Dehaene (Experimental Cognitive Psychology/Collège de France; Reading in the Brain: The Science and Evolution of a Human Invention, 2009) delivers a detailed popular account of what he and fellow researchers have discovered about how perceptions become thoughts.
Scientists once agreed with laymen that consciousness was a mystical phenomenon beyond the reach of experiments. Though many laymen still believe in that idea, scientists changed their minds more than 30 years ago. We pay attention to one thing at a time. Life would be impossible if the brain didn’t suppress almost everything our senses detect. This makes “eyewitness” testimony unreliable, and the Internet teems with clips of experimental subjects blithely ignoring the obvious. LSD users describe deeply profound perceptions, but they are simply overwhelmed with information since the drug turns off the brain’s suppressive function, making everything equally important. The unconscious is not merely a Freudian conjecture. Its operations are visible on brain imaging procedures and amenable to experiments. Furthermore, humans overestimate the power of consciousness. We routinely select a fraction of our unconscious pictures, amplify, name, memorize them, and use them to plan our actions. Consciousness research is turning up useful information. Catastrophic brain damage often reduces victims to vegetative or locked-in states during which they sleep and wake but remain unresponsive. New tests reveal a few whose brains (but not their bodies) respond to questions as if they were conscious. Barely conscious patients with relatively intact cerebral cortexes occasionally improve dramatically during electrical stimulation of the thalamus, a deep brain structure that regulates vigilance. “What is certain,” writes the author, “is that, in the next decades, the renewed interest in coma and vegetative states…will lead to massive improvements in medical care.”
A revealing and definitely not dumbed-down overview of what we know about consciousness.