The Ego Tunnel: The Science of the Mind and the Myth of the Self - Thomas Metzinger (2009)
Part II. IDEAS AND DISCOVERIES
Chapter 3. OUT OF THE BODY AND INTO THE MIND
Body Image, Out-of-Body Experiences, and the Virtual Self
“Owning” your body, its sensations, and its various parts is fundamental to the feeling of being someone. Your body image is surprisingly flexible. Expert skiers, for example, can extend their consciously experienced body image to the tips of their skis. Race-car drivers can expand it to include the boundaries of the car; they do not have to judge visually whether they can squeeze through a narrow opening or avoid an obstacle—they simply feel it. Have you ever tried to walk with your eyes closed, or in the dark, tapping ahead with a stick as a blind person does? If so, you’ve probably noticed that you suddenly start to feel a tactile sensation at the end of the stick. All these are examples of what philosophers call the sense of ownership, which is a specific aspect of conscious experience—a form of automatic self-attribution that integrates a certain kind of conscious content into what is experienced as one’s self.
Neuroimaging studies have given us a good first idea of what happens in the brain when the sense of ownership, as illustrated by the rubber-hand experiment discussed in the Introduction, is transferred from a subject’s real arm to the rubber hand: Figure 2 shows areas of increased activity in the premotor cortex. It is plausible to assume that at the moment you consciously experience the rubber hand as part of your body, a fusion of the tactile and visual receptive fields takes place and is reflected by the activation of neurons in the premotor cortex.1
Figure 2: The rubber-hand illusion. The illustration on the right shows the subject’s illusion as the felt strokes are aligned with the seen strokes of the probe. The dark areas show heightened activity in the brain; the phenomenally experienced, illusory position of the arm is indicated by the light outline. The underlying activation of neurons in the premotor cortex is demonstrated by experimental data. (Botvinick & Cohen, “Rubber Hand ‘Feels’ Touch,” ibid.)
The rubber-hand illusion helps us understand the interplay among vision, touch, and proprioception, the sense of body posture and balance originating in your vestibular system. Your bodily self-model is created by a process of multisensory integration, based on a simple statistical correlation your brain has discovered. The phenomenal incorporation of the rubber hand into your self-model results from correlated tactile and visual inputs. As the brain detects the synchronicity underlying this correlation, it automatically forms a new, coherent representation. The consciously experienced sense of ownership follows.
In Matthew Botvinick and Jonathan Cohen’s study, subjects were asked to close their eyes and point to their concealed left hand; they tended to point in the direction of the rubber one, with the degree of mispointing dependent on the reported duration of the illusion. In a similar experiment, conducted by K. C. Armel and V. S. Ramachandran at UCSD’s Brain and Perception Laboratory, if one of the rubber fingers was bent backward into a physiologically impossible position, subjects not only experienced their phenomenal finger as being bent but also exhibited a significant skin-conductance reaction, indicating that unconscious autonomous mechanisms, which cannot be controlled at will, were also reacting to the assumption that the rubber hand was part of the self. Only two out of one hundred and twenty subjects reported feeling actual pain, but many pulled back their real hands and widened their eyes in alarm or laughed nervously.2
The beauty of the rubber-hand illusion is that you can try it at home. It clearly shows that the consciously experienced sense of ownership is directly determined by representational processes in the brain. Note how, in your subjective experience, the transition from shoulder to rubber hand is seamless. Subjectively, they are both part of one and the same bodily self; the quality of “ownership” is continuous and distributed evenly between them. You don’t need to do anything to achieve this effect. It seems to be the result of complex, dynamic self-organization in the brain. The emergence of the bodily self-model—the conscious image of the body as a whole—is based on a subpersonal, automatic process of binding different features together—of achieving coherence. This coherent structure is what you experience as your own body and your own limbs.
There are a number of intriguing further facts—such as the finding that subjects will mislocate their real hand only when the rubber one is in a physiologically realistic position. This indicates that “top-down” processes, such as expectations about body shape, play an important role. For example, a principle of “body constancy” seems to be at work, keeping the number of arms at two. The rubber hand displaces the real hand rather than merely being mistaken for it. Recently, psychometric studies have shown that the feeling of having a body is made up of various subcomponents—the three most important being ownership, agency, and location—which can be dissociated.3 “Me-ness” cannot be reduced to “here-ness,” and, more important, agency (that is, the performance of an action) and ownership are distinct, identifiable, and separable aspects of subjective experience. Gut feelings (“interoceptive body perception”) and background emotions are another important cluster anchoring the conscious self,4 but it is becoming obvious that ownership is closest to the core of our target property of selfhood. Nevertheless, the experience of being an embodied self is a holistic construct, characterized by part-whole relationships and stemming from many different sources.5
Phenomenal ownership is not only at the heart of conscious self-experience; it also has unconscious precursors. Classical neurology hypothesized about a body schema, an unconscious but constantly updated brain map of limb positions, body shape, and posture.6 Recent research shows that Japanese macaques can be trained to use tools even though they only rarely exhibit tool use in their natural environment.7 During successful tool use, changes occur in specific neural networks in their brains, a finding suggesting that the tools are temporarily integrated into their body schemata. When a food pellet is dispensed beyond their reach and they use a rake to bring it closer, a change is observed in their bodily self-model in the brain. In fact, it looks as though their model of their hand and of the space around it is extended to the tip of the tool; that is, on the level of the monkey’s model of reality, properties of the hand are transferred to the tool’s tip. Certain visual receptive fields now extend from a region just beyond the fingertips to the tip of the rake the monkey is holding, because the parietal lobe in its brain has temporarily incorporated the rake into the body model. In human beings, repeated practice can turn the tip of a tool into a part of the hand, and the tool can be used as sensitively and as skillfully as the fingers.
Recent neuroscientific data indicate that any successful extension of behavioral space is mirrored in the neural substrate of the body image in the brain. The brain constructs an internalized image of the tool by assimilating it into the existing body image. Of course, we do not know whether monkeys actually have the conscious experience of ownership or only the unconscious mechanism. But we do know of several similarities between macaques and human beings that make plausible the assumption that the macaques’ morphed and augmented bodily self is conscious.
One exciting aspect of these new data is that they shed light on the evolution of tool use. A necessary precondition of expanding your space of action and your capabilities by using tools clearly seems to be the ability to integrate them into a preexisting self-model. You can engage in goal-directed and intelligent tool use only if your brain temporarily represents the tools as part of your self. Intelligent tool use was a major achievement in human evolution. One can plausibly assume that some of the elementary building blocks of human tool-use abilities existed in the brains of our ancestors, 25 million years ago. Then, due to some not-yet-understood evolutionary pressure, they exploded into what we see in humans today.8 The flexibility in the monkey’s body schema strongly relies on properties of body maps in its parietal lobe. The decisive step in human evolution might well have been making a larger part of the body model globally available—that is, accessible to conscious experience. As soon as you can consciously experience a tool as integrated into your bodily self, you can also attend to this process, optimize it, form concepts about it, and control it in a more fine-grained manner—performing what today we call acts of will. Conscious self-experience clearly is a graded phenomenon; it increases in strength as an organism becomes more and more sensitive to an internal context and expands its capacities for self-control.
Figure 3: Integrating touch and sight. The subject tries to move a coin (small dark circle) onto a tray with her own hand and with the help of a tool. In the figure on the right, the integrated experience of vision and touch is transferred from the hand to the tip of a tool. The dotted lines trace the subject’s gaze direction; the arrows indicate the direction of the movement. The large white circle shows the area where—according to the conscious model of reality—the sense of sight and the sense of touch are integrated. Figure courtesy of Angelo Maravita.
