciousnesses presented us with two systems that we didn't understand, instead of the single cryptic system we had started with. At this point, the field was too new to have developed depth by pushing the upper limits of right-hemisphere mental capacities, nor had it developed sufficient breadth, by examining a large enough pool of patients, to reveal the rich variation in right hemisphere capacities that has since been discovered. (p.107) Most importantly, however, the challenge to define consciousness itself lingered in the backs of all our minds, as yet we hadn't addressed it.
The second decade: origins of modular concepts and the interpreter
By the 1970s, the passage of time had provided more studies and more patients, and the original nature of split-brain studies had been modified substantially. The field had drifted into thinking about different kinds of consciousness, and the notion that mind left dealt with the world differently than mind right was the major conclusion of studies during this era. Though interesting in its own right, this characterization of how each hemisphere processes information still begged the question of what consciousness actually was and how the brain enabled it to be experienced.
In many ways, the work in the early 1970s was misleading. Reports with chimaeric stimuli found that split-brain patients favour the right hemisphere for ‘gestalt’ stimuli and the left hemisphere for ‘analytical tasks’, and our hypotheses briefly took on a new direction. We began to argue that it wasn't so much that there were separate conscious systems following commissure section but simply that each hemisphere possessed a different cognitive style. This characterization was short lived in the scientific community, but has been annoyingly persistent in the popular press. The paper that triggered this trend in left brain/right brain thinking used stimuli that were already well known to elicit preferred hemisphere functioning. Demonstrating through another stimulus preparation medium that the left hemisphere preferred language-based stimuli and the right hemisphere preferred faces merely replicated existing results and was a distraction from new research.
During the mid-1970s, a number of reports emphasized an additional feature of right hemisphere specialization. Milner and Taylor reported superior performance in the right hemisphere on non-verbal tactile stimuli. Joseph LeDoux and I found the manipulations of a stimulus to be critical in bringing out right hemispheric superiorities. For example right hemispheric superiority was only revealed in a block design test in which the patient manipulated the blocks to make the patterns required; in an equivalent, “match to sample” test in which patterns were only visually inspected right superiority disappeared. While these new observations were challenging enough to the simple view of hemispheric functioning and to ideas about dual consciousness, the new conceptual framework was even more antithetical to existing concepts about the unity of conscious experience. In brief, the new view suggested that the brain was organized in a modular fashion with multiple (p.108) subsystems active at all levels of the nervous system, and that each subsystem could process data outside the realm of conscious awareness. These modular systems were fully capable of producing behaviours, mood changes, and cognitive activity. Such activities were in turn monitored and collated by a special system in the left hemisphere that Ledoux and I called the ‘interpreter’.
We first revealed the interpreter using a simultaneous concept test. In this type of test, the subject is shown two pictures—one exclusively to the left hemisphere and one exclusively to the right. The subject is then asked to choose pictures that are associated with those lateralized images from an array of pictures placed in full view in front of them. For example, a picture of a chicken claw is flashed to the right visual field, and a picture of a snow scene to the left visual field. Of the pictures placed in front of the subject, the obviously correct association is a chicken for the chicken claw and a snow shovel for the snow scene.
Accordingly, subject PS responded by choosing the chicken picture with his right hand and the snow-shovel picture with his left. The left brain hemisphere, however, was aware only of the chicken-claw image, while the right hemisphere was aware only of the snow-scene image. When asked why he chose these items, his speaking left hemisphere replied, ‘Oh, that's simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.’ The left brain, observing the left hand's response, interpreted that response only in the context of its own sphere of knowledge—a sphere that did not include information about the left visual field snow scene.
In a related experiment, we lateralized written commands by presenting them tachistoscopically to the subject's left visual field. In an example where the command was ‘laugh’, the patient laughed and, when asked why, replied, ‘You guys come up and test us every month. What a way to make a living!’. If the command ‘walk’ was flashed to the right hemisphere, the patient would stand up from their chair and start to leave the testing van. When asked where they were going, the left brain might say, ‘I'm going into the house to get a cola.’ Again, the left hemisphere observes and interprets the actions of the isolated right hemisphere in order to create a verbal response.
