I suggested that dreams are simulations of the world created by our perceptual systems. The introduction to waking perception that you just read will help you understand this theory.

Consider, first of all, how sleep modifies the process of perception. During REM sleep, as you learned in chapter 2, sensory input from the outside world and body movement are both suppressed, while the entire brain is highly active. The activity of the brain raises certain schemas above their perceptual thresholds. These schemas enter consciousness, causing the dreamer to see, feel, hear, and experience things not present in the external environment.

Ordinarily, if you were to see something that wasn't really there, contradictory sensory input would rapidly correct your mistaken impression. Why doesn't the same thing happen during dreaming? The answer is because there is little or no sensory input available to the brain for correcting such mistakes.

But why are people interested in learning to be conscious in their dreams? According to my own experience, and the testimony of thousands of other lucid dreamers, lucid dreams can be extraordinarily  vivid, intense, pleasurable, and exhilarating. People frequently consider their lucid dreams as among the most wonderful experiences of their lives.

If this were all there were to it, lucid dreams would be delightful, but ultimately trivial entertainment. However, as many have already discovered, you can use lucid dreaming to improve the quality of your waking life. Thousands of people have written to me at Stanford telling how they are using the knowledge and experience they have acquired in lucid dreams  to help them get more out of living.