The Ego Tunnel: The Science of the Mind and the Myth of the Self - Thomas Metzinger (2009)



Consciousness is the appearance of a world. The essence of the phenomenon of conscious experience is that a single and unified reality becomes present: If you are conscious, a world appears to you. This is true in dreams as well as in the waking state, but in dreamless deep sleep, nothing appears: The fact that there is a reality out there and that you are present in it is unavailable to you; you do not even know that you exist.

Consciousness is a very special phenomenon, because it is part of the world and contains it at the same time. All our data indicate that consciousness is part of the physical universe and is an evolving biological phenomenon. Conscious experience, however, is much more than physics plus biology—more than a fantastically complex, dancing pattern of neural firing in your brain. What sets human consciousness apart from other biologically evolved phenomena is that it makes a reality appear within itself. It creates inwardness; the life process has become aware of itself.

Judging from the available data on animal brains and evolutionary continuity, the appearance of worlds in biological nervous systems is a recent phenomenon, perhaps only a few million years old. In Darwinian evolution, an early form of consciousness might have arisen some 200 million years ago in the primitive cerebral cortices of mammals, giving them bodily awareness and the sense of a surrounding world and guiding their behavior. My intuition is that birds, reptiles, and fish have long had some sort of awareness too. In any case, an animal that cannot reason or speak a language can certainly have transparent phenomenal states—and that is all it takes to make a world appear in consciousness. Such well-known consciousness researchers and theoretical neurobiologists as Anil Seth, Bernard Baars, and D. B. Edelman have established seventeen criteria for brain structures subserving consciousness, and the evidence for the existence of such structures not only in mammals but also in birds and potentially in octopi is overwhelming. The empirical evidence for animal consciousness is now far beyond any reasonable doubt.1 Like us, animals are naive realists, and if they have, say, color sensations, it is plausible to assume that these appear to them with the same quality of directness, certainty, and immediacy as they do to us. But the philosophical point is that we really do not know. These are exactly the sort of questions we can consider only after we have constructed a satisfactory theory of consciousness.

A much more recent phenomenon emerged only a couple of thousand years ago—the conscious formation of theories in the minds of human philosophers and scientists. Thus the life process became reflected not only in conscious individual organisms but also in groups of human beings trying to understand the emergence of self-conscious minds as such—that is, what it means that something can “appear within itself.” The most fascinating feature of the human mind, perhaps, is not simply that it can sometimes be conscious, or even that it allows for the emergence of a PSM. The truly remarkable fact is that we can also attend to the content of our PSM and form concepts about it. We can communicate about it with one another, and we can experience this as our own activity. The process of attending to our thoughts and emotions, to our perceptions and bodily sensations, is itself integrated into the self-model. This property, as noted, probably distinguishes us from most other animals on this planet: the ability to turn the first-person perspective inward, to explore our emotional states and attend to our cognitive processes. As philosophers say, these are “higher-order” levels of the PSM. They allowed us to become aware of the fact that we are representational systems.

Over the centuries, the theories we have devised have gradually changed our image of ourselves, and in so doing they have subtly altered the contents of consciousness. True, consciousness is a robust phenomenon; it doesn’t change simply because of the opinions we have about it. But it does change through practice (think of wine connoisseurs, perfume designers, musical geniuses). Human beings in other historical epochs—during the Vedic period of ancient India, say, or during the European Middle Ages, when God was still perceived as a real and constant presence—likely knew kinds of subjective experience almost inaccessible to us today. Many deep forms of conscious self-experience have become all but impossible due to philosophical enlightenment and the rise of science and technology—at least for the many millions of well-educated, scientifically informed people. Theories change social practice, and practice eventually changes brains, the way we perceive the world. Through the theory of neural networks, we have learned that the distinction between structure and content—between the carrier of a mental state and its meaning—is not as clear-cut as is often assumed. Meaning does change structure, though slowly. And the structure in turn determines our inner lives, the flow of conscious experience.