Over the past several years my search for corroborative evidence has taken me to the neurosurgical wards of New York Hospital, where a procedure called angiography is carried out routinely on patients about to undergo brain surgery. A long catheter is fed up one of the main arteries that supply the brain from an entry point on the leg, and a radio-opaque dye is injected that flows through either the left or right half-brain. X-ray pictures are taken at that precise moment, and abnormalities in the arterial system are thereby revealed to (p.109) the surgeon. It turns out that while the catheter is in position for this procedure it is frequently advisable to determine whether or not the hemisphere about to undergo surgery is dominant for language and speech. The Wada test, as the procedure is known, is performed by injecting anaesthetic through the catheter, and for approximately two minutes, one side of the brain falls asleep while the other remains alert. Most frequently it is the left, language-dominant, hemisphere that must be tested.
My idea was to give the right hemisphere something to remember while the left hemisphere was asleep. Then, after the left brain woke up, I would ask it whether or not it knew about the information I had given to the right. What we discovered was that if we allowed a non-verbal response of which the nonverbal right hemisphere is capable, such as pointing to make a choice between stimuli, the correct decision was always made. If we required a verbal response, the patient was incapable of supplying it. Therefore, even in normal patients, it is possible for right-hemisphere information to be encoded in such a way that it cannot be accessed by the left hemisphere's language system.
At this point, our research had shown that there are many ways to influence the left brain interpreter, and we were still interested in determining whether emotional states present in one brain hemisphere would have an effect on the affective tone of the other hemisphere. It was at this point that we met VP, a dazzling 28-year-old woman with a keen sense of life who was a patient of Dr Mark Rayport of the Medical College of Ohio. She is introspective about her medical history and articulate in expressing her feelings. When we first met her, her right hemisphere skills were limited to simple writing of answers and the capacity to carry out verbal commands. Flash the command ‘smile’ to her right hemisphere and VP could do it. Ask her why she was smiling and her left hemisphere would concoct an answer.
But two years later, VP's right hemisphere could directly tell us why, because by then it had developed the capacity to talk. During the time when only her left brain could speak, however, we were able to set up mood states in her non-talking hemisphere and study whether or not the talking hemisphere was aware of the mood, and, if so, how it dealt with the induced mood. From all of the other studies, of course, it was clear that the left brain was not directly knowledgeable about the actual pictures or movies that had been shown to the right brain. But could it detect the mood?
Using a very elaborate optical computer system that detects the slightest movement of the eyes, we were able to project a movie exclusively to the left visual field. If the patient tried to cheat and move her right eye toward the movie image, the projector was automatically shut off. The movie her right hemisphere saw was about a vicious man pushing another man off a balcony (p.110) and then throwing a fire bomb on top of him. It then showed other men trying to put out the fire. When VP was first tested on this problem, she could not access speech from her right hemisphere. When asked about what she had seen, she said, ‘I don't really know what I saw. I think just a white flash.’ I asked, ‘Were there people in it?’ VP replied, ‘I don't think so. Maybe just some trees, red trees like in the fall.’ I asked, ‘Did it make you feel any emotion?’ VP: ‘I don't really know why, but I'm kind of scared. I feel jumpy. I think maybe I don't like this room, or maybe it's you, you're getting me nervous.’ Then VP turned to one of the research assistants and said, ‘I know I like Dr Gazzaniga, but right now I'm scared of him for some reason.’
This experimental evidence merely illustrates a rather extreme case of a phenomenon that commonly occurs to all of us. Our mental systems set up a mood that alters the general physiology of the brain. In response, the verbal system notes the mood and attributes cause to the feeling based on available evidence. Once this powerful mechanism is clearly demonstrated, given the complexity of real-life emotional stimuli, one cannot help but wonder how often we are victims of spurious emotional/cognitive correlations.
Although our split-brain subjects always possess at least some understanding of their surgery, they never say things like, ‘Well, I chose this because I have a split brain and the information went to the right, non-verbal hemisphere.’ Even patients who have exceptional IQs tend to view their responses as behaviours emanating from their own volitional selves. As a result, they incorporate those behaviours into theories to explain why they behave as they do. One can imagine that, at some point, a patient might be studied who might choose not to interpret such behaviours because of an overlying psychological structure that prevented the response. Or one can imagine a patient learning by rote what a ‘split brain’ is all about and why, therefore, a certain behaviour most likely occurred. Such a circumstance would certainly complicate the role of the researcher, and such subjects might well not be able to offer explanations for their behaviours.
