Mental mappers work in a world turned upside down

Breathing takes place in the lungs and digestion in the stomach, but vision does not happen in the eye; it is our brain that interprets the constantly changing patch of light landing on our retina. The man in the moon, the shapes we see in the clouds: the brain is churning away, extracting patterns, inferring - sometimes wrongly - the nature of our environment.

When we hallucinate or dream, activity takes place in the brain. Where is the link between the world of sensations and the electrical signals of the brain? As we speak, scientists are trying to dissect the brain to find where consciousness might reside.

Michael Morgan's The Space between Our Ears , the latest in a spate of books on visual consciousness, addresses this subject by asking, "How does our brain represent visual space?" In other words, how can the activity of some neurons mean "here" and others mean "there"? On the way, he answers other easier questions, such as "Why do I feel sick when reading in a car?"

The book, which is aimed at a general audience, draws in the reader with diverting anecdotes that make it a relatively easy read. At the same time, Morgan subtly leads the reader through a quick overview of knowledge. For the expert, the book is a refreshing break from the textbook format and bang up to date.

The central theme is the importance of maps. It cannot be a coincidence, the book argues, that cells that respond to neighbouring visual stimuli with similar attributes are also located close together in the brain. It looks as if we have many cortical maps of the world. Every map needs a key - could the key to visual maps yield a clue to the nature of consciousness?

In this book, we learn about the many mechanisms in the brain that have evolved to use all the tricks available to decode colour, depth, motion and other aspects of the scene. Although much use is made of the idea of the brain as many computing modules, Morgan also warns of the danger of imagining the brain as a modern digital PC.

A great deal of visual research relies on measuring how single neurons respond to light. More recent techniques scan the blood flow to active areas of the brain. The author points out the misleading conclusions that can be drawn from either technique.

Illustrated examples and analogies drawn from life and history help the reader understand the computational difficulties involved in using visual input to navigate a complex world. Throughout, the book stresses the importance of experimentation and encourages readers to take part. A section at the end lists simple experiments one can perform on oneself.

There is no need for a telescope or a microscope; we all have a whole unexplained universe of perceptions to explore.

In the final part, the question of how decoded and remapped information adds up to visual sensation needs to be addressed. The debate is presented through the available empirical evidence without getting lost in philosophy. While Morgan is fairly scathing on the search for the seat of consciousness, he shies away from a theory of his own. He does suggest, however, that a computer could never be conscious, though his reasoning still leaves this question open.

It is clear why this book, winner of the Wellcome Trust Prize for popular science writing, has been well received. It is accessible without being patronising. It weaves together centuries-old discoveries with current controversies, all the while highlighting the importance of clear-headed scientific inquiry that anyone can initiate. The book grabs the novice and rekindles the enthusiasm of the vision scientist, even if one occasionally disagrees with the opinions it expresses.

In this age of fear and mistrust of scientists, this book is timely, pointing out that scientists are only people. Indeed, anyone can be a scientist, as long as he is prepared to appear faintly ridiculous looking "at the world through a mirror with his head upside down".

Szonya Durant is fellow in psychology, University of Sydney, Australia.