Susan Blackmore goes in search of her 'self' and finds that it may just be part of the 'other'.

Why am I here? Who am I anyway? Why does everything feel, look and hurt like this? I have been asking questions such as these (or they have been asking me) ever since I can remember. For many years I thought I could find out by pursuing the paranormal - a fruitless task if ever there was one. Now the questions seem to converge on one big question: what is consciousness?

The problem of consciousness is real, and deep, and not quite like any other. I fell happily into it yesterday, walking high on the Devon cliffs, with the seagulls crying overhead. The grass brushing against my boots was so, well, grassy. It was green and lush and glistening and changing all the time as I strode along. This grassiness was my experience. Only I had exactly that vision from exactly that point of view. Yet - and here is the problem - I also believe that there is real green grass growing on that cliff; that I have objectively real eyes that take in light; and objectively existing brain cells in my head that make me see. But how can this be? How can objective things such as brain cells produce subjective experiences such as the feeling that "I" am striding through the grass?

This gap is what the Australian philosopher David Chalmers calls "the hard problem". Victorian thinkers called it the "great chasm" or the "fathomless abyss". It is a modern version of the ancient mind-body problem - but it seems to get worse, not better, the more we learn about the brain. Neuroscience is rapidly explaining how brains discriminate colours, solve problems and organise actions - but the hard problem remains. The objective world out there, and the subjective experiences in here, seem to be totally different kinds of thing. Asking how one produces the other seems to be a nonsense.

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This is what makes the problem of consciousness so interesting - and so painful. If you do not find it painful (and I will not apologise for wanting you to), pick up any object, such as a cup of tea or a pen, and just look. Do you believe there is a real cup there? Are you not also having a private subjective experience of the cup? How can this be? Call me a masochist, but I like to induce this kind of pain in myself many times every day.

The intractability of this problem suggests to me that we are making a fundamental mistake in the way we think about consciousness - perhaps right at the very beginning. So where is the beginning? For William James - whose 1890 Principles of Psychology is deservedly a classic - the beginning is our undeniable experience of the "stream of consciousness"; that unbroken, ever-changing flow of ideas, perceptions, feelings and emotions that make up our lives. These thoughts and feelings flow by and "I" experience them as they pass. This "stream" seems to be what needs explaining.

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But what if it isn't like that? What if there is no stream? Can we even conceive of this possibility? Some recent experimental results suggest we might have to.

These experiments reveal what is called "change blindness". Imagine you are looking at a complex scene - perhaps a street you can see from your window. You probably imagine that in your stream of consciousness is a rich and detailed representation of the trees and cars and people and buildings outside. Many times a second you move your eyes or blink, but the picture seems to stay there. You probably imagine that if something changed, you would notice the difference. You are probably wrong.

In change blindness experiments, a scene like this is shown to people but, by using clever eye trackers or other techniques, something in the picture is changed at the exact moment when they move their eyes. For example, a tree might disappear, a couple appear on the pavement, or a car swapped for a van. In my own experiments, and many others, people typically fail to detect the change.

This is weird. If the change is made when their eyes are still, people notice it immediately. This is because we have special detectors in the brain designed to notice objects that move and draw our attention to them. But these detectors cannot work when the whole eye moves. If the change happens to an object they are directly attending to, they notice it too, but otherwise it is as if nothing happened.

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This peculiar effect cannot be dismissed as a quirk of lab conditions. Dan Simons, at Harvard University, showed the same effect in disturbingly ordinary situations. An experimenter approached a student on the campus and asked for directions. Meanwhile, two men picked up a door and carried it between the experimenter and the student as they talked. Hidden behind the door was a second experimenter who jumped up and took the place of the first. So now the poor student was talking to a completely different person. Amazingly, most of the time the students did not notice the substitution, but just went on giving directions as before.

The conclusion seems to be this. We do not have in our heads a rich, stable and detailed visual image of the world at all. At any time we see in detail only the tiny area we are looking at. When we move our eyes, the detail is all thrown away, leaving at most a sketchy memory of the scene. We think it is all in our stream of consciousness because if ever we forget something, we can just look again and there it is. We can use the outside world as a memory, so our brains do not need to keep the details. This way we get the illusion that the details are always there. This alone shows we are wrong about our stream of consciousness.

This has been called the Grand Illusion theory, but why should we suffer such an illusion? The answer may simply be that there is too much information out there for the brain to keep it all: think of how much computer memory a single picture takes up. But the illusion is deeper still.

Have you had this experience? The phone rings, or the clock chimes, several times before you notice it. At that point you can distinctly count the number of chimes since it started - chimes you did not consciously hear. Or what about this? You drive a familiar route and on arriving at your destination remember nothing of all those lights you stopped at, pedestrians you avoided and decisions you made. Obviously you were behaving extremely intelligently, otherwise you would be dead, but somehow "you" were elsewhere - listening to Radio 4 perhaps, or chatting with a passenger. At any point in this journey you might have suddenly woken up, as it were, and been sure that you had been perfectly conscious for the past few minutes. The odd occasions are when this does not happen and you realise how long the blank must have been. This suggests to me that we live our ordinary lives in a kind of daze. From time to time, something wakes us up. In that moment of awakening the brain concocts, from memory, a backwards story about what we were just experiencing. A stream of consciousness, and a self who observes it both appear together - and both are illusions. Illusion is the right word. An illusion is something that exists, but is not what it seems. So the "me" that seems to be steadily experiencing this world is not nothing, but nor is it the persistent observer with consciousness and free will that it seems to be.

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How can I say that "I" am an illusion? Surely I, Sue Blackmore, must have a self like you do? Well, yes and no. After decades of thinking about it, funny things happen to the sense of self. Not only have I struggled with the results of experiments such as these, and practised living without free will, but I have spent a lot of time sitting still and watching. The harder you look for the self who is experiencing things, the less obviously it exists. Indeed, there can arise states in which self and other are not separate at all. This is hard to describe, but obvious when it happens. I think we have a long way to go to see through these illusions, but this is what we have to do. We need both to carry out careful experiments and to practise looking determinedly into the nature of experience itself. Perhaps then we will not see a stream of consciousness and a self who experiences it but how things really are. Only then will the hard problem disappear and the fathomless abyss close up.

Susan Blackmore, reader in psychology, University of the West of England.

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