From the moment we wake we are bombarded with stimuli. Electromagnetic radiation floods our eyes, pressure waves hit our ears, surfaces press against our skins, molecules adhere to the membranes of our noses and tongues. Our sense organs react, sending nerve impulses to our brains, where they trigger waves of neural activity, which may culminate in motor commands to our muscles (shielding our eyes from the light, for example). But something else happens, too. We have conscious experiences. We see a bright light, hear a scream, feel the roughness of a surface. There is something it is like to detect the stimuli; each experience has a distinctive qualitative aspect - a quale in philosopher's jargon (plural qualia). Such experiences constitute what we call consciousness. But what is consciousness for? What do qualia do?

This may seem an odd question. The answer, surely, is that qualia carry information about the world. A red visual sensation tells us there is something red present; an acrid smell tells us something is burning; a pain tells us our body is damaged. There's a problem, however. For we could get this information without qualia. Engineers build robots with computer vision systems that can detect and classify colours, shapes, and movements with considerable accuracy. They don't need to give the robots qualia. Indeed, sometimes we behave in a robotic way ourselves. Most drivers have had the experience of driving absentmindedly, without paying attention to the road. Yet during these spells we must still be taking in visual information or we would crash. Or consider blindsight, a condition discovered in the 1970s by the psychologist Nicholas Humphrey. Humphrey studied a macaque monkey, Helen, whose primary visual cortex had been surgically removed. By the usual tests Helen was blind, but Humphrey discovered that, with encouragement, she could detect a range of visual stimuli, and in time she was able to interact with her surroundings almost as if fully sighted. ( See a video of Helen and read Humphrey's report.) Blindsight has been discovered in humans too, and the patients confirm that, though they can accurately 'guess' shapes and colours, they have no conscious visual sensations.

It appears, then, that the brain can do the work of perception without qualia. So, again, what is consciousness for? In his 2011 book Soul Dust, Humphrey proposes a novel idea. He argues that consciousness enriches life. It doesn't add information; it adds interests and goals. Qualia are wonderful, magical things, and conscious creatures enjoy having them. They relish their sensations, and this relish gives them a deeper interest in their own existence. They also project qualia onto their surroundings and take a deeper interest in them too; and they come to think of themselves as having a self, which is of great importance to them. These developments, Humphrey argues, have great survival value and explain why evolution equipped us with consciousness. ( Watch Humphrey talking about these ideas.) ...[Continue reading on Aeon Ideas]