In the early 1970s, after the heyday of behaviorism, interest in consciousness as a serious research topic began to rise. In several scientific disciplines, the topic of subjective experience gradually became a secret research frontier. Then, in the last decade of the twentieth century, a number of eminent neuroscientists accepted consciousness as a proper target for rigorous research. Now things developed very quickly. In 1994, after a conference of consciousness researchers in Tucson, Arizona, I helped found a new organization, the Association for the Scientific Study of Consciousness (ASSC), which is aimed at drawing together the more rigorous researchers in science and philosophy. The number of conferences and journal articles increased steeply.2 The following year, I edited a collection of philosophical articles entitled Conscious Experience .3 When one of my ASSC cofounders, Australian philosopher David Chalmers, and I compiled the bibliography, spanning the period 1970-1995, it contained about a thousand entries. Ten years later, when I updated this bibliography for the fifth German edition, it had almost twenty-seven hundred entries. At this point, I gave up my attempt to include all of the new literature on consciousness; it was simply no longer possible. The field is now well established and developing steadily.

In the meantime, we have learned many lessons. We have learned how great the fear of reductionism is, in the humanities as well as among the general public, and how immense the market is for mysterianism. The straightforward philosophical answer to the widespread fear that philosophers or scientists will “reduce consciousness” is that reduction is a relationship between theories, not phenomena. No serious empirical researcher and no philosopher wants to “reduce consciousness”; at best, one theory about how the contents of conscious experience arose can be reduced to another theory. Our theories about phenomena change, but the phenomena stay the same. A beautiful rainbow continues to be a beautiful rainbow even after it has been explained in terms of electromagnetic radiation. Adopting a primitive scientistic ideology would be just as bad as succumbing to mysterianism. Furthermore, most people would agree that the scientific method is not the only way of gaining knowledge.

But this is not the whole story. Frequently, a deeper, unarticulated insight may lie behind our uneasiness with reductive approaches to the conscious mind. We know that our beliefs about consciousness can subtly change what we perceive, influencing the very contents and functional profile of subjective experience itself. Some fear that a materialistic disenchantment, along with advances in the sciences of the mind, may have unwanted social and cultural consequences. As I point out in the concluding chapters of this book, these voices are absolutely right: This is an important aspect of the development of the mind sciences. We have learned that consciousness—like science itself—is a culturally embedded phenomenon.

We have also come to understand that consciousness is not an all-or-nothing affair, a phenomenon that either does or does not exist. It is a graded phenomenon and comes in many different shades. Consciousness is also not a unitary phenomenon but has many discernible aspects: memory, attention, feelings, the perception of color, self-awareness, and higher-order thought. Nevertheless, the essence of the phenomenon—what I call the appearance of a world—seems to be preserved throughout. One of the essential features of consciousness is that it situates you in this world. When you wake up in the morning, you experience yourself as existing at a specific time, at a single location, and embedded in a scene: A single and integrated situation emerges. The same is true for dreams or hallucinations, in which you not only experience yourself but also experience yourself in the context of a particular situation, as part of a world that has just appeared. We have learned that consciousness reaches down into the animal kingdom .4 We have learned about psychiatric disorders and brain lesions, about coma and minimally conscious states, about dreams, lucid dreams, and other altered states of consciousness. All this has led to a general picture of a complex phenomenon that comes in different flavors and strengths. There is no single on-off switch. The fact that consciousness is a graded phenomenon sometimes causes conceptual problems. At the same time, we are already beginning to find the first neural correlates of specific forms of conscious content.5 Eventually we should be able to discern the minimal set of properties our brains require to activate specific qualities of experience, such as the apricot-pink color of the evening sky or the scent of amber and sandalwood.

