Assessing subjective sleepiness during a night of sleep deprivation: examining the internal state and behavioral dimensions of sleepiness.

Investigators in previous research have indicated that subjective measures of sleepiness may separate into state- and behavior-based dimensions; however, researchers have not examined this under sleep deprivation conditions. The authors' purpose in this study was to examine several measures of subjective sleepiness under sleep deprivation conditions following completion of various tasks. Fourteen students participated in a 28-hour sleep deprivation study and completed vigilance and cognitive tasks 4 times during the night. The authors administered subjective measures of sleepiness after each task. Factor analyses indicated that when individuals were not excessively sleepy, subjective sleepiness measures separated into 2 dimensions: state and behavioral sleepiness. However, when individuals were more fatigued, there was no distinction between the state and behavior dimensions of sleepiness. The current results suggest that using measures that assess state and behavioral sleepiness separately could be useful in clinical and research settings when extreme levels of sleepiness are not expected.