Discrimination of early sleep stages: behavioral indicators

Six subjects participated in a one-night sleep-onset experiment. They were aroused from stage 1 and stage 2 as defined by standard electroencephalographic criteria. Subjects pressed a button upon arousal to indicate which of two subjective states they were in just before awakening. Performance accuracy from stage 1 awakenings appeared to remain relatively constant at approximately 83%; performance from stage 2 awakenings showed increasing accuracy. Response latencies increased between stage 1 and stage 2 awakenings.