The Salience of Fire Alarm Signals for Sleeping Individuals: A Novel Approach to Signal Design\ud \ud

Contrary to popular belief, the human brain remains in a very active state during sleep, and being asleep is by no means equal to an absence of conscious experience. Previous research has shown that participants can produce a behavioural response to auditory stimuli during sleep without necessarily awakening. Such responses are elicited more readily during the subjectively lighter stages of sleep compared to the subjectively deeper stages. This is illustrated when we consider that auditory arousal thresholds (AAT’s) normally progressively decline across the night, which is commensurate with the declining proportion of time spent in deep sleep as sleep progresses