A few weeks ago, while staying with my in-laws, my four-month-old son woke up at two-thirty in the morning. He was hungry, and, knowing that he would not be coaxed back to sleep without a bottle, I brought him downstairs to the kitchen, where his crying stopped abruptly. He clearly recognized that he had arrived in an unfamiliar place, and he became fully absorbed in understanding where he was and how he’d gotten there. He was searingly alert; he craned his head and his eyes darted around. The eight minutes or so that it took it to warm the bottle, usually a time of intense complaint, passed with hardly a peep. I became convinced that, for the first time, my son was fully, consciously aware of his surroundings.

As a scientist, I realize that my experience was subjective. But the leading scientific journal, Science, just published the results of an experiment that endeavored to look objectively at the rudiments of consciousness in infants. This work, conducted by the cognitive psychologists Sid Kouider, Stanislas Dehaene, and Ghislaine Dehaene-Lambertz, is an examination of brain waves in babies between five and fifteen months old, aimed at constructing what the scientists refer to as a “biological signature of consciousness.”

The background of this experiment is a theory called the “global workspace” model of consciousness, according to which perceptual awareness involves two stages of neural activity. The first is a purely sensory activation, typically in the back of the brain. The second stage reflects a kind of “ignition,” and is achieved only for stimuli that are consciously perceived.

The global-workspace theory rests on the fact that it is possible to see something without being aware of it. Suppose a subject is shown a picture of a face very briefly, and then, immediately afterward, shown a second image, of a different face, for a longer period of time. Her eyes and the visual portions of her brain will register the first image, but if the interval is brief enough she won’t be able to report seeing it—perception without awareness. In this case, the first characteristic set of brain waves will be present, but the second will not.

Kouider and his colleagues showed similar stimuli to infants, varying how long the first face was visible. Although they couldn’t ask infants to directly report their experiences, they found that the brain waves of fifteen-month-olds resembled those of adults, with one set occurring regardless of how long the first image was present, and a second set elicited only when it was visible for longer—likely, long enough to have made it to conscious awareness. Infants who were five months old displayed many of the rudiments of that same pattern, if a bit more slowly.

The researchers make a convincing case that infants change in important ways in the time between five to fifteen months old. It’s also clear from their data that some precursor of “perceptual” consciousness was present even in the youngest children they tested.

But what that precursor indicates is unclear. Five-month-olds may be on their way toward distinguishing relevant from irrelevant stimuli, but it is entirely possible that the second stage of brain waves is merely a prerequisite for conscious awareness—nobody knows if that second stage is consciousness, or just a key step along the way. As the scientists themselves carefully noted, “It is important to acknowledge that our research does not provide a direct proof of subjective experience.”

David Chalmers, my colleague at N.Y.U., famously distinguished between what he has called the “hard problem” and the “easy problems” of consciousness. Easy problems include, say, explaining the difference between wakefulness and sleep. The hard problem, Chalmers suggested, was that of understanding the nature of experience itself. Cognitive science and neuroscience, he argued, have yielded little insight into the subjective aspects of experience, like how we’re affected by the sound of a clarinet or what happens when we conjure up images internally.

Even if Chalmers is wrong, and consciousness turns out to be parsable with conventional scientific methods, as, for example, Daniel Dennett has argued, the problem is damn tricky. A more pessimistic view on consciousness belongs to the University of Miami philosopher Colin McGinn, a New Mysterian (so named by the philosopher Owen Flanagan for the rock band Question Mark and the Mysterians), who argues that no scientific means will ever get humans to an adequate explanation of consciousness, because evolution has not equipped our brains with the tools necessary to reckon with the phenomenon itself.

Within the sciences, McGinn’s view is increasingly seen as backward, an artifact of an earlier time when we knew less about the brain. Scientific articles in leading journals bearing on the neural basis of consciousness are now routine. More neuroscientists now see the riddle of consciousness as a fully tractable problem, something that can be dissected with tools like brain imaging and optogenetics.

In a recent book, the neuroscientist Christof Koch, now the chief scientific officer of the Allen Institute for Brain Science, recounts an irate audience member complaining about his proposal that primates other than humans might have consciousness: “You will never be able to convince me that a monkey is conscious!” she said. “And you can never convince me that you are conscious,” Koch replied. For Koch, the tools of introspection will never suffice, but the tools of neuroscience might.

As it happens, Koch, McGinn, and I will be discussing these questions on Friday, at the World Science Festival, at N.Y.U., the site of one of Woody Allen’s most famous stand-up lines: “I was thrown out of N.Y.U. in my freshman year for cheating on my metaphysics exam,” he says, because “I looked within the soul of the boy sitting next to me.” Whether we can get any further than Woody Allen could remains to be seen.

Photograph by Martin Parr/Magnum.