Monkeys also seem able to incorporate into their bodily self-model a visual image of their hand as displayed on a computer monitor. If an image of a snake or a spider approaches the image of the hand on the screen, the animal retracts its real hand. Monkeys can even learn to control a brain-machine interface that lets them grasp objects with a robot arm controlled by certain parts of their brain.9 Perhaps most exciting from a philosophical perspective is the idea that all of this may have contributed to the evolutionary emergence of a quasi-Cartesian “meta-self,” the capacity to distance yourself from your bodily self—namely, by beginning to see your own body as a tool.10
Figure 4: Japanese macaques exhibit intelligent tool use. They can use a rake to reach a food pellet (bottom), and they can monitor their own movements with the help of images on a computer screen, even when their hands are invisible (middle and top): A mere extension of behavioral space, or an extension of the phenomenal self-model? Figures courtesy of Atsushi Iriki.
Clearly, the visual image of the robot arm, just as in the rubber-hand illusion, is embedded in the dancing self-pattern in the macaque’s brain. The integration of feedback from the robot arm into this self-model is what allows the macaque to control the arm—to incorporate it functionally into a behavioral repertoire. In order to develop intelligent tool use, the macaque first had to embed this rake in its self-model; otherwise, it could not have understood that it could use the rake as an extension of its body. There is a link between selfhood and extending global control.
Human beings, too, treat virtual equivalents of their body parts as seen on a video screen as extensions of their own bodies. Just think of mouse pointers on computer desktops or controllable fantasy figures in video games. This may explain the sense of “presence” we sometimes have when playing these ultrarealistic games. Incorporation of artificial actuators into widely distributed brain regions may someday allow human patients successfully to operate advanced prostheses (which, for example, send information from touch and position sensors to a brain-implanted, multichannel recording device via a wireless link), while also enjoying a robust conscious sense of ownership of such devices. All of this gives us a deeper understanding of ownership. On higher levels, ownership is not simply passive integration into a conscious self-model: More often it has to do with functionally integrating something into a feedback loop and then making it part of a control hierarchy. It now looks as if even the evolution of language, culture, and abstract thought might have been a process of “exaptation,” of using our body maps for new challenges and purposes—a point to which I return in the chapter on empathy and mirror neurons. Put simply, exaptation is a shift of function for a certain trait in the process of evolution: Bird feathers are a classic example, because initially these evolved “for” temperature regulation but later were adapted for flight. Here, the idea is that having an integrated bodily self-model was an extremely useful new trait because it made a host of unexpected exaptations possible.
Clearly, a single general mechanism underlies the rubber-hand illusion, the evolution of effortless tool use, the ability to experience bodily presence in a virtual environment, and the ability to control artificial devices with one’s brain. This mechanism is the self-model, an integrated representation of the organism as a whole in the brain. This representation is an ongoing process: It is flexible, can be constantly updated, and allows you to own parts of the world by integrating them into it. Its content is the content of the Ego.
THE OUT-OF-BODY EXPERIENCE
My own interest in consciousness arose from a variety of sources, which were mostly academic but also autobiographical. At some points, the theoretical problem appeared directly and unexpectedly in my life. As a young man, I encountered a series of disturbing experiences, of which the following is a typical instance:
It is spring, 1977. I am nineteen years old. I am lying in bed, on my back, going to sleep, deeply relaxed yet still alert. The door is half open, and light seeps in. I hear my family’s voices from the hallway and the bathroom and pop music from my sister’s bedroom. Suddenly I feel as though my bed is sliding into a vertical position, with the head of the bed moving toward the ceiling. I seem to leave my physical body, rising slowly into an upright position. I can still hear the voices, the sound of people brushing their teeth, and the music, but my sight is somewhat blurred. I feel a mixture of amazement and rising panic, sensations that eventually lead to something like a faint, and I find myself back in bed, once again locked into my physical body.
This brief episode was startling for its clarity, its crisp and lucid quality, and the fact that from my point of view it appeared absolutely real. Six years later, I was aware of the concept of the out-of-body experience (OBE), and when such episodes occurred, I could control at least parts of the experience and attempt to make some verifiable observations. As I briefly pointed out in the Introduction, OBEs are a well-known class of states in which one undergoes the highly realistic illusion of leaving one’s physical body, usually in the form of an etheric double, and moving outside of it. Most OBEs occur spontaneously, during sleep onset or surgical operations or following severe accidents. The classic defining characteristics include a visual representation of one’s body from a perceptually impossible, third-person perspective (for example, lying on the bed below) plus a second representation of one’s body, typically hovering above.
Figure 5: Kinematics of the phenomenal body image during OBE onset: The “classical” motion pattern according to S. Muldoon and H. Carrington, The Projection of the Astral Body (London: Rider & Co., 1929).
At about the same time, in the early 1980s, I underwent an equally disturbing experience in my intellectual life. I was writing my philosophy dissertation at Johann-Wolfgang-Goethe University on the discussion of the so-called mind-body problem that ensued after Gilbert Ryle’s 1949 book, The Concept of Mind. In this period, various philosophers, from Ullin T. Place to Jaegwon Kim, had developed nearly a dozen major theoretical proposals to solve that age-old puzzle, and great progress had been made. I had grown up in a more traditionally oriented philosophy department, which was dominated by the political philosophy of the Frankfurt School. There, almost no one seemed aware of the enormous progress in analytical philosophy of mind. To my great surprise, I discovered that in the really convincing, substantial work at the research frontier, materialism had long ago become the orthodoxy. Almost no one seemed even remotely to consider the possibility of the existence of a soul. There were very few dualists—except on the Continent. It was sobering to realize that some forty years after the end of World War II, with practically all of the German-Jewish intelligentsia and other intellectuals either murdered or driven into exile, many lines of tradition and teacher-student relationships were severed, and German philosophy had been largely decoupled from the global context of discussion. Most German philosophers would not read what was being published in English. Suddenly some of the philosophical debates I witnessed in German universities increasingly struck me as badly informed, a bit provincial, and lacking awareness of where humankind’s great project of constructing a comprehensive theory of mind actually stood. I gradually became convinced, by my own reading, that indeed there was no convincing empirical evidence of conscious experience possibly taking place outside the brain, and that the general trend at the frontier of the very best of philosophy of mind clearly pointed in the opposite direction. On the other hand, I had myself repeatedly experienced leaving my body—vividly and in a crystal-clear way. What to do?
There was only one answer: I had to turn these episodes into a controllable and repeatable state of consciousness, and I had to settle experimentally the issue of whether it was possible to make verifiable observations in the out-of-body state. I read everything on OBEs I could find, and I tried various psychological techniques to produce the phenomenon deliberately. In a series of pitiless self-experiments, I stopped drinking liquids at noon, stared at a glass of water by the kitchen sink with the firm intention of returning to it in the out-of-body state, and went to bed thirsty with half a tablespoon of salt in my cheek (you can try this at home). In the scientific literature, I had read that OBEs were associated with the anesthetic ketamine. So when I had to undergo minor surgery in 1985, I talked the anesthetist into changing the medication so that I could experience the wake-up phase of ketamine-induced anesthesia in a medically controlled, experimental setting. (Do not try this at home!) Both types of research projects failed, and I gave up on them many years ago. I was never able to go beyond pure first-person phenomenology—that is, to make a single verifiable observation in the OBE state that could even remotely count as evidence for the genuine separability of consciousness and the brain.
In some of my recent research, I have been trying to disentangle the various layers of the conscious self-model—of the Ego. I firmly believe that, from a theoretical perspective, it is most important first to isolate clearly the simplest form of self-consciousness. What is the most fundamental, the earliest sense of selfhood? Can we subtract thinking, feeling, and autobiographical memory and still have an Ego? Can we remain in the Now, perhaps even without any acts of will and in the absence of any bodily behavior, and still enjoy phenomenal selfhood? Philosophers in the past have made the mistake of almost exclusively discussing high-level phenomena such as mastery of the first-person pronoun “I” or cognitively mediated forms of intersubjectivity. I contend that we must pay attention to the causally enabling and necessary low-level details first, to what I call “minimal phenomenal selfhood”;11 we must ground the self, and we must do it in an interdisciplinary manner. As you will see, OBEs are a perfect entry point.
