Effects of age on auditory awakening thresholds.

Auditory awakening thresholds ( AATs ) were assessed in sleeping men and women at three age levels (18 to 25, 40 to 48, and 52 to 71 years) with a procedure that employed a 5-sec tone in accordance with the up-and-down method. Although age was less influential than individual differences in predicting AAT levels, there was a significant and substantial AAT decline from early adulthood to later life in Sleep Stages 4, 2, and REM. With no variation by sex, this progressive decline was apparent by the 40s in Stages 4 and 2 and was sharpest from one age level to another in Stage 4. Decline was more gradual and delayed in REM, probably because of a sampling artifact based on stimulus incorporation in dreams. These findings help to explain increased sleep disturbance in the later years as a result of diminished intensity of sleep, which makes sleep more difficult to sustain.