I am not going to attempt to recapitulate the arguments of The Master and his Emissary here. Those who are interested in going further into it, can read the book. But let me give some hints at what underlies hemisphere difference.
It could all be seen as stemming from a matter of attention. Attention may sound dull, but it is an essential aspect of consciousness. In fact it governs what it is that we turn out to be conscious of, and therefore plays a part in the coming into being of whatever exists for us.
What sort of thing we see in the world determines the kind of attention we pay to it. But, equally, the kind of attention we pay to anything determines what it is we find there. The human body is a perfect example. The attention paid by the physician, the lover, the mother, the anatomist, the artist, the acrobat are all, or should be, widely different. And in turn they yield widely different versions of the body in question, suggesting different purposes, values and focuses of interest in those who are attending. No-one of them is the real, the true body – which is not to say that any old view of the body would do. Each is right for some purposes. There is no privileged path into this circle of understanding: we have to make a leap, guided by experience.
And the further interpretation, or understanding, of what it is we find there similarly involves a circularity. To understand something, whether we are aware of it or not, depends on choosing a model. We get to understand what we see by comparing it with something else, something that we think we understand better. But what we compare it with turns out to have a huge influence on the outcome. Our understanding is only as good as the model we choose, and is limited by it. Thus comparing a football match to a trip to the betting shop brings out one aspect of the experience; comparing it to going to church brings out others.
This applies to how we understand the brain and the mind themselves – the means by which we understand everything else. It has to, since it applies to everything whatever. What can we compare the mind to, or the brain to, that we think we understand better? It’s not obvious. And where we don’t consciously choose a model, we in fact choose one without thinking. Nowadays that default model is the machine.
Different 'takes' on the mind reveal some aspects of it, but by the very same token conceal others. We cannot have it all at once. It is the like the duck-rabbit:
we can move between ‘takes’ – duck or rabbit – but we cannot have no take – or more than one take at once. And positive feedback means that we can easily get stuck within one way of looking at things, with resistance to any attempt to shift the type of attention we pay, or the model we use.
Now back to the hemispheres. There are reliable differences in the nature of the attention that each of the human hemispheres pays to the world, and it turns out these are already present in animals and birds.
The neurological literature conventionally distinguishes five types of attention: alertness, sustained attention, vigilance, focussed attention and divided attention. Alertness, sustained attention and vigilance, it transpires, are all better maintained by the right hemisphere: whereas focussed attention is generally better maintained by the left hemisphere (in the case of divided attention, the evidence is divided).
Why is this? The best way to understand why this divide exists is to think of a chick trying to pick out a seed against the background of grit on which it lies. It needs to be able to target precisely, with highly focussed attention, something it has already decided is of value, and to pick it out against a background of irrelevant stimuli. However, if it is to remain alive in the process, it also has to keep a sharp look out, at the same time, for the unexpected – a quite different type of attention. It needs a quite uncommitted, open attention for whatever else may be – be it mate or fate, friend or foe. This is quite a feat, two types of consciousness at once in the same brain. No wonder the brain is divided into two realms of awareness, each with its own type of attention.
The consequences of these attentional differences are profound. For one thing new experience comes from the outer edges of experience, and new experience, of whatever kind, is realised first by the right hemisphere. It is ‘present’ there - ‘presences’ there, to use a term of Heidegger’s - and only later is translated into a ‘re-presentation’ in the left. The right sees everything as in context – not just as an individual billiard ball, put together accidentally with a lot of other billiard balls, but as something which exists only in the context in which it inheres.
The right hemisphere understands what I call ‘betweenness’: not the fact of one thing being conjoined with another, nor the conjunction itself – not even the assemblage of the parts and their togetherness; but the whole thing, which involves everything being seen in the light of everything else, before any such ‘assemblage of the parts’ could take place. It sees everything as flowing, changing, and evolving, rather than fixed, static and known. It sees the living, where the left hemisphere sees the inanimate. This has important consequences for our appreciation of music, time and the evolving self.
What the left hemisphere offers is a crucial aspect of reality, that aspect which enables us to have fixity, and which therefore enables us to use and manipulate it. Without it, we could not reason in certain ways, exploit the world around us to our benefit, or have a civilisation at all. We need to be able to pin things down and ‘grasp’ them , as we say (not for nothing do most of us use the right hand, controlled by the left hemisphere, to grasp what is of use to us, and use our left hemisphere to provide that aspect of language with which we say we ‘grasp’ something). I value these aspects of our ability to engage with the world. My thesis is in fact based on the gathering of a huge amount of evidence, hard worked for by others and to a much smaller degree by myself, and depends on rational argument. We get nowhere if we disrespect or disregard systematic thinking. There is often too little, not too much, clear thinking involved in our attempts to understand the world. My argument is that we need to use what this kind of understanding gives us within a broader framework, which we can all too easily ignore, because that framework is not itself contained within, or even implied within, this way of thinking. Hence my belief is that we need both left hemisphere and right hemisphere ways of thinking. Our right hemisphere is aware of that. But the characteristic mode of the left hemisphere' s thinking makes it unaware of what it doesn't know. It thinks it can go it alone. That is where the trouble begins.
Of course these two takes on the world are not absolute. In daily life we learn somehow to combine them, probably by moving back and forth between them, without even being aware we are doing so. But they can come to compete in the realm of ideas – in philosophy, and in the history of culture. My belief is that there is a tendency, built into the way each hemisphere operates, for things to get increasingly locked into what one half of the brain only, the left half, thinks it knows. I believe this happened in the past, following a period of superbly rich co-operation between the hemispheres, in the case of late ancient Greek culture, and happened again in the case of late Roman culture, and is happening yet again in our own.
There are a number of reasons why this happens. One is that the left hemisphere’s take on reality, though very useful, is much simpler than that of the right. For example, the right hemisphere’s take on things is oblique and implicit, and it understands that a thing and its opposite may both be true, which complicates reality, to say the least. This means that the left hemisphere’s take is sometimes seductive, by reason of its very obviousness.
The great philosopher Isaiah Berlin laid out the three propositions on which the Western tradition is founded: that all genuine questions can be answered, that if a question cannot be answered it is not a question; that all these answers are knowable, that they can be discovered by means which can be learnt and taught to other persons; and that all the answers must be compatible with one another. Berlin was profoundly sceptical of them, as am I. For anyone who has lived, each of these propositions is, in fact, blatantly false. It is only being in thrall to the view of the left hemisphere that makes us consider, even for an instant, that they might be valid. The left hemisphere’s model of the world has a charming and compelling simplicity, because it has ruthlessly excised everything that does not fit its model. Having purified the world so that it fits its vision, it find its vision fits the world.
Then there is the fact that the left hemisphere is highly vocal on its own behalf. It is full of confidence in its own simple vision. What’s more, it is the Berlusconi of the brain, in the sense that it controls the media: it controls speech and constructs the argument. The right hemisphere does not have a voice – literally.
But more importantly than anything else, the left hemisphere denies the importance of what it does not understand, ignores what it cannot accommodate, ironises what it doesn’t accept, and generally pulls the rug from under the feet of those who would look to anything beyond what it has to offer. Thus the idea that the body might be anything other than a machine, along with the inherited wisdom transmitted by a historical culture, and the sense of the natural world as more than just a heap of resource, have all been relentlessly undermined in our time. Meanwhile the realm of the arts and the spiritual world have been trivialized and lost their power to convey anything to many of us.