Not too long ago, OBEs were something of a taboo zone for serious researchers, just as consciousness was in the early 1980s; both have been considered career-limiting moves by junior researchers. But after decades of neglect, OBEs have now become one of the hottest topics in research on embodiment and the conscious self. Olaf Blanke, whom we met in the Introduction, and I are studying the experience of disembodiment in order to understand what an embodied self truly is.
From a philosophical perspective, OBEs are interesting for a number of reasons. The phenomenology of OBEs inevitably leads to dualism and to the idea of an invisible, weightless, but spatially extended second body. I believe this may actually be the folk-phenomenological ancestor of the notion of a “soul” and of the philosophical protoconcept of the mind.12 The soul is the OBE-PSM. The traditional concept of an immortal soul that exists independently of the physical body probably has a recent neurophenomenological correlate. In its origins, the “soul” may have been not a metaphysical notion but simply a phenomenological one: the content of the phenomenal Ego activated by the human brain during out-of-body experiences.
In the history of ideas, contemporary philosophical and scientific debates about the mind developed from this protoconcept—an animist, quasi-sensory theory about what it means to have a mind. Having a mind meant having a soul, an ethereal second body. This mythical idea of a “subtle body” that is independent of the physical body and is the carrier of higher mental functions, such as attention and cognition, is found in many different cultures and at many times—for instance, in prescientific theories about a “breath of life.”13 Examples are the Hebrew ruach, the Arabic ruh, the Latin spiritus, the Greek pneuma, and the Indian prana. The subtle body is a spatially extended entity that was said to keep the physical body alive and leave it after death.14 It is also known in theosophy and in other spiritual traditions; for instance, as “the resurrection body” and “the glorified body” in Christianity, “the most sacred body” and “supracelestial body” in Sufism, “the diamond body” in Taoism and Vajrayana, “the light body” or “rainbow body” in Tibetan Buddhism.
My theory—the self-model theory of subjectivity—says that this subtle body does indeed exist, but it is not made of “angel stuff ” or “astral matter.” It is made of pure information, flowing in the brain.15 Of course, the “flow of information” is just another metaphor, but the information-processing level of description is the best we have at this stage of research. It creates empirically testable hypotheses, and it allows us to see things we could not see before. The subtle body is the brain’s self-model, and scientific research on the OBE shows this in a particularly striking way.
First-person reports of OBEs are available in abundance, and they, too, come from all times and many different cultures. I propose that the functional core of this kind of conscious experience is formed by a culturally invariant neuropsychological potential common to all human beings. Under certain conditions, the brains of all human beings can generate OBEs. We are now beginning to understand the properties of the functional and representational architecture involved. Examining the phenomenology in OBE reports will help us to understand not only these properties as such but also their neural implementation. There may well be a spatially distributed but functionally distinct neural correlate for the OBE state. In her work, the psychologist Susan J. Blackmore has propounded a reductionist theory of out-of-body experiences, describing them as models of reality created by brains that are cut off from sensory input during stressful situations and have to fall back on internal sources of information .16 She drew attention to the remarkable fact that visual cognitive maps reconstructed from memory are most often organized from a bird’s-eye perspective. Close your eyes and remember the last time you were walking along the beach. Is your visual memory one of looking out at the scene itself? Or is it of observing yourself, perhaps from somewhere above, walking along the coastline? For most people, the latter is the case.
When I first met Blackmore, in Tübingen in 1985, and told her about several out-of-body experiences of my own, she kept asking me to describe, painstakingly, how I moved during these episodes. Not until then did I realize that when I moved around my bedroom at night in the OBE state, it was not in a smooth, continuous path, as in real-life walking or as one might fly in a dream. Instead, I moved in “jumps”—say, from one window to the next. Blackmore has hypothesized that during OBEs we move in discrete shifts, from one salient point in our cognitive map to the next. The shifts take place in an internal model of our environment—a coarse-grained internal simulation of landmarks in settings with which we are familiar. Her general idea is that the OBE is a conscious simulation of the world—spatially organized from a third-person perspective and including a realistic representation of one’s own body—and it is highly realistic because we do not recognize it as a simulation.17
Blackmore’s theory is interesting because it treats OBEs as behavioral spaces. And why shouldn’t they be internally simulated behavioral spaces? After all, conscious experience itself seems to be just that: an inner representation of a space in which perceptions are meaningfully integrated with one’s behavior. What I found most convincing about Blackmore’s OBE model were the jumps from landmark to landmark, a phenomenological feature I had overlooked in my own OBE episodes.
My fifth OBE was particularly memorable. It took place at about 1:00 A.M., on October 31, 1983:
My vision was generally poor during OBE experiences, as would be expected in a dark bedroom at night. When I realized I was unable to flip the light switch in front of which I found myself standing in my OBE state, I became extremely nervous. In order not to ruin everything and lose a precious opportunity for experiments, I decided to stay put until I had calmed down. Then I attempted to walk to the open window, but instead found myself smoothly gliding there, arriving almost instantaneously. I carefully touched the wooden frame, running my hands over it. Tactile sensations were clear but different—that is, the sensation of relative warmth or cold was absent. I leaped through the window and went upward in a spiral. A further phenomenological feature accompanied this experience—the compulsive urge to visualize the headline in the local newspapers: “WAS IT ATTEMPTED SUICIDE OR AN EXTREME CASE OF SOMNAMBULISM? PHILOSOPHY STUDENT DROPS TO HIS DEATH AFTER SLEEPWALKING OUT THE WINDOW.” A bit later, I was lying on top of my physical body in bed again, from which I rose in a controlled fashion, for the second time now. I tried to fly to a friend’s house in Frankfurt, eighty-five kilometers away, where I intended to try to make some verifiable observations. Just by concentrating on my destination, I was torn forward at great speed, through the wall of my bedroom, and immediately lost consciousness. As I came to, half-locked into my physical body, I felt my clarity decreasing and decided to exit my body one last time.
These incidents, taken from what was a more comprehensive experience, demonstrate a frequently overlooked characteristic of self-motion in the OBE state—namely, that the body model does not move as the physical body would, but that often merely thinking about a target location gets you there on a continuous trajectory. Vestibulo-motor sensations are strong in the OBE state (indeed, one fruitful way of looking at OBEs is as complex vestibulo-motor hallucinations), but weight sensations are only weakly felt, and flying seems to come naturally as the logical means of OBE locomotion. Because most OBEs happen at night, another implicit assumption is that you cannot see very well. That is, if you are jumping from one landmark in your mental model of reality to the next, it is not surprising that the space between two such salient points is experientially vague or underdetermined; at least I simply didn’t expect to see much detail. Note that the absence of thermal sensations and the short blackouts between different scenes are also well documented in dream research (see chapter 5).
Here are some other first-person accounts of OBEs. This one comes from Swiss biochemist Ernst Waelti, who conducts research at the University of Bern’s Institute of Pathology on virosomes for drug delivery and gene transfer:
I awoke at night—it must have been about 3 A.M.—and realized I was unable to move. I was absolutely certain I was not dreaming, as I was enjoying full consciousness. Filled with fear about my current condition, I had only one goal—namely, to be able to move my body again. I concentrated all my will power and tried to roll over onto my side: Something rolled, but not my body—something that was me, my whole consciousness, including all of its sensations. I rolled onto the floor beside the bed. While this was happening, I did not feel bodiless but as if my body consisted of a substance constituted of a mixture of gas and liquid. To this day, I have not forgotten the amazement that gripped me when I felt myself falling to the floor, but the expected hard impact never came. Had my normal body fallen like that, my head would have collided with the edge of my bedside table. Lying on the floor, I was seized by panic. I knew I possessed a body, and I had only one overwhelming desire: to be able to control it again. With a sudden jolt, I regained control of it, without knowing how I managed to get back into it.
