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-ornothing
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.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. 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 sandalwoodamber,
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 apricotpink
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 higherdimensional
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 statespace
of human Technicolor phenomenology. 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. 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.
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