“The word consciousness, as we use it in everyday speech, is loaded with fuzzy meanings, covering a broad range of complex phenomena. Our first task, then, will be to bring order to this confused state of affairs. We will have to narrow our subject matter to a definite point that can be subjected to precise experiments. As we will see, the contemporary science of consciousness distinguishes a minimum of three concepts: vigilance—the state of wakefulness, which varies when we fall asleep or wake up; attention—the focusing of our mental resources onto a specific piece of information; and conscious access—the fact that some of the attended information eventually enters our awareness and becomes reportable to others.

“What counts as genuine consciousness, I will argue, is conscious access—the simple fact that usually, whenever we are awake, whatever we decide to focus on may become conscious. Neither vigilance nor attention alone is sufficient. When we are fully awake and attentive, sometimes we can see an object and describe our perception to others, but sometimes we cannot—perhaps the object was too faint, or it was flashed too briefly to be visible. In the first case, we are said to enjoy conscious access, and in the second we are not (and yet as we shall see, our brain may be processing the information unconsciously).

“In the new science of consciousness, conscious access is a well-defined phenomenon, distinct from vigilance and attention. Furthermore, it can be easily studied in the laboratory. We now know of dozens of ways in which a stimulus can cross the border between unperceived and perceived, between invisible and visible, allowing us to probe what this crossing changes in the brain.

“Conscious access is also the gateway to more complex forms of conscious experience. In everyday language, we often conflate our consciousness with our sense of self—how the brain creates a point of view, an “I” that looks at its surroundings from a specific vantage point. Consciousness can also be recursive: our “I” can look down at itself, comment on its own performance, and even know when it does not know something. The good news is that even these higher-order meanings of consciousness are no longer inaccessible to experimentation. In our laboratories, we have learned to quantify what the “I” feels and reports, both about the external environment and about itself. We can even manipulate the sense of self, so that people may have an out-of-body experience while they lie inside a magnetic resonance imager.

“Some philosophers still think that none of the above ideas will suffice to solve the problem. The heart of the problem, they believe, lies in another sense of consciousness, which they call “phenomenal awareness”: the intuitive feeling, present in all of us, that our internal experiences possess exclusive qualities, unique qualia such as the exquisite sharpness of tooth pain or the inimitable greenness of a fresh leaf. These inner qualities, they argue, can never be reduced to a scientific neuronal description; by nature, they are personal and subjective, and thus they defy any exhaustive verbal communication to others. But I disagree, and I will argue that the notion of a phenomenal consciousness that is distinct from conscious access is highly misleading and leads down a slippery slope to dualism. We should start simple and first study conscious access. Once we clarify how any piece of sensory information can gain access to our mind and become reportable, then the insurmountable problem of our ineffable experiences will disappear.”