Again from Waelti, about another occasion:
In a dazed state, I went to bed at 11 P.M. and tried to fall asleep. I was restless and turned over frequently, causing my wife to grumble briefly. Now I forced myself to lie in bed motionless. For a while, I dozed, then felt the need to move my hands, which were lying on the blanket, into a more comfortable position. In the same instant, I realized that … my body was lying there in some kind of paralysis. Simultaneously, I found I could pull my hands out of my physical hands, as if the latter were just a stiff pair of gloves. The process of detachment started at the fingertips, in a way that could be felt clearly, with a perceptible sound, a kind of crackling. This was precisely the movement I had intended to carry out with my physical hands. With this, I detached from my body and floated out of it head first, attaining an upright position, as if I were almost weightless. Nevertheless, I had a body, consisting of real limbs. You have certainly seen how elegantly a jellyfish moves through the water. I could now move around with the same ease.
I lay down horizontally in the air and floated across the bed, like a swimmer who has pushed himself off the edge of a swimming pool. A delightful feeling of liberation arose within me. But soon I was seized by the ancient fear common to all living creatures—the fear of losing my physical body. It sufficed to drive me back into my body.18
Figure 6 a & b: How the conscious image of the body moves during OBE onset. Two alternative but equally characteristic motion patterns as described by Swiss biochemist Ernst Waelti (1983).
As noted, the sleep paralysis Waelti describes is not a necessary condition for OBEs. They frequently occur following accidents, in combat situations, or during extreme sports—for instance in high-altitude climbers or marathon runners:
A Scottish woman wrote that, when she was 32 years old, she had an OBE while training for a marathon. “After running approximately 12-13 miles … I started to feel as if I wasn’t looking through my eyes but from somewhere else… . I felt as if something was leaving my body, and although I was still running along looking at the scenery, I was looking at myself running as well. My ‘soul’ or whatever, was floating somewhere above my body high enough up to see the tops of the trees and the small hills.”19
Various studies show that between 8 and 15 percent of people in the general population have had at least one OBE.20 There are much higher incidences in certain groups of people, such as students (25 percent), paranormal believers (49 percent), and schizophrenics (42 percent); there are also OBEs of neurological origin, as in epileptics.21
A 29-year-old woman has had absence seizures since the age of 12 years. The seizures occur five times a week without warning. They consist of a blank stare and brief interruption of ongoing behavior, sometimes with blinking. She had an autoscopic experience at age 19 years during the only generalized tonoclonic seizure she has ever had. While working in a department store she suddenly fell, and she said, “The next thing I knew I was floating just below the ceiling. I could see myself lying there. I wasn’t scared; it was too interesting. I saw myself jerking and overheard my boss telling someone to ‘punch the timecard out’ and that she was going with me to the hospital. Next thing, I was in space and could see Earth. I felt a hand on my left shoulder, and when I went to turn around, I couldn’t. Then I looked down and I had no legs; I just saw stars. I stayed there for a while until some inner voice told me to go back to the body. I didn’t want to go because it was gorgeous up there, it was warm—not like heat, but security. Next thing, I woke up in the emergency room.” No abnormalities were found on the neurological examination. Skull CT scan was normal. The EEG demonstrated generalized bursts of 3/s spike-and-wave discharges.22
At first, the realistic quality of these OBEs seems to argue against their hallucinatory nature. More interesting, though, is how veridical elements and hallucination are integrated into a single whole. Often, the appearance/reality distinction is available: There is insight, but this insight is only partial. One epileptic patient noted that his body, perceived from an external perspective, was dressed in the clothes he was really wearing, but, curiously, his hair was combed, though he knew it had been uncombed before the onset of the episode. Some epileptic patients report that their hovering body casts a shadow; others do not report seeing the shadow. For some, the double is slightly smaller than life-size. We can also see the insight component in the first report by Ernst Waelti previously quoted: “Had my normal body fallen like that, my head would have collided with the edge of my bedside table.”
Another reason the OBE is interesting from a philosophical perspective is that it is the best known state of consciousness in which two self-models are active at the same time. To be sure, only one of them is the “locus of identity,” the place where the agent (in philosophy, an entity that acts) resides. The other self-model—that of the physical body lying, say, on the bed below—is not, strictly speaking, a self-model, because it does not function as the origin of the first-person perspective. This second self-model is not a subject model. It is not the place from which you direct your attention. On the other hand, it is still your own body that you are looking at. You recognize it as your own, but now it is not the body as subject, as the locus of knowledge, agency, and conscious experience. That is exactly what the Ego is. These observations are interesting because they allow us to distinguish different functional layers in the conscious human self.
Interestingly, there is a range of phenomena of autoscopy (that is, the experience of viewing your body from a distance) that are probably functionally related to OBEs, and they are of great conceptual interest. The four main types are autoscopic hallucination, heautoscopy, out-of-body experience, and the “feeling of a presence.” In autoscopic hallucinations and heautoscopy, patients see their own body outside, but they do not identify with it and don’t have the feeling that they are “in” this illusory body. However, in heautoscopy, things may sometimes go back and forth, and the patient doesn’t know which body he is in right now. The shift in the visuospatial first-person perspective, localization, and identification of the self with an illusory body at an extracorporeal position are complete in out-of-body experiences. Here the self and the visuospatial first-person perspective are localized outside one’s body, and people see their physical body from this disembodied location. The “feeling of a presence”—which has also been caused by directly stimulating the brain with an electrode—is particularly interesting: It is not a visual own-body illusion but an illusion during which a second illusory body is only felt (but not seen).23
Figure 7: Disturbances of the self and underlying brain areas. All these phenomena show that not only identification with and localization of body parts but also the conscious representation of the entire body and the associated sense of selfhood can be disturbed. All four types of experience are caused by multisensory disintegration having a clear-cut neurological basis (see light areas); brain tumors and epilepsy are among the most frequent causes for heautoscopy. Modified from O. Blanke; Illusions visuelles. In A.B. Safran, A. Vighetto, T. Landis, E. Cabanis (eds.), Neurophtalmologie (Paris: Madden, 2004), 147-150.
What about personality correlates? Differential psychology has shown that significant personality traits of people who frequently experience OBEs include openness to new experience, neuroticism, a tendency toward depersonalization (an emotional disorder in which there is loss of contact with one’s own personal reality, accompanied by feelings of unreality and strangeness; often people feel that their body is unreal, changing, or dissolving), schizotypy (sufferers experience distorted thinking, behave strangely, typically have few, if any, close friends, and feel nervous around strangers), borderline personality disorder, and histrionics.24 Another recent study links OBEs to a capacity for strong absorption—that is, experiencing the phenomenal world, in all its aspects and with all one’s senses, in a manner that totally engages one’s attention and interest—and somatoform dissociation (in part, a tendency to cut one’s attention off from bodily and motion stimuli), and points out that such experiences should not automatically be construed as pathological.25
It is also interesting to take a closer look at the phenomenology of OBEs. For example, the “head exit” depicted in figure 6a is found in only 12.5 percent of cases. The act of leaving your body is abrupt in 46.9 percent of cases but can also vary from slow (21.9 percent) to gradual and very slow (15.6 percent).26 Many OBEs are short, and one recent study found a duration of less than five minutes in nearly 40 percent of cases and less than half a minute in almost 10 percent. In a little more than half the cases, the subjects “see” their body from an external perspective, and 62 percent do so from a short distance only.27 Many OBEs involve only a passive sense of floating in a body image, though the sense of selfhood is robust. In a recent study more than half the subjects reported being unable to control their movements, whereas nearly a third could. Others experienced no motion at all.28 Depending on the study, 31 to 84 percent of subjects find themselves located in a second body (but this may also be an indefinite spatial volume), and about 31 percent of OBEs are actually “asomatic”—they are experienced as bodiless and include an externalized visuospatial perspective only. Vision is the dominant sensory modality in 68.8 percent, hearing in 15.5 percent. An older study found the content of the visual scene to be realistic (i.e., not supernatural) in more than 80 percent of cases.29
I have always believed that OBEs are important for any solid, empirically grounded theory of self-consciousness. But I had given up on them long ago; there was just too little substantial research, not enough progress over decades, and most of the books on OBEs merely seemed to push metaphysical agendas and ideologies. This changed in 2002, when Olaf Blanke and his colleagues, while doing clinical work at the Laboratory of Presurgical Epilepsy Evaluation of the University Hospital of Geneva, repeatedly induced OBEs and similar experiences by electrically stimulating the brain of a patient with drug-resistant epilepsy, a forty-three-year-old woman who had been suffering from seizures for eleven years. Because it was not possible to find any lesions using neuroimaging methods, invasive monitoring had to be undertaken to locate the seizure focus precisely. During the stimulation of the brain’s right angular gyrus, the patient suddenly reported something strongly resembling an OBE. The epileptic focus was located more than 5 cm from the stimulation site in the medial temporal lobe. Electrical stimulation of this site did not induce OBEs, and OBEs were also not part of the patient’s habitual seizures.
