Auditory thresholds during continuing sleep

Five subjects were asked to respond to a 1000 Hz tone with a standard button push response during sleep. A method of limits procedure was used to track their auditory thresholds when awake and during various stages of sleep. Subjects adapted to the procedure and were able to make consistent responses while their EEG indicated stage 1 or stage 2 sleep. While the threshold level at which a response was made was directly related to EEG state, there was no significant correlation between the interval between responses and the threshold level. It was concluded that stable auditory thresholds could be obtained during stage 1 and stage 2 sleep after little laboratory adaptation and that this behavioral response could be a useful indicator of central processing ability during sleep.