In fact, research suggests that only about 20 percent of dreams contain people or places that the dreamer has encountered. Most images appear to be unique to a single dream.
Scientists know this because some people have the ability to watch their own dreams as observers, without waking up. This state of consciousness, called lucid dreaming, is itself something a mystery — and a staple of New Age and ancient mystics. But it is a real phenomenon, one in which Dr. Hobson finds strong support for his argument for dreams as a physiological warm-up before waking.
In dozens of studies, researchers have brought people into the laboratory and trained them to dream lucidly. They do this with a variety of techniques, including auto-suggestion as head meets pillow (“I will be aware when I dream; I will observe”) and teaching telltale signs of dreaming (the light switches don’t work; levitation is possible; it is often impossible to scream).
Lucid dreaming occurs during a mixed state of consciousness, sleep researchers say — a heavy dose of REM with a sprinkling of waking awareness. “This is just one kind of mixed state, but there are whole variety of them,” Dr. Mahowald said. Sleepwalking and night terrors, he said, represent mixtures of muscle activation and non-REM sleep. Attacks of narcolepsy reflect an infringement of REM on normal daytime alertness.