However, what we do not know is how far discovering such neural correlates will go toward explaining consciousness. Correlation is not causation, nor is it explanation. And if certain aspects of consciousness are ineffable, we obviously cannot correlate them with states in our brains. We have no good understanding of what it means to say that consciousness is “subjective,” a “private” phenomenon tied to individual selves. But pinning down the neural correlates of specific conscious contents will lay the foundation for future neurotechnology. As soon as we know the sufficient physical correlates of apricot-pink or sandalwood-amber, we will in principle be able to activate these states by stimulating the brain in an appropriate manner. We will be able to modulate our sensations of color or smell, and intensify or extinguish them, by stimulating or inhibiting the relevant groups of neurons. This may also be true for emotional states, such as empathy, gratitude, or religious ecstasy.

First things first, however. Before we can understand what the self is, we must look at the current status of consciousness science by taking a brief tour of the landscape of consciousness, with its unique complex of problems. There has been considerable progress, but as far as our conscious minds are concerned, we still live in prehistoric times. Our theories about consciousness are as naive as the first ideas cavemen probably had about the true nature of the stars. Scientifically, we are at the very beginning of a true science of consciousness.

The conscious brain is a biological machine—a reality engine—that purports to tell us what exists and what doesn’t. It is unsettling to discover that there are no colors out there in front of your eyes. The apricot-pink of the setting sun is not a property of the evening sky; it is a property of the internal model of the evening sky, a model created by your brain. The evening sky is colorless. The world is not inhabited by colored objects at all. It is just as your physics teacher in high school told you: Out there, in front of your eyes, there is just an ocean of electromagnetic radiation, a wild and raging mixture of different wavelengths. Most of them are invisible to you and can never become part of your conscious model of reality. What is really happening is that the visual system in your brain is drilling a tunnel through this inconceivably rich physical environment and in the process is painting the tunnel walls in various shades of color. Phenomenal color. Appearance. For your conscious eyes only.

Still, this is only the beginning. There is no clean one-to-one mapping of consciously experienced colors to physical properties “out there.” Many different mixtures of wavelengths can cause the same sensation of apricot-pink (scientists call these mixtures metamers). It is interesting to note how the perceived colors of objects stay relatively constant under varying conditions of illumination. An apple, for instance, looks green to us at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red with a lot of yellow. Subjective color constancy is a fantastic feature of human color perception, a major neurocomputational achievement. On the other hand, you can consciously experience the same physical property, say, the hot kitchen stove in front of you, as two different conscious qualities. You can experience it as the sensation of warmth and as the sensation of glowing red, as something you feel on your skin and as something you project into a space in front of your eyes.

Nor must your eyes be open to enjoy color experience. Obviously, you can also dream of an apricot-pink evening sky, or you can hallucinate one. Or you can enjoy an even more dramatic color experience under the influence of a hallucinogenic drug, while staring into the void behind your closed eyelids. Converging data from modern consciousness research show that what is common to all possible conscious sensations of apricot-pink is not so much the existence of an object “out there” as a highly specific pattern of activation in your brain. In principle, you could have this experience without eyes, and you could even have it as a disembodied brain in a vat. What makes you so sure you are not in a vat right now, while you’re reading this book? How can you prove that the book in your hand—or your hand itself, for that matter—really exists? (In philosophy, we call this game epistemology—the theory of knowledge. We have been playing it for centuries.)

Conscious experience, as such, is an internal affair. Whatever else may or may not be true about consciousness, once all the internal properties of your nervous system are set, all the properties of your conscious experience—its subjective content and the way it feels to you—are fully determined. By “internal” I mean not only spatial but also temporal internality—whatever is taking place right now, at this very moment. As soon as certain properties of your brain are fixed, everything you are experiencing at this very moment is also fixed.