Initial stimulations induced feelings that the patient described as “sinking into the bed” or “falling from a height.” Increasing the current amplitude to 3.5 milliamperes led her to report, “I see myself lying in bed, from above, but I see only my legs and lower trunk.” Further stimulations also induced an instantaneous feeling of “lightness” and of “floating” about six feet above the bed. Often she felt as though she were just below the ceiling and legless.
Meanwhile, not only OBEs but also the “feeling of a presence” have been caused by direct electrical brain stimulation (see figure 9).
Blanke’s first tentative hypothesis was that out-of-body experiences, at least in these cases, resulted from a failure to integrate complex somatosensory and vestibular information.30 In more recent studies, he and his colleagues localized the relevant brain lesion or dysfunction at the temporo-parietal junction (TPJ).31 They argue that two separate pathological conditions may have to come together to cause an OBE. The first is disintegration on the level of the self-model, brought about by a failure to bind proprioceptive, tactile, and visual information about one’s body. The second is conflict between external, visual space and the internal frame of reference created by vestibular information, i.e., our sense of balance. We all move within an internal frame of reference created by our vestibular organs. In vertigo or dizziness, for example, we have problems with vestibular information while experiencing the dominant external, visual space. If the spatial frame of reference created by our sense of balance and the one created by vision come apart, the result could well be the conscious experience of seeing one’s body in a position that does not coincide with its felt position.
Figure 9: A recent study conducted by Dr. Olaf Blanke provides new scientific insight into experiences more often left to paranormal explanations. Stimulating a part of the brain called the angular gyrus on opposing sides yielded two distinct results: the feeling of a bodily presence behind oneself and an OBE. (Source: Dr. Olaf Blanke. Figure from Graham Roberts/The New York Times.)
Figure 8 shows the electrode site on the right angular gyrus, where electrical stimulation repeatedly induced not only OBEs but also the feeling of transformed arms and legs or whole-body displacements. Reprinted by permission from Macmillan Publishers Ltd: Nature, Volume 419, 19, September 2002.
It is now conceivable that some OBEs could be caused by a cerebral dysfunction at the TPJ. In epileptic patients who report experiencing OBEs, a significant activation at the TPJ can be observed when electrodes are implanted in the left hemisphere.32 Interestingly, when healthy subjects are asked to imagine their bodies being in a certain position, as if they were seeing themselves from a characteristic perspective of the OBE, the same brain region is activated in less than half a second. If this brain region is inhibited by a procedure called transcranial magnetic stimulation, this transformation of the mental model of one’s body is impaired. Finally, when an epileptic patient whose OBEs were caused by damage to the temporo-parietal junction was asked to simulate mentally an OBE self-model, this led to a partial activation of the seizure focus. Taken together, these observations point to an anatomical link among three different but highly similar types of conscious experiences: real, seizure-caused OBEs; intended mental simulations of OBEs in healthy subjects; and intended mental simulations of OBEs in epileptic patients.
Recent findings show that the phenomenal experience of disembodiment depends not just on the right half of the temporo-parietal junction but also on an area in the left half, called the extrastriate body-area. A number of different brain regions may actually contribute to the experience. Indeed, the OBE may turn out not to be one single and unified target phenomenon. For example, the phenomenology of exiting the body varies greatly across different types of reports: The initial seconds clearly seem to differ between spontaneous OBEs in healthy subjects and those experienced by the clinical population, such as epileptic patients. The onset may also be different in followers of certain spiritual practices. Moreover, there could be a considerable neurophenomenological overlap between lucid dreams (see chapter 5) and OBEs as well as body illusions in general.
Figure 10: Brain areas that are active in mental transformations of one’s body, predominantly at the right temporo-parietal junction. (Figure courtesy of Olaf Blanke, from Blanke et al., “Linking Out-of-Body Experience and Self-Processingto Mental Own-Body Imagery and the Temporoparietal Junction,” Jour. Neurosci. 25:550-557, 2005.)
VIRTUAL OUT-OF-BODY EXPERIENCES
In 2005, Olaf, his PhD student Bigna Lenggenhager, and I embarked on a series of virtual-reality experiments. Our first goal was to turn the OBE into a fully replicable phenomenon in healthy subjects. Proper research required that we be able to investigate and repeat out-of-body experiences in the lab. The guiding question was whether there could be an integrated kind of bodily self-consciousness that is a phenomenal confabulation. In short, could one experience a hallucinated and a bodily self at the same time, a full-body analog of the rubber-hand illusion?
Here is an example of one of our early experimental protocols using the paraphernalia of virtual reality: a head-mounted display (HMD) consisting of goggles that showed two separate images to each eye, creating the three-dimensional illusion of being in a virtual room. Subjects were able to see their own backs, which were filmed from a distance of 2 meters and projected into the three-dimensional space in front of them with the help of a 3D-encoder. When I acted as the subject of the experiment, I felt as if I had been transposed into a 3D-version of René Magritte’s painting La reproduction interdite. Suddenly I saw myself from the back, standing in front of me.
Figure 11: Magritte’s La Reproduction Interdite (1937)
While I was looking at my own back as seen in the head-mounted display, Bigna Lenggenhager was stroking my back, while the camera was recording this action. As I watched my own back being stroked, I immediately had an awkward feeling: I felt subtly drawn toward my virtual body in front of me, and I tried to “slip into” it. This was as far as things went.
Figure 12: Creating a whole-body analog of the rubber-hand illusion. (A) Participant (darker trousers) sees through a HMD his own virtual body (lighter-colored trousers) in 3D, standing 2 m in front of him and being stroked synchronously or asynchronously at the participant’s back. In other conditions, the participant sees either (B) a virtual fake body (lighter trousers) or (C) a virtual noncorporeal object (light gray) being stroked synchronously or asynchronously at the back. Dark colors indicate the actual location of the physical body or object, whereas light colors represent the virtual body or object seen on the HMD. Illustration by M. Boyer.
Our studies became more systematic. All of our subjects would be shown their own backs being stroked (this was the “own-body condition”) and in a subsequent test would be shown either the back of a mannequin (the “fake-body condition”) or a large rectangular slab (which didn’t look like a body at all, the “object condition”) being stroked. An additional condition was the degree of synchronicity between the seen and the felt stroking, which could be varied by projecting the camera image into cyberspace with a certain time lag.
Afterwards, an independent measure for the strength of the illusion was introduced. They were blindfolded, moved around and disoriented, as in a game of blindman’s buff, and then asked to return to their initial position.
At the end of the experiment, the subjects were asked to fill out a questionnaire about their experiences. Results showed that for the synchronous conditions in which they were observing either their own body or a mannequin, they often felt as though the virtual figure was their own body, actually identifying with and “jumping into” it. This impression was less likely to occur in the case of the wooden slab, as well as in all of the asynchronous conditions. The synchronous experiments also showed a significantly larger shift by the subjects toward the projected real or fake body than did the asynchronous control conditions. In other control conditions, subjects observed a screen without a body in it and were then displaced (visual scene), or were simply displaced only. These data suggest that locating the “self ” in the case of conflicting visual and somatosensory input is as prone to error as was reported for a body part in the rubber-hand illusion.
Here is what I call the “embedding principle”: The bodily self is phenomenally represented as inhabiting a volume in space, whereas the seeing self is an extensionless point—namely, the center of projection for our visuospatial perspective, the geometrical origin of our perspectival visual model of reality. Normally this point of origin (behind the eyes, as if a little person were looking out of them as one looks out a window) is within the volume defined by the felt bodily self. Yet, as our experiments demonstrated, seeing and bodily self can be separated, and the fundamental sense of selfhood is found at the location of the visual body representation.
THE ESSENCE OF SELFHOOD
Why is all this information important for the philosophy of the conscious self? Can it really help us to find the conceptual essence of selfhood, to pinpoint what all self-conscious beings in the universe have in common? Is it really a step toward the big picture mentioned in the Introduction? The answer is yes: What we really want are the constitutive conditions for selfhood. We want to know what is truly necessary and what is perhaps only sufficient to bring about an Ego, the fundamental feeling of “being someone.” For example, in our quest for the core of the conscious self, it would be progress if one could differentiate between what is merely causally enabling, and what is strictly necessary under the laws of nature holding in this universe. Our experiments demonstrate that agency is not necessary, because they selectively manipulate only two dimensions: self-identification (with the content of a conscious body image) and self-localization (in a spatial frame of reference). They do so with the subject in a passive condition, without will or bodily agency. This shows how the target phenomenon—self-consciousness—can be causally controlled by multisensory conflict alone. That is important because if we combine the discovery that this can be achieved simply by creating a conflict between sight and touch with the fact that the shift in visual perspective during OBEs can also be caused by an epileptic seizure or by direct stimulation with an electrode in the brain, we get a much better idea of what the simplest form of self-consciousness might be. It must be something very local, something in the brain itself, and it is independent of motor control, of moving your body.33
We know more: A seeing self also is not necessary. You can shut the windows in front of the little man behind your eyes by closing your eyelids. The seeing self disappears; the Ego remains. You can be a robust, conscious self even if you are emotionally flat, if you do not engage in acts of will, and also in the absence of thought. Emotions, will, and thoughts are not necessary to the fundamental sense of selfhood. Every meditator (remember chapter 1) can confirm that you may settle into a calm, emotionally neutral state, deeply relaxed and widely alert, a state of pure observation, without any thought, while a certain elementary form of bodily self-consciousness remains. Let us call this “selfhood-as-embodiment.”
So what is the essence? Location in space and time plus a transparent body image seem to be very close. The rubber-hand illusion manipulates only the experience of ownership of body parts. The full-body illusion manipulates ownership of the body as a whole. Could this finally be the simplest form of selfhood, something we could metaphorically describe as the fundamental experience of “global ownership”? This, I believe, is a misleading idea. Global ownership is a dangerous concept, because it introduces two distinct entities plus a relation, the body and an invisible self, someone who possesses the body. It is the body that possesses itself: Owning something means to be able to control it, and selfhood is intimately related to the very moment in which the body discovers that it can control itself—as a whole. It is exactly what happens when you wake up in the morning, when you “come to yourself.”
Here is an interim theory: Minimal self-consciousness is not control, but what makes control possible. It includes an image of the body in time and space (location) plus the fact that the organism creating this image does not recognize it as an image (identification). So we must have a Now, plus a spatial frame of reference, and a transparent body-model. Then we need a visual (or auditory) perspective originating within the body volume, a center of projection embedded in the volume of the body. But the really interesting step is the one from the minimal self to a slightly more robust first-person perspective. It is the step from selfhood-as-embodiment to selfhood-as-subjectivity.
The decisive transition takes place when the system is already given to itself through minimal self-consciousness and then, in addition, represents itself as being directed toward an object. I believe this happens exactly when we first discover that we can control the focus of attention. We understand that we can draw things from the fringe of consciousness into the center of experience, holding them in the spotlight of attention or deliberately ignoring them—that we can actively control what information appears in our mind. Now we have a perspective, because we have an inner image of ourselves as actually representing, as subjects directed at the world. Now we can, for the first time, also attend to our own body as a whole—we become self-directed. Inwardness appears. The essence of this slightly stronger form of selfhood—what a philosopher might call its “representational content”—is attentional agency plus the realization that the body is now available for global control. It is inner knowledge, not of ongoing motor behavior or of perceptual and attentional processing directed at the world or single body parts, but of the body as a single multisensory whole, which now becomes functionally available for global control. Conscious selfhood is a deep-seated form of knowledge about oneself, providing information about new causal properties. This inner knowledge has nothing to do with language or concepts. An animal could have it.
What exactly is this “coming to”? Here is another lesson to be learned from the careful study of OBEs: Some OBErs act, but others have a passive experience of floating in a body image; often the second body is not even available for conscious control, yet the sense of selfhood is robust. In a recent study, 53.1 percent of subjects reported not being able to control their own movements (whereas 28.1 percent did, and others didn’t experience motion at all).34 So it clearly is the more subtle experience of controlling the focus of attention, which seems to be at the heart of inwardness—selfhood-as-subjectivity is intimately related to “modeling mental resource allocation” as some sober computational neuroscientist might say. The correct philosophical term would be “epistemic control”: The mental action of expanding your knowledge about the world, for example, by selecting what you will know, while at the same time excluding what you will, for now, ignore. What this adds is a strong first-person perspective, the experience of being directed at an object. Subjective awareness in this sense of having a perspective by being directed at the world is body image (in space and time) plus the experience of attentional control; inwardness appears when we attend to the body itself. Recall how, in chapter 2, I said that consciousness is the space of attentional agency. Selfhood as inwardness emerges when an organism for the first time actively attends to its body as a whole. If a global model of the body is integrated into the space of attentional agency, a richer phenomenal self emerges. It is not necessary to think, it is not necessary to move; the availability of the body as a whole for focal attention is enough to create the most fundamental sense of selfhood-as-inwardness—that is, the ability to become actively self-directedin attention. The body model now becomes a self-model in a philosophically more interesting sense: The organism is now potentially directed at the world and at itself at the same time. It is the body as subject.
But again—who controls the focus of attention? In our Video Ergo Sum study, who is the entity misidentifying itself? Might we nevertheless have a soul, or some sort of astral body, that could survive even bodily death and experience some kind of illusory reincarnation? Will we soon achieve artificial immortality by entering into software worlds designed by human beings, through advanced Magritte-style “forbidden reproduction,” deliberately identifying ourselves with virtual bodies and virtual persons we have created for ourselves?35 Is the phenomenal world itself, perhaps, just virtual reality?
WE LIVE IN A VIRTUAL WORLD
The history of philosophy has shown that technological metaphors have considerable limitations; nevertheless, virtual reality is a useful one. Nature’s virtual reality is conscious experience—a real-time world-model that can be viewed as a permanently running online simulation, allowing organisms to act and interact.
Millions of years ago, nature’s virtual reality achieved what today’s software engineers still strive for: the phenomenal properties of “presence” and “full immersion.” From an engineering point of view, the problems involved in creating successful virtual environments are problems of advanced interface design. A virtual interface is a system of transducers, signal processors, hardware, and software. It creates an interactive medium that conveys information to the user’s senses while constantly monitoring the user’s behavior and employing it to update and manipulate the virtual environment.
Conscious experience, too, is an interface, an invisible, perfect internal medium allowing an organism to interact flexibly with itself. It is a control device. It functions by creating an internal user interface—an “as if ” (that is, virtual) reality. It filters information, has a high bandwidth, is unambiguous and reliable, and generates a sense of presence. More important, it also generates a sense of self. The self-model is much like the mouse pointer on the virtual desktop of your PC—or the little red arrow on the subway map that advises “You are here.” It places you at the center of a behavioral space, of your consciously experienced world-model, your inner virtual reality.