There are occasions when a patient who is having trouble controlling his or her left arm due to a transient state of dyspraxia will tend to dismiss anything that he or she does under the direction of the right brain. This makes the simultaneous concept test inappropriate. In such situations, a single set of pictures is presented and only one hand is allowed to make the response. For example, the word ‘pink’ is flashed to the right hemisphere and the word ‘bottle’ to the left. Placed in front of the subject are pictures of at least ten bottles of different colours and shapes, and the subject is required to respond using the right hand.
(p.111) When this test was run on split-brain subject JW, on a particular day when he said that he could not control his left hand, he immediately pointed to the pink bottle with the right hand. When asked why he had done this, JW said, ‘Pink is a nice colour.’ In this case, JW responded to a stimulus that had been presented to his right hemisphere using his right hand, in defiance of our expectation that he would be unable to do so. When he was pressed to explain how he had done it, his left-hemisphere speech apparatus was unable to provide an explanation, and so the interpreter responded as best it could, claiming that the subject had made a simple aesthetic choice.
It has been well established that the human brain follows a modular organization, and that those ‘modules’ do manifest themselves through function-specific physical regions of the brain. The precise nature of the neural networks that carry out those functions is less clear, however. What is apparent is that they operate largely outside the realm of awareness, and that they announce their computational products to various executive systems that result in behaviour or cognitive states. Managing and interpreting all of this constant and parallel activity is the role of the left hemisphere's interpreter module.
The interpreter is of primary importance to our identity as human beings; it is what allows for the formation of beliefs, which in turn yield mental constructs that allow us to do more than simply respond to stimuli. It does not appear, however, to be the system that articulates the content of consciousness—it does not generate feelings about our thoughts. I have much more to say about this property of the left hemisphere below.
The third decade: variations in patterns
In the 1980s, reports of more split-brain cases made it possible to begin to study the degrees and types of variation among subjects, particularly with regard to hemisphere specialization patterns. What was striking in these new studies was that the patients all reported that they felt mentally unchanged from their preoperative state. In other words, although their surgery had caused brain function to be redistributed in various ways, they all held in common the notion that their consciousnesses had not changed significantly.
There was also increasing interest during the 1980s in the possible role of subcortical processes in unconscious brain activity. Some studies tried to demonstrate that the split-brain human was not, in fact, so very ‘split’ at all—that common subcortical mechanisms integrate high-level information between the hemispheres, independent of the corpus callosum.
(p.112) The effort to integrate all of these strands of research helps to define a set of issues that must be resolved as part of the attempt to reach a functional definition of consciousness per se. It is necessary to determine whether or not there are actual structural differences in how each individual brain processes information. Equally important is to examine more closely how variations in cortical organization may impact on demonstrable aspects of personal consciousness. Finally, the possible role of subcortical systems in unconscious mechanisms must be examined.
It has always been difficult to quantify the costs to cognitive ability incurred by callosal section. Early studies showed no changes in reaction time, ability to perform simple discriminations, verbal IQ, or capacity to form hypotheses. There have since been some reports that negative effects can be registered on memory function, although other studies have disputed this. Some studies have shown that hemispheric disconnection actually provides for supernormal capacity to apprehend perceptual information by allowing each half-brain to function without perceptual interference from the other. In short, various modes of research are challenging the original view that each half-brain is a functioning, independent system, the functioning of which is relatively unaffected by callosal section. The old view was based on the behavioural profiles of split-brain subjects who possessed language in each hemisphere. In that small group of subjects, each hemisphere seemed capable of responding in its own way to a wide variety of stimuli.
Cases where post-callosotomy right-hemisphere verbal performance is poor to non-existent raise the question of whether right-hemisphere verbal skills are entirely absent, or whether they are merely unable to manifest themselves after disconnection from the dominant left hemisphere. That possibility has led to the hypothesis that such patients possess the perceptual capacity and engrams necessary to generate speech, but lack the capacity to operate on them. Prior to split-brain surgery, EB performed a number of tests, including the nonsense wire figure test of Milner and Taylor. She was able to perform this task, which is designed to tap into right-hemisphere specialized systems, with either hand when the objects were presented out of view. Her intact callosum, it would appear, assisted in distributing information from her left brain over to the specialized system in the right hemisphere. At least, that is how we have come to think about these kinds of results.
