The effects of two alternative timings of a one-hour nap on early morning performance

The effect on performance and sleepiness of two alternative timings of a one-hour nap (2100h and 0430h, respectively) were compared with a control condition (no nap). Twelve healthy male subjects divided into three groups participated in a partly balanced repeