THE LOGIC OF SLEEP-LEARNING: Page 19

falling asleep, and which recurs about one hour before awakening. It is during this state, psychologists have found, that the subconscious is most receptive. Once reception has been definitely established, the student may start using the Transitional Sleep Period, which usually begins three hours and forty minutes after falling asleep. This is the transition between the third and fourth (the deepest) stage of sleep, and material received by the subconscious during this transitional period is remembered most rapidly of all. The explanation for this is not known. Specialists in sleep-learning are unable to state with certainty how long it will take to absorb a message in sleep-study. They do know that for most people the number of impressions (repetitions) necessary to memorize material during sleep is most certainly a great deal less than the number needed while awake. The experiments of Dr. Wilder Penfield of the Montreal Neurological Institute established that the natural tape recorders in our heads require only one impression for retention—possibly lifelong. Dr. Penfield discovered this during surgery on patients under local anaesthesia. He stimulated certain brain cells with gentle electric current and the patients, who were conscious, reported perfect playbacks of conversations, songs, and other experiences as far back as childhood. This is considered by sleep-learning researchers to be potentially meaningful in yielding explanations of reports that students awakened between two and five o'clock in the morning received an entirely different message from the one they had put on tape.