The Ego is a special part of this virtual reality. By generating an internal image of the organism as a whole, it allows the organism to appropriate its own hardware. It is evolution’s answer to the need for explaining one’s inner and outer actions to oneself, predicting one’s behavior, and monitoring critical system properties. Finally, it allows the system to depict internally the history of its actions as its own history. (Autobiographical memory, of course, is one of the most important layers of the human self-model, enabling us to appropriate our own history, inside-time and outside-time, the Now and the past.) Consciousness gives you flexibility, and global control gives you the Ego. On the level of conscious experience, this process of functionally appropriating one’s hardware—one’s body—in a holistic fashion is mirrored as the sense of global ownership, or minimal selfhood.
Nature, it seems, was engaged in advanced interface design long before we were. It is interesting to note that the best theorists researching virtual environments today not only employ philosophical notions such as “presence” or “situatedness” but also talk about the “virtual body.”36 For them, a virtual body is part of an extended virtual environment. It is a tool that functions much like the little red arrow or the mouse pointer. If the virtual body is employed as an interface, it can even be used to control a robot at a distance. The related concept of a “slave robot” is particularly interesting. To achieve such telepresence, there must be a high correlation between the human operator’s movements and the actions of the slave robot. (Recall the monkey controlling the robot arm? Now monkeys can even remote-control the real-time walking patterns of humanoid robots halfway around the world, from Duke University in America to the Computational Brain Project of the Japan Science and Technology Agency in Japan, and through a recording of their brain activity only. As Professor Miguel Nicolelis reports, “The most stunning finding is that when we stopped the treadmill and the monkey ceased to move its legs, it was able to sustain the locomotion of the robot for a few minutes—just by thinking—using only the visual feedback of the robot in Japan.”)37
Ideally, a human operator would identify his or her own body with that of the slave robot, achieving this with the help of the virtual body, which functions as an interface. Again, nature did just that millions of years ago: Like a virtual body, the phenomenal self-model is an advanced interface designed to appropriate and control a body. Whereas in the case of the virtual body, the slave robot may be thousands of miles away, in the case of the Ego, the target system and the simulating system are identical: The conscious experience of being a subject arises when a single organism learns to enslave itself.
The emergence of an Ego Tunnel created a much more efficient way of controlling one’s body. Controlling one’s body meant controlling one’s behavior and one’s perceptual machinery. But it also meant directing one’s thoughts and regulating one’s emotional states. The integrated conscious self-model is a special region of the high-dimensional user interface that emerged in our brains. It is a particularly user-friendly interface, allowing a biological organism to direct its attention to a critical subset of its own global properties. Having a self-model is like adaptive user-modeling, except that it is self-directed and taking place internally. In an important sense, the resulting Ego is a fiction; however, it is also a wonderfully efficient control device. You could also say that it is an entirely new window on reality.
I claim that phenomenal first-person experience and the emergence of a conscious self are complex forms of virtual reality. A virtual reality is a possible reality. As anyone who has worn a head-mounted display or played modern video games knows, we can sometimes forget the “as if ” completely—the possible can be experienced as the real. In a way, the conscious parts of our brains are like the body’s head-mounted display: They immerse the organisms in a simulated behavioral space.
Together, the embodied brain and the PSM, the phenomenal self-model, work much like a total flight simulator. Before we get to the little word “total,” let’s look at why a flight simulator is a good metaphor for the way our consciousness works. A flight simulator is, of course, a training device that helps pilots learn to control an airplane successfully. To achieve this, the simulation must be as accurate as possible in integrating two different sources of sensory information: vision and the proprioceptive sense of balance. During a simulated takeoff, for example, the pilot not only has to see the runway, but he also has to feel the acceleration of the “as if ” plane—and in relation to his own body.
Advanced flight simulators have replaced the movable cockpit mock-up and computer screen with a head-mounted display; two slightly displaced monitors create three-dimensional surround graphics. A special programming technique called infinity optics allows the pilot to look at remote objects “through the windows” of the cockpit, even though the computer-generated images are only a few inches from his face. The mock-up’s movable platform has been replaced with seat shakers that simulate a range of realistic kinesthetic sensations, such as acceleration or turbulence. Moreover, so the pilot can learn to use on-board instruments and get to know how the aircraft will react to different operations, the simulations of visual and kinesthetic input are constantly updated at great speed and with maximum accuracy.
The human brain can be compared to a modern flight simulator in several respects. Like a flight simulator, it constructs and continuously updates an internal model of external reality by using a continuous stream of input supplied by the sensory organs and employing past experience as a filter. It integrates sensory-input channels into a global model of reality, and it does so in real time. However, there is a difference. The global model of reality constructed by our brain is updated at such great speed and with such reliability that we generally do not experience it as a model. For us, phenomenal reality is not a simulational space constructed by our brains; in a direct and experientially untranscendable manner, it is the world we live in. Its virtuality is hidden, whereas a flight simulator is easily recognized as a flight simulator—its images always seem artificial. This is so because our brains continuously supply us with a much better reference model of the world than does the computer controlling the flight simulator. The images generated by our visual cortex are updated much faster and more accurately than the images appearing in a head-mounted display. The same is true for our proprioceptive and kinesthetic perceptions; the movements generated by a seat shaker can never be as accurate and as rich in detail as our own sensory perceptions.
Finally, the brain also differs from a flight simulator in that there is no user, no pilot who controls it. The brain is like a total flight simulator, a self-modeling airplane that, rather than being flown by a pilot, generates a complex internal image of itself within its own internal flight simulator. The image is transparent and thus cannot be recognized as an image by the system. Operating under the condition of a naive-realistic self-misunderstanding, the system interprets the control element in this image as a nonphysical object: The “pilot” is born into a virtual reality with no opportunity to discover this fact. The pilot is the Ego. The total flight simulator generates an Ego Tunnel but is completely lost in it.
If the virtual self functions extremely well, the organism using it is completely unaware of its “as if ” nature. The self-model activated in the human brain has been optimized over millions of years. The process that constructs it is fast, reliable, and has a much higher resolution than any of today’s virtual-reality games. As a result, the virtuality of the phenomenal self-model tends to be invisible to its user. But strictly speaking, it is simply the best hypothesis the system has about its own current state—presented in a new, highly integrated data format. To illustrate this point, let’s look at a classic experiment in modern neuropsychology.
Following amputation, many patients experience a so-called phantom limb at some point—the persistent and unmistakable impression that the lost limb is still present, still part of their body.38 These phantom limbs feel somewhat less real than the rest of the body, a bit “ghostly.” Silas Weir Mitchell, the American neurologist who introduced the concept of phantom limbs in 1871, spoke of “ghostly members” haunting people like “unseen ghosts of the lost part.”39 Often, the phantom recedes gradually and finally disappears; in some cases, however, phantom limbs can persist for months or even years. Patients often have painful sensations in their phantom limb. Sometimes, as in the now-classic case soon to be described, the phantom is “paralyzed,” creating the subjective impression that the absent limb is frozen in a fixed position and cannot be moved.
In a set of experiments involving a patient with a paralyzed phantom limb, V. S. Ramachandran and his UCSD colleagues demonstrated the virtuality of the bodily self-model.40 They constructed a “virtual-reality box” to show to what extent the content of the self-model depends on perceptual-context information. Their idea was that by manipulating the perceptual-context information—which in turn constrains the information-processing activity in the brain—the content of the bodily self-model can be changed.
Their virtual-reality box was quite simple. A mirror was placed vertically inside a cardboard box open at the top, and two holes were cut in the front of the box, to either side of the mirror. The experimenters asked Philip, a patient who had been suffering from a paralyzed phantom limb for many years, to insert both of his arms—that is, his right arm and his left “phantom arm”—through the holes in the box. Then he was told to observe the reflection of his real hand in the mirror. The mirror image of his right hand was used to create the visual illusion that he did actually have two hands. Next, he was asked to make symmetrical movements with both his real arm and his phantom arm.
