Consciousness is a subjective thing: you have your experience and I have mine, and short of one of us being psychic there is no way to compare them except by talking to each other. But even given this gulf, if enough people report on their experiences and these reports are sufficiently similar we can in good faith claim to know something objective about the structure of consciousness. For example, it is embodied. We are not everywhere at once, or five or six places. Human beings experience the world from a single vantage point that coincides with our bodies. We are one with our bodies, or at least “in” them somehow. Likewise, our consciousness has a particular orientation towards time. The past is unchangeable and the future unknown, while the outside world impinges on us through a narrow aperture we call “now”. We cannot go through time as we might wander from room to room in a house, retracing our steps at will. Instead time is like a roller coaster on which our consciousness rides, moving inexorably forward.
Clearly the challenge of elucidating a science of consciousness lies not in uncovering what is hidden, but rather in taking notice of what is so much a part of our everyday existence that we tend to overlook it. Nowhere is this more apparent than in the manifestly binary nature of consciousness, the way each of us goes through life with seemingly two parallel identities, one acting in the present moment, and the other passively reliving the experiences of the previous day.
Say I have just returned from a business trip. In in the morning I sit in my kitchen at home, drinking a cup of coffee, while at the same time I am also back in another city hundreds of miles away, having breakfast in the hotel restaurant. Both experiences are equally “real”, perceived with equal vividness on parallel tracks, as it were, though obviously only in the forward one can I exercise my free will, while in the echo I simply ride along with the decisions and contingencies of the recent past. We take this duplication so much for granted that we can scarcely imagine how it could be otherwise. Still it is worthwhile to try and suspend our everyday intuitions in order to get a clearer picture of what the echo truly is.
Why should we have only two consciousnesses? Why not three or four, staggered over the past few years? Why should the echo lag be–barring the disorienting jumble that sometimes comes with prolonged lack of sleep–always about twenty four hours? Presumably this has something to do with the human diurnal cycle, but it provides no obvious evolutionary advantage. Couldn’t we get by just as well if we were like The Least Impulsive Man in the World in the famous James Thurber story of the same name, who reexperiences his life “like clockwork” a mere fifteen minutes after it happens? For that matter, why shouldn’t we have just a single consciousness? After all, we only have one body. Why not also one mind, one “now”, experienced once, then gone forever?
Though the idea of unitary consciousness may seem deeply unsettling to us, throughout history different cultures have manifested a range of attitudes towards it. In the Tibetan Buddhist tradition, for instance, monks devote their lives to a meditation practice which has the goal of bringing the forward life and the echo together, so that there is only one experience, a solitary Now. Christians in medieval Europe believed that only the forward life was real. The echo was merely an image in God’s mind, a review in which He passed judgement on our (usually sinful) exercise of free will. As one goes further back in the historical record, the echo becomes more indistinct. In the Old Testament it is difficult to separate it from the voice of God, while in the writings of classical Greece it is hard to discern duality at all. Closer to our own time, the neurologist Oliver Sacks recounts in his classic book The Man Who Mistook His Wife for a Hat the experience of monoaphasics, people with a rare brain disorder that suppresses or even completely eliminates the echo. Contrary to what one might expect, the life of a monoaphasic is not particularly disorienting or unmoored. In fact, it is common for them to make it into their early twenties before realizing that they have a brain disorder at all.
Even assuming that our modern idea of a staggered binary consciousness is essentially correct, recent scientific research points to it being a more complicated phenomenon than we suppose it to be. Consider the question of memory. Across cultures there is consensus that whatever the echo is, it is not merely a memory of the previous day’s events. Now in a sense the echo must be a memory–it is, after all, the product of past experiences stored in the brain–nevertheless, to call it that just feels wrong. There are facts that argue in favor of this intuition. Memory is largely voluntary: we can choose to focus on this or that past event in any sequence we like. Memories also tend to be brief and indistinct. My memory of yesterday’s breakfast at the hotel is more like a collage–a coffee cup here, a buffet table there–that may cohere into the idea of the experience, but is nothing like the echo, which is that experience, replayed in precisely the same vividness and detail as when it first impressed itself on my body.
Or is it? In the past few years neuroscientists have been using fMRI brain imaging to get a clearer picture of exactly what is happening in the echo. It is possible to present people with visual and auditory stimuli that produce a distinct “signature” that shows up twice in brain images, once when it is first experienced and once, about a day later, when it echoes. This way, the journey of an experience can be tracked as it makes its way through our two selves. Using these techniques, neuroscientists have discovered that the same regions of the brain appear to be enlisted in both voluntarily recalling an event and in echoing it. Even more surprisingly, the data show the echo to be a less faithful recreation of the original experience than it seems. To the subject everything might feel smooth and coherent, but the fMRI tells a different story. Echoed events sometimes occur out of order. Something the forward self experienced for half an hour might echo by in a matter of seconds. Significant chunks of the previous day even appear to be occasionally dropped without anyone being the wiser. This is of a piece with broader findings of cognitive science, which have shown perception not to be a simple matter of taking in raw sense data but also of shaping it into a coherent form. If it is true of the perceiving edge of the forward self, why shouldn’t it be true in the echo as well?
A theory that has lately been gaining popularity among cognitive scientists posits a unitary “executive” consciousness that oversees both the forward and the echoed self, ensuring that the latter stays in sync with the former. Basically, we are all secret monoaphasics. The thought of this can be unsettling. To deny the reality of our echo is to dismiss part of our most intimate self as an illusion. Our echo is the inhibitor of our misdeeds, the amplifier of our pleasure, the thing that keeps us from feeling that life rushes by too quickly to take in, and ultimately the promise that we are not alone. It would be a mistake, though, to shrink from the insight science gives us into ourselves. Binary consciousness is in no way diminished by a glimpse of its deep neural underpinnings. If anything, understanding them only enriches the fundamental truth of our whole selves. Forward and echo: we remain who we are.