After the posterior half of the corpus callosum had been cut EB was unable to name objects placed in her left hand in typical split-brain fashion. The fibres crucial for the interhemispheric transfer of tactile information had been severed, and, as a result, what the right hemisphere knew the left knew not. EB also proved to lack right-hemisphere language capability. Although she was (p.113) able to find points of stimulation on her left hand by touching them with her left thumb, thereby demonstrating good right-hemisphere cortical somatosensory function, she was unable to retrieve an object named by the examiner with her left hand. Such a task would be easily managed by a patient with right-hemisphere language capability. Most importantly, however, EB could no longer perform the wire figure task with either hand.
As EB could perform the task before but not after surgery, it is clear that her right hemisphere possessed a specific capacity when it was connected to the left that it lacked once it had been disconnected. As we have noted, findings of this nature suggest that the left brain may normally contribute certain executive functions to specialized systems in the right brain. The capacity to carry out such non-verbal tasks, which was thought to be the product of one integrated system, is actually dependent upon the interaction of at least two systems, each of which is located in a different brain area.
The evidence to date suggests that there are separable factors active in what at first appear to be unified mental activities. One must envision that something on the order of executive controllers are active in manipulating the data of specialized processing systems. These controllers normally tend to be lateralized in the left brain, and when the right brain becomes isolated from their influence the specific functions of the right brain become hard to detect by testing the right hemisphere alone. Yet the impact of all of the newly discovered variation in left-hemisphere organization on the patient's own sense of consciousness following split-brain surgery is virtually nil. If consciousness reflects the felt state about specialized capacities, a neural system can be aware of only those capacities it possesses—it cannot sense the absence of a cognitive feature that it lacks. Observations such as these have led me to the conclusion that consciousness is not learned, and is best thought of as an intrinsic property of a neural network.
The fourth decade: establishing the evolutionary context
It was not until late in the 1980s that I became convinced that our understanding of consciousness is best enabled by placing the phenomenon in an evolutionary perspective. That context causes certain truths to emerge for me that give rise to the idea that, at its core, human consciousness is a feeling about specialized capacities. Throughout the development of split-brain research, one salient fact has remained: disconnecting the two cerebral hemispheres, while eliminating direct interaction between the halves of the cortex, does not typically disrupt cognitive and verbal intelligence.
(p.114) The left hemisphere remains the dominant cognitive entity following such surgery, and this dominance seems to be sustained not by the entire cortex, but by specialized circuits within the left hemisphere. In short, the unique properties of the inordinately large human brain are engendered by its circuitry, not simply by its inordinate size. It is the accumulation of specialized brain circuits, then, that accounts for the human conscious experience. Furthermore, our sense of being conscious never changes during the normal ageing process. Taken together, these two views lead to the conclusion that what we refer to as ‘consciousness’ is nothing more or less than a collection of feelings that we have about our specialized capacities. We have feelings about people and objects we interact with, and about our capacities to think, to believe, and to use language.
In other words, consciousness is not a distinct system—it reflects the affective component of specialized systems that have evolved to enable human cognitive processes. Combined with the human inferential system, which seems to be limited to the left hemisphere, it empowers all sorts of mental activity. Our consciousness of those mental activities depends on our capacity to assign feelings to them, and that is what distinguishes human consciousness from everything else, including the electronic artefacts with which we surround ourselves.
Naturally, viewing consciousness as a myriad of feelings about specialized abilities predicts that the consciousness emanating from one hemisphere would differ radically from that emanating from the other. Whereas left-hemisphere consciousness would reflect what we refer to as normal conscious experience, right-hemisphere consciousness would vary as a function of the specialized circuitry that half-brain possesses. Mind left, with its complex cognitive machinery, can distinguish between the states of sorrow and pity, for instance, and it appreciates the feelings associated with each state. The right hemisphere does not possess the cognitive apparatus to create such distinctions and, as a consequence, its state of self-awareness is relatively low. Specific types of reduced right-hemisphere capacity, therefore, have specific implications for the states of consciousness of the subjects in which they are found.