What would happen to the content of Philip’s self-model if the imagined movements of his phantom arm were simultaneously matched with visual input? What would happen to his paralyzed phantom if he could see the movements of a hand in the mirror? Ramachandran described the outcome:
I asked Philip to place his right hand on the right side of the mirror in the box and imagine that his left hand (the phantom) was on the left side. “I want you to move your right and left arm simultaneously,” I instructed.
“Oh, I can’t do that,” said Philip. “I can move my right arm, but my left arm is frozen. Every morning when I get up, I try to move my phantom because it’s in this funny position and I feel that moving it might help relieve the pain. But,” he said, looking down at his invisible arm, “I never have been able to generate a flicker of movement in it.”
“Okay, Philip, but try anyway.”
Philip rotated his body, shifting his shoulder, to “insert” his lifeless phantom into the box. Then he put his right hand on the other side of the mirror and attempted to make synchronous movements. As he gazed into the mirror, he gasped and then cried out, “Oh, my God! Oh, my God, doctor! This is unbelievable. It’s mind-boggling!” He was jumping up and down like a kid. “My left arm is plugged in again. It’s as if I’m in the past. All these memories from years ago are flooding back into my mind. I can move my arm again. I can feel my elbow moving, my wrist moving. It’s all moving again.”
After he calmed down a little I said, “Okay, Philip, now close your eyes.”
“Oh, my,” he said, clearly disappointed. “It’s frozen again. I feel my right hand moving, but there’s no movement in the phantom.”
Figure 13: Mirror-induced synesthesia. Making part of a hallucinated self available for conscious action control by installing a virtual source of visual feedback. Picture courtesy of V. S. Ramachandran.
“Open your eyes.”
“Oh, yes. Now it’s moving again.”41
The phantom movement in this experiment is the content of the conscious self-model. In the real world, there is no limb that can be felt or controlled. In his moving phantom limb, Philip experiences—and controls—a part of his bodily self that does not exist. Just as in the rubber-hand illusion, the experiential property of ownership seamlessly spreads into the hallucinated part of the bodily self: The moving phantom limb is owned, just as the rubber hand is owned. On the intellectual level, Philip understands perfectly well that the phantom limb does not exist. (This fact is cognitively available to him, as a philosopher might say.) But the subjective experience of his phantom arm actually moving is robust and realistic. And, as opposed to the rubber-hand illusion, there is an additional quality—namely, the phenomenal experience of agency. A full-blown bodily Ego is in place.
In order to survive, biological organisms must not only successfully predict what is going to happen next in their immediate environment but also be able to predict accurately their behavior and bodily movements along with their consequences. The self-model is a real-time predictor. This is how our best current theories explain what happened to Philip: In our brains, we have a body emulator that uses motor commands to predict the likely proprioceptive and kinesthetic feedback that results from moving our limbs in a certain way. For our actions to be successfully controlled, we cannot wait for the actual feedback from our arms and legs as we move through the world. We need an internal image of our body as a whole that predicts the likely consequences of, say, an attempt to move our left arm in a certain way. In order to be really efficient, we need to know in advance what this would feel like. Furthermore, by “taking it offline,” we can use our body emulator to create motor imagery in our mind—to plan or imagine our body movements without actually executing them.
This body emulator, which constantly generates forward simulations, is a fundamental part of the human self-model and the centerpiece of the Ego Tunnel. Philip’s self-model had learned that whatever motor commands he issued to his amputated arm, there would be no feedback telling him about a changed limb position. To be sure, the image of his arm was still there, burned into his brain. It had adapted to zero feedback and was therefore frozen. Ramachandran’s ingenious idea was to use a mirror as a source of virtual information, allowing the virtual emulator to perform a successful update. When Philip tried to move both his real arm and his phantom arm, the changes in the visual self-model perfectly matched the motor commands fed into the body-state predictor in Philip’s brain. The conscious experience that his missing left arm was actually moving and under volitional control followed suit.
Now we can understand why our self-model is a virtual model. Clearly, Philip’s moving left arm is just a simulation. It is an “as if ” arm; what has turned into a new possibility for the brain is portrayed to Philip as a reality. If one does not think about it but simply attends to the experience itself, the moving phantom limb can perhaps be experienced as just as realistic as the rest of the body; they are both parts of the same unified self, and they are both under volitional control. But exactly how real the parts of our self-model appear depends on many different factors.
Figure 14: Evidence for an innate component of the body model? Phantoms (shaded areas) in a subject born without limbs. The numbers are vividness ratings for the felt presence of different phantom body parts on a seven-pointscale from 0 (no awareness) to 6 (most vivid impression). Picture courtesy of Peter Brugger, Zürich.
One interesting fact about phantom-limb experiences is that they also happen to people who were born missing certain limbs. A recent case study conducted by Swiss neuroscientist Peter Brugger and his colleagues of the University Hospital in Zürich used a seven-point scale to rate the subjectively perceived vividness of phantom limbs.42 Interestingly, the ratings showed highly consistent judgments across sessions for their subject, “AZ,” a forty-four-year-old university-educated woman born without forearms and legs. For as long as she could remember, she had experienced mental images of her nonexistent forearms (including fingers) and legs (including feet and the first and fifth toes). But, as the figure shows, these phantoms were not as realistic as the content of her nonhallucinatory body model.
Moreover, she reported that “[a]wareness of her phantom limbs is transiently disrupted only when some object or person invades their felt position or when she sees herself in a mirror.” Functional magnetic resonance imaging (fMRI) of her imagined phantom hand movements showed no activation of primary sensorimotor areas, but did show activity in the bilateral premotor and parietal cortex. Transcranial magnetic stimulation of the sensorimotor cortex consistently elicited sensations in the phantom fingers and hand, on the side opposite the stimulation. Premotor and parietal stimulation evoked similar phantom sensations, though without showing motor-evoked potentials in the stump. Brugger’s data demonstrate that body parts that never physically developed can be represented in sensory and motor areas of the cortex.
The fascinating question is this: Are AZ’s hallucinated forearms and legs components of an innate body model—perhaps of a nucleus that continues developing after birth? Or could they have been “mirrored into” the patient’s self-model through the visual observation of the movements of other human beings (see chapter 6 on the Empathic Ego)? What exactly is it that you feel as your own body, right now, as you are reading these words? At this point in our investigations into consciousness, it seems obvious that we are never in direct contact with our physical bodies but rather with a particular kind of representational content. But what exactly is it that is represented in this layer of our conscious self? In the second book of his famous work De anima, Aristotle said that the soul is simply the form of the body and that it perishes at death. Is that what we have newly rediscovered by studying phantom limbs, the “inner form” of the body and the global model of its shape? Spinoza said the soul is the idea that the body develops of itself because “the object of our soul is the body as it exists, and nothing else.” 43 Again, it is intriguing to see how classical philosophical ideas contribute to a deeper understanding of what it means to be an embodied self.
Ramachandran’s and Brugger’s experiments demonstrate that the experiential content of the bodily self-model is the content of an ongoing simulation, part of a dynamic control mechanism. At any given time, the content of bodily experience is the best hypothesis that the system has about its current body state. The brain’s job is to simulate the body for the body and to predict the consequences of the body’s movements, and the instrument it uses is the self-model. This process takes place in the real world, so it is time-consuming and necessarily generates a lag between the actual state of the body and the self-model’s content.
Normally we’re unaware of this process, because nature engineered it so efficiently that errors rarely occur. But the simple fact remains: You are never in direct contact with your own body. What you feel in the rubber-hand illusion, what AZ feels, or what Philip feels when his left arm is “plugged in” is exactly the same as what you feel when you attend to the sensation of your hands holding this book right now or to the feeling of pressure and resistance when you lean back in your chair. What you experience is not reality but virtual reality, a possibility. Strictly speaking, and on the level of conscious experience alone, you live your life in a virtual body and not in a real one. This point will become clearer when we consider “offline states” in the chapter on dreaming and lucid dreaming. But first, let us have a look at another essential feature of phenomenal selfhood—the transition from ownership to agency.