Dement and Kleitman (1957)
Seven adult MALES and two adults FEMALES.
pp's told to avoid alcohol and caffine and to report just before normal bedtime. pp's were woke throughout the night by a doorbell and asked to recall a dream if they had been dreaming.
1. People are more likely to report dreams if they are woken during periods of REM than NREM.
2. People can estimate the duration of dreaming to an extent.