Grey matters

It is partly by research on the sensory capabilities of other organisms that we realise just how visual humans are. We have abandoned many of the senses other species possess. We can't smell our way up a pheromone-laden path, detect magnetic fields or electrical potentials, our brains contain no compasses by which we can navigate vast distances. The masses of nerve cells required for these skills in other animals are in humans devoted to analyzing and interpreting the signals arriving in the brain from our eyes. Michael Morgan, a distinguished neuroscientist, has written a popular book describing what we now know about how vision works. The 'grail' of insight into the basis of our conscious experience hangs over any such endeavour. For Morgan, understanding how electricity becomes perception offers the key to understanding what is going on but he is aware of the tricky ground. " One of the most useful comments I have seen on theories of consciousness was on a T-shirt at a neuroscience conference. Under a picture of the brain, the legend read: 'I think the brain is the most important and complicated organ in the body. But Hey, who's telling me this!' " He also sets out early his worries about language and how it may distort our analyses of brain function. " For obvious reasons, we should be particularly suspicious of claims coming from the language centers of the brain, which have a virtual monopoly on communication in our verbose society. Maybe when the language nerve cells tell us they are responsible for consciousness they should be told to get out more, to a football match or to the ballet. " But it is talk about eyes that fires Morgan up. " The message from the evolution of the eye is that 'big is beautiful'. Unlike most organs, the eye does not increase in proportion to body size, because its optical performance depends on its absolute, not its relative size. The sparrow's eye is as large as its brain and all its other sense organs put together, " he writes. Even so, it is no match for the eyes of larger animals. " The ostrich has the record for land-living animals, with an eye 50 mm in diameter, which enables it to see a bump on the ground 2 m high at a distance of 24 km. Horses, zebras and other plain-dwelling animals are not …