Philosophy loses another limb
Nicholas Fearn
THE SPACE BETWEEN OUR EARS: How THE BRAIN REPRESENTS VISUAL SPACE by Michael Horgan Weidenfeld, £20, pp. 199, ISBN 029782970X We think of our eyes as windows onto the world, but they are more like television cameras. For no matter how far away the horizon or how broad and contoured the vista we look upon, the scene is constructed from a flat image on the retina. Our sense of touch, by contrast, gives no such illusion of depth — we feel only what impresses on our palms, and no further, Our fingertips cannot penetrate the surfaces of a substance, nor would we think this possible, yet we cannot help believing sight to have just such a ghostlike power. Though it seems to extend infinitely, the universe of our visual perception is skin-tight, and the void itself begins on the other side of the cheek. However, this truth is not only disturbing but also decidedly inconvenient, as we need three-dimensional maps to negotiate our environment. Since space was not given to the mind, the mind had to create it.
How the mind (or 'brain' as we are supposed to say these days) represents space is a difficult question, but one that is beginning to be answered. As Michael Horgan explains, progress continues despite the insistence of some writers that there are no maps among the neurons. This is the thesis of 'Strong AI', the view that mentality is reducible to digital computation, and Horgan will have none of it. Instead, he contends, mentality is about analogue computation. To mystics and sentimentalists this will seem a disappointment: computation shmomputation — it's all the same robotic materialism. However, this is what the question of mind has come down to, which should really tell us that the question has essentially been answered, just as the question of the ascent of man has been settled although certain biologists disagree over some details of evolution. If it makes the mystics feel any better, analogue computation at least gives the mind a more direct relationship with the world, our analogue neural network, as the name would suggest, being
analogous in some way to the lines and forms we see around us. The mind represents the world by being like it, to some extent. Admittedly, a brain scan of someone perceiving redness will not reveal any red pigment in the visual cortex, but neither would one find water in the wheels and pulleys of the machine Lord Kelvin built in 1872 to compute tide levels for many years hence. What made the latter effective was the analogous relationship between sea-levels and the rise and fall of a point on the circumference of a turning wheel. What will not make the mystics feel better is that the notion of affinities between the inner world and the outer is not to be taken superstitiously. They are nature's solution to an engineering problem, not the result of any oneness of all creation.
The author lashes philosophers for pronouncing on the mind without any knowledge of scientific facts, but his own account is descended from the philosopher Immanuel Kant's realisation that perception is a form of action. What Kant never knew was how varied are the lengths to which the brain goes on our behalf. Horgan provides a very readable catalogue. For example, we learn that all images on the retina are blurred, and that we only see sharply due to the brain's efforts at picture enhancement. Sometimes, however — like any silent collaborator — the brain becomes lazy. A nerve cell given a strong stimulus fires enthusiastically to begin with, but soon becomes fatigued. This is why driving at high speed on a motorway feels normal so quickly after the initial acceleration. There is usually a good reason for this: like any idler, the brain excuses its sloth as energy conservation. For similar reasons the visual field is not as richly detailed as it at first seems — large expanses of colour are filled in, saving the brain the trouble of representing every blade of grass in the meadow. This is one trait evolved on the primordial savannah that suits us better in the modern world, because though it means that we fail to spot the odd poisonous spider in the grass, the author helpfully points out that such oversight enables us to enjoy Hollywood movies without noticing their constant continuity errors. Thankfully, no such devices are needed to appreciate this book, which entertains as it informs. If it is true that visual perception is the latest arm of philosophy to break away and join the sciences, The Space Between Our Ears is the narrative such a momentous event deserves.
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