Stage at awakening, sleep inertia, and performance

Our purpose was to verify if the differential effect of final stage at awakening varies with the amount of sleep reduction and if this effect goes beyond the boundaries of sleep inertia. Seven university students were paid for their participation. The design included two conditions, REM (three consecutive nights) and NREM (three consecutive nights). Sleep length was progressively curtailed to 6 hrs, 4.5 hrs and 3 hrs for the first, second and third night, respectively. In the REM condition, participants were awakened during REM sleep, while in the NREM condition, participants were awakened during Stage 2. Days following experimental nights were devoted to the assessment of performance. Test sessions were scheduled upon awakening and then every three hours thereafter. Performance was measured by means of a Simple Reaction Time task and a Four Choice reaction time task. Results show that sleep inertia after NREM awakenings is more pronounced than after REM awakenings. Sleep curtailment enhances this differential effect and prolongs it beyond sleep inertia boundaries. Final stage at awakening not only exerts a differential influence on performance within the sleep inertia phase, but also impairs performance after NREM awakenings following inertia dissipation, especially when sleep is curtailed.