The one-world problem: The unity of consciousness part 1

Once upon a time, I had to write an encyclopedia article on “Consciousness.”
The first thing I did was to photocopy all existing encyclopedia articles
on the topic I could find and track down the historical references. I
wanted to know whether in the long history of Western philosophy
there was a common philosophical insight running like a thread through
humanity’s perennial endeavor to understand the conscious mind. To
my surprise, I found two such essential insights.
The first is that consciousness is a higher-order form of knowledge
accompanying thoughts and other mental states. The Latin concept of
conscientia is the original root from which all later terminologies in
English and the Romance languages developed. This in turn is derived
from cum (“with,” “together”) and scire (“to know”). In classical antiquity,
as well as in the scholastic philosophy of the Christian Middle
Ages, conscientia typically referred either to moral conscience or to
knowledge shared by certain groups of people—again, most commonly
of moral ideas. Interestingly, being truly conscious was connected to moral insight. (Isn’t it a beautiful notion that becoming conscious in the
true sense could be related to moral conscience? Philosophers would
have a new definition of the entity they call a zombie—an amoral person,
ethically fast asleep but with eyes wide open.) In any case, many of the classical theories stated that becoming conscious
had to do with installing an ideal observer in your mind, an inner
witness providing moral guidance as well as a hidden, entirely private
knowledge about the contents of your mental states. Consciousness
connected your thoughts with your actions by submitting them to the
moral judgment of the ideal observer. Whatever we may think about
these early theories of consciousness-as-conscience today, they certainly
possessed philosophical depth and great beauty: Consciousness
was an inner space providing a point of contact between the real human
being and the ideal one inside, the only space in which you could be together
with God even before death. From the time of René Descartes
(1596–1650), however, the philosophical interpretation of conscientia
simply as higher-order knowledge of mental states began to predominate.
It has to do with certainty; in an important sense, consciousness is
knowing that you know while you know.
The second important insight seems to be the notion of integration:
Consciousness is what binds things together into a comprehensive, simultaneous
whole. If we have this whole, then a world appears to us. If
the information flow from your sensory organs is unified, you experience
the world. If your senses come apart, you lose consciousness.
Philosophers like Immanuel Kant or Franz Brentano have theorized
about this “unity of consciousness”: What exactly is it that, at every single
point in time, blends all the different parts of your conscious experience
into one single reality? Today it is interesting to note that the first
essential insight—knowing that you know something—is mainly discussed
in philosophy of mind, whereas the neuroscience of consciousness
focuses on the problem of integration: how the features of objects
are bound together. The latter phenomenon—the One-World Problem
of dynamic, global integration—is what we must examine if we want to
understand the unity of consciousness. But in the process we may discover
how both these essential questions—the top-down version dis-cussed in philosophy of mind and the bottom-up version discussed in
the neurosciences—are two sides of the same coin.
What would it be like to have the experience of living in many worlds
at the same time, of genuine parallel realities opening up in your mind?
Would there be parallel observers, too? The One-World Problem is so
simple that it is easily overlooked: In order for a world to appear to us, it
has to be one world first. For most of us, it seems obvious that we live
our conscious lives in a single reality, and the world we wake up to every
morning is the same world we woke up to the day before. Our tunnel is
one tunnel; there are no back alleys, side streets, or alternative routes.
Only people who have suffered severe psychiatric disorders or have experimented
with major doses of hallucinogens can perhaps conceive of
what it means to live in more than one tunnel at a time. The unity of
consciousness is one of the major achievements of the brain: It is the
not-so-simple phenomenological fact that all the contents of your current
experience are seamlessly correlated, forming a coherent whole, the
world in which you live your life.
But the problem of integration has to be solved on several subglobal
levels first. Imagine you are no longer able to bind the various features of
a seen object—its color, surface texture, edges, and so on—into a single
entity. In a disorder known as apperceptive agnosia, no coherent visual
model emerges on the level of conscious experience, despite the fact that
all the patient’s low-level visual processes are intact. Sufferers typically
have a fully intact visual field that is consciously perceived, but they are
unable to recognize what it is they are looking at. They cannot distinguish
shapes from or match shapes with each other, for example, or
copy drawings. Apperceptive agnosia is usually caused by a lack of oxygen
supply to the brain—for instance, through carbon monoxide poisoning.
Patients may well have a coherent, integrated visual world- model,
but certain types of visual information are no longer available to them to
act upon. On a functional level, they cannot use gestalt grouping cues or
figure/ground cues to organize their visual field. Now imagine you are
no longer able to integrate your perception of an object with the categorical
knowledge that would allow you to identify it, and you consequently
cannot subjectively experience what it is you are perceiving—as in asterognosia (the inability to recognize objects by touch, typically associated
with lesions in two regions of the primary somatosensory cortex)
or autotopagnosia (the inability to identify and name one’s own
body parts, also associated with cortical lesions). There are also patients
suffering from what has been called disjunctive agnosia, who cannot integrate
seeing and hearing—whose conscious life seems to be taking
place in a movie with the wrong soundtrack. As one patient described
his experience, someone “was standing in front of me and I could see his
mouth moving, but I noticed that the mouth moving did not belong to
what I heard.”Now, what if everything came apart? There are neurological patients
with wounded brains who describe “shattered worlds,” but in these cases
there is at least some kind of world left—something that could be experienced
as having been shattered in the first place. If the unified, multimodal
scene—the Here and Now, the situation as such—dissolves
completely, we simply go blank. The world no longer appears to us.
A number of new ideas and hypotheses in the neurosciences suggest
how this “world-binding” function works. One such is the dynamical
core hypothesis, which posits that a highly integrated and internally differentiated
neurodynamic pattern emerges from the constant background
chatter of millions of neurons incessantly firing away. Giulio
Tononi, a neuroscientist at the University of Wisconsin–Madison who is
a leading advocate of this hypothesis, speaks of a “functional cluster” of
neurons, whereas I have coined the concept of causal density. The basic idea is simple: The global neural correlate of consciousness
is like an island emerging from the sea—as noted, it is a large set of neural
properties underlying consciousness as a whole, underpinning your
experiential model of the world in its totality at any given moment. The
global NCC has many different levels of description: Dynamically, we
can describe it as a coherent island, made of densely coupled relations of
cause and effect, emerging from the waters of a much less coherent flow
of neural activity. Or we could adopt a neurocomputational perspective
and look at the global NCC as something that results from informationprocessing
in the brain and hence functions as a carrier of information.
At this point, it becomes something more abstract, which we might en-vision as an information cloud hovering above a neurobiological substrate.
The “border” of this information cloud is functional, not physical;
the cloud is physically realized by widely distributed firing neurons in
your head. Just like a real cloud, which is made of tiny water droplets
suspended in the air, the neuronal activation pattern underlying the totality
of your conscious experience is made of millions of tiny electrical
discharges and chemical transitions at the synapses. In strict terms, it
has no fixed location in the brain, though it is coherent.