Patients with a split brain without right-hemisphere language capability exhibit a limited capacity to respond to patterned stimuli that ranges from no capacity at all to the ability to make simple matching judgements at above-chance levels of performance. Patients who possess the capacity to make perceptual judgements that do not involve language do not exhibit the ability to make a simple same/different judgement within the right brain when both stimuli are lateralized simultaneously. In other words, when two simultaneously (p.115)presented figures required the judgement ‘same’, the right hemisphere failed. This profile is commonly seen in all kinds of patient with a silent right hemisphere, and it seems to be independent of overall subject intelligence.
This minimal-capacity profile stands in marked contrast to that of patients who possess right-hemisphere language. The right brain of these patients is responsive, and their overall capacity to respond to both language and non-language stimuli has been well catalogued and reported. In the East Coast series of patients we study, this observation includes the case of JW, whose right hemisphere has understood language and has had a rich lexicon throughout our association with him, as assessed by the Peabody Picture Vocabulary Test and other specialized tests. Until recently, however, JW could not generate speech from his right hemisphere. Studies with VP and PS revealed that these patients were able to understand language and to speak from either half-brain. It would be reasonable to suppose that this extra skill would add to their right-brain capacities to think, which is to say to interpret the events of the world.
It turns out, however, that the right hemispheres of both patient groups are poor at making simple inferences. The subjects were tested by being asked semantically to combine the content of two pictures that were presented one after the other to their left visual fields. Presented with a picture of a match and then a picture of a woodpile, for example, neither group was successful in deducing that a burning woodpile was the correct result. In another test, simple words were presented one after another to the subject's left visual field, and the subject was instructed to choose the word that reflected the causal relationship between them from a list of six possible answers. The subjects also failed these trials, a typical one of which might consist of the words ‘pin’ and ‘finger’ being flashed to the right brain, the correct answer being ‘bleed’. Although the right hemisphere could always find a close lexical associate of a word that was given by itself, it could not perform the interpretive function necessary to recognize relationships between two words.
In this light, it is hard to imagine that the left and right hemispheres have similar conscious experiences. The right cannot make inferences and, as a consequence, is extremely limited in what it can have feelings about. The left hemisphere, on the other hand, constantly and almost reflexively labels stimuli, making causal inferences and carrying out a host of other cognitive activities. Recent studies have shown that the left brain carries out visual search tasks in a methodical manner, whereas the right hemisphere tends to perform haphazardly. The evidence surrounds us that the left hemisphere is predisposed to analyse and differentiate the workings of the world, whereas the right hemisphere simply monitors its surroundings.
(p.116) The fifth decade: it never ends
I was recently asked by a Time Magazine reporter: ‘If we could build a robot or an android that duplicated the processes behind human consciousness, would it actually be conscious?’. It is a provocative question and it is one that persists, especially as one tries to capture the differences between the spheres of consciousness that exist between separated left and right brains. Much of what I have written here has appeared before in other forums and, for students of split-brain research, is not all that new. Yet, I find the way we all nuance our understanding of complex topics to be ever changing, as none of us holds the true answers in our hip pocket. I found myself answering the reporter with what I feel is a new twist.
Underlying this question is the assumption that consciousness reflects some kind of process that brings all of our zillions of thoughts into a special energy and reality called personal or phenomenal consciousness. That is not how it works. Consciousness is an emergent property and not a process in and of itself. It is the taste of salt that is the emergent and unpredictable product of sodium and chloride coming together. Our cognitive capacities, memories, dreams, etc. reflect distributed processes throughout the brain and each of those entities produces its own emergent state of consciousness. Consider one fact. A human split-brain patient who has had the two halves of her brain disconnected from one another does not find that one side of the brain misses the other. Her left brain has lost all consciousness about the mental processes managed by her right brain, and vice versa. This is just as with ageing or with focal neurological disease. We don't miss what we no longer have access to. The emergent conscious state arises out of each capacity. If they are disconnected or damaged, there is no underlying circuitry from which the emergent property arises.
The thousands, if not millions, of conscious moments that we experience each reflect one of our networks being ‘up for duty’. When it finishes, the next one pops up and the pipe organ-like device plays its tune all day long. What makes emergent human consciousness so vibrant is that our pipe organs have lots of tunes to play, whereas rats, in contrast, have few. And the more we know, the richer the concert becomes. That's my story and for now I am sticking to it.
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