part one: toward a science of consciousness

“Consciousness: that annoying time between naps,” read the bumper sticker on a dusty SUV with California plates. It was barely nine AM, and the Arizona sun was already scorching as I made my way across the sprawling parking lots surrounding the Tucson Conference Center. On the heels of an unusually cold New England winter, I had come to the desert prepared for a reprieve, but in my long sleeves, I was still overdressed. A nondescript southwestern city, Tucson seemed an unlikely place for the cutting-edge conference on consciousness studies. But for those in the know, it is here that every other year for the past decade the brightest minds in mind science have gathered in pursuit of “a science of consciousness.”

If ten years sounds like a short record for the defining conference in a major scientific field, it only owes to the fact that the notion that something as ineffable as consciousness can be scientifically studied is itself a relatively new idea. Having built its empire on the pursuit of the third-person “objective” perspective, science in general has long considered consciousness or subjective experience to be, at best, beyond the scope of its inquiry, and, at worst, irrelevant. There was a period in the early days of psychology, when William James and other introspectionists made a foray into the subjective domain by beginning to observe and chronicle the workings of their own minds. But this was quickly expelled from the discipline by James B. Watson's introduction of behaviorism in the early 1900s, which promised to make psychology a respectable science by limiting it to the study of observable behavior. With the birth of cognitive psychology in the 1960s, and the subsequent decline of behaviorism, gradually the word “consciousness” began to trickle back into play. It wasn't until the early 1990s, however, that it would emerge as a serious area of study in its own right, due in large part to the increasing boldness of neuroscientists like Francis Crick. In an influential 1990 paper cowritten with his research partner Christof Koch, Crick, who had been determined from an early age to disprove the existence of God and the soul, made a passionate call for neuroscience to begin employing its growing scientific arsenal to demonstrate the material basis of consciousness. The paper was apparently a mark of the times, as, over the next few years, the field of consciousness studies surged into being, culminating in the inauguration of the first Tucson conference in 1994.

If the scene surrounding the opening plenary at the 2004 conference was any indication, in the ten years since, consciousness has become a hot topic. As I made my way into the conference center's largest ballroom, some eight hundred chairs faced a large video screen and stage, and cameramen jockeyed for position. Though the main section was already filled by the time I arrived, I managed to find a lone seat up front just as the conference organizer, MC, and resident bad-boy David Chalmers took the stage. Sporting faded jeans, a half-tucked-in T-shirt, black leather jacket, and scraggly long hair, the 39-year-old Australian would have been more convincing as a heavy metal singer than as one of the world's most respected philosophers of mind. But ever since the 1994 conference, when he famously challenged the audience to face up to the “hard problem” of consciousness, it's been difficult to read anything on the relationship between mind and brain without encountering Chalmers' name.

The “hard problem,” as Chalmers defines it, “is the question of how physical processes in the brain give rise to subjective experience.” This is as distinguished from the “easy problems” of consciousness, which involve understanding such things as the neural mechanisms behind perception, how we pay attention, and the differences between waking and sleep. The essence of Chalmers' challenge, which has seemingly been taken seriously by nearly everyone in the field, is that making progress on the “easy problems,” as worthy an endeavor as that might be, does not necessarily bring us any closer to solving the hard problem. And where a scientific understanding of consciousness is concerned, the hard problem is the problem.

Those who studied a bit of philosophy in college may recognize in Chalmers' hard problem a restatement of the classic “mind/body problem”—what Schopenhauer called “the world knot”—that philosophers have been arguing about over the past few centuries. Ever since René Descartes gave birth to dualism by asserting the separation of mind and body, the big issue in the philosophy of mind has been figuring out how these two different substances—the mental and the physical—could interact with one another. On one hand, how could an objective, physical brain give rise to subjective, mental events? And on the other, how could those subjective, mental events—presumably not governed by physical laws—impact the objective, physical world?

The title of the opening session, and the theme for the conference as a whole, was “Neural Correlates of Consciousness,” or NCCs, as they would come to be called. After a few welcoming words from Chalmers, we moved straight to our panel of three speakers, who would address what many consider to be the leading edge of the neurobiological approach to consciousness. The first speaker was, fittingly, Christof Koch, whose work with Francis Crick on vision and consciousness has made him one of the stars of the neuroscience world. With a delivery style that seemed to suggest he'd failed to heed the warnings about mixing high doses of caffeine with amphetamines, Koch proceeded to cram what seemed to be an entire semester of lecture notes into a thirty-minute session. I must confess to not having understood a word of it, but after concentrating as hard as I could on the next two panelists and listening to the often contentious debate that followed, I was able to piece together the rough outlines of the theory.

What Koch and other neurobiologists on the trail of NCCs are attempting to uncover is just how the brain behaves differently on the neuronal level when we are consciously perceiving something as opposed to when we are perceiving that same object unconsciously. Now, for most of us, the notion that we even could perceive something unconsciously probably sounds like an oxymoron. To illustrate, Koch refers to a curious and rather counterintuitive phenomenon known as “binocular rivalry.”

A simple explanation would go something like this: Although most of us tend to think of ourselves as somehow looking out at the world through our eyes, the nature of vision is not at all as we experience it. What is actually happening is that two different inverted two-dimensional images are falling on the back of your two retinas and being sent to some thirty different visual centers in your brain for processing, the result of which, mysteriously, is the unified three-dimensional picture of the world you see. How that happens is an example of what is known as “the binding problem” and is itself a mystery that no one has yet solved convincingly. For the moment, though, what's important to understand is that each of your eyes is seeing a different part of the picture, and your brain is piecing it together into a unified whole.

Now what happens if we isolate your eyes from one another and literally show each of them an entirely different picture? Will you see two things at once? No. This is where binocular rivalry comes in. As it turns out, your brain can only consciously represent one complete picture at a time, so when it is given two competing visual stimuli, it has to somehow choose which one to represent. At times it fixes on one image and ignores the other. Or, with the right sequence of images, it can be made to flip back and forth between the two. The key here in terms of consciousness is that regardless of which image is in consciousness at any given moment, the input into the visual centers in the brain is identical. The reason this is so exciting for Koch and his comrades is that, through the use of brain imaging techniques, it allows them to compare snapshots of the brain when a given perception is conscious and when it is not conscious. This, they hope, will ultimately give them some clues to understanding how neuronal activity correlates with consciousness.