Philosophically, this does not yet mean that consciousness can be explained reductively. Indeed, it is not clear what counts as a whole experience: Are experiences discrete, countable entities? However, the flow of experience certainly exists, and cognitive neuroscience has shown that the process of conscious experience is just an idiosyncratic path through a physical reality so unimaginably complex and rich in information that it will always be hard to grasp just how reduced our subjective experience is. While we are drinking in all the colors, sounds, and smells—the diverse range of our emotions and sensory perceptions—it’s hard to believe that all of this is merely an internal shadow of something inconceivably richer. But it is.

Shadows do not have an independent existence. And the book you are holding right now—that is, the unified sensations of its color, weight, and texture—is just a shadow, a low-dimensional projection of a higher-dimensional object “out there.” It is an image, a representation that can be described as a region in your neural state-space. This state-space itself may well have millions of dimensions; nevertheless, the physical reality you navigate with its help has an inconceivably higher number of dimensions.

The shadow metaphor suggests Book VII of Plato’s Republic. In Plato’s beautiful parable, the captives in the cave are chained down at their thighs and necks. They can only look straight ahead; their heads have been shackled in a fixed position since birth. All they have ever seen of themselves and of one another are the shadows cast on the opposite wall of the cave by the fire burning behind them. They believe the shadows to be real objects. The same is true of the shadows cast by the objects carried along above the wall behind their heads. Might we be like the captives, in that objects from some outside world cast shadows on the wall in front of us? Might we be shadows ourselves? Indeed, the philosophical version of our position on reality developed from Plato’s myth—except that our version neither denies the reality of the material world nor assumes the existence of eternal forms constituting the true objects of those shadows on the wall of Plato’s cave. It does, however, assume that the images appearing in the Ego Tunnel are dynamic projections of something far greater and richer.

But what is the cave, and what are the shadows? Phenomenal shadows are low-dimensional projections within the central nervous system of a biological organism. Let us assume that the book you are holding, as consciously experienced by you at this very moment, is a dynamic, low-dimensional shadow of the actual physical object in your actual physical hands, a dancing shadow in your central nervous system. Then we can ask: What is the fire that causes the projection of flickering shadows of consciousness, dancing as activation patterns on the walls of your neural cave? The fire is neural dynamics. The fire is the incessant, self-regulating flow of neural information-processing, constantly perturbed and modulated by sensory input and cognition. The wall is not a two-dimensional surface but the high-dimensional phenomenal state-space of human Technicolor phenomenology.6 Conscious experiences are full-blown mental models in the representational space opened up by the gigantic neural network in our heads—and because this space is generated by a person possessing a memory and moving forward in time, it is a tunnel. The pivotal question is this: If something like this is taking place all the time, why don’t we ever become aware of it?

Antti Revonsuo alluded to the fascinating phenomenon of OBEs when he compared conscious experience to a constant and effortless out-of-brain experience.7 As I have, he invokes the world-simulation model to explain why the sense of presence you are enjoying right now is only an inner, subjective kind of presence. The idea is that the content of consciousness is the content of a simulated world in our brains, and the sense of being there is itself a simulation. Our conscious experience of the world is systematically externalized because the brain constantly creates the experience that I am present in a world outside my brain. Everything we know about the human brain today indicates that the experience of being outside the brain, and not in a tunnel, is brought about by neural systems buried deep inside the brain. Of course, an external world does exist, and knowledge and action do causally connect us to it—but the conscious experience of knowing, acting, and being connected is an exclusively internal affair.

Any convincing theory of consciousness will have to explain why this does not seem so to us. Therefore, let us embark on a brief tour of the Ego Tunnel, examining some of the most important problems for a philosophically as well as neuroscientifically convincing theory of consciousness. We will discuss six of them in detail: the One-World Problem, or the unity of consciousness; the Now Problem, or the appearance of a lived moment; the Reality Problem, or why you were born as a naive realist; the Ineffability Problem, or what we will never be able to talk about; the Evolution Problem, or the question of what consciousness was good for; and finally, the Who Problem, or the issue of what is the entity that has conscious experience. We are starting with the easiest problem and ending with the hardest. After this, our groundwork will be done.