Conscious experience is at once the most familiar thing in the world and the most mysterious. There is nothing we know about more directly than consciousness, but it is extraordinarily hard to reconcile it with everything else we know. Why does it exist? What does it do? How could it possibly arise from neural processes in the brain? These questions are among the most intriguing in all of science.

From an objective viewpoint, the brain is relatively comprehensible. When you look at this page, there is a whir of processing: photons strike your retina, electrical signals are passed up your optic nerve and between different areas of your brain, and eventually you might respond with a smile, a perplexed frown or a remark. But there is also a subjective aspect. When you look at the page, you are conscious of it, directly experiencing the images and words as part of your private, mental life. You have vivid impressions of colored flowers and vibrant sky. At the same time, you may be feeling some emotions and forming some thoughts. Together such experiences make up consciousness: the subjective, inner life of the mind.

For many years, consciousness was shunned by researchers studying the brain and the mind. The prevailing view was that science, which depends on objectivity, could not accommodate something as subjective as consciousness. The behaviorist movement in psychology, dominant earlier in this century concentrated on external behavior and disallowed any talk of internal mental processes. Later, the rise of cognitive science focused attention on processes inside the head. Still, consciousness remained off-limits, fit only for late-night discussion over drinks.

Over the past several years, however, an increasing number of neuroscientists, psychologists and philosophers have been rejecting the idea that consciousness cannot be studied and are attempting to delve into its secrets. As might be expected of a field so new, there is a tangle of diverse and conflicting theories, often using basic concepts in incompatible ways. To help unsnarl the tangle, philosophical reasoning is vital.


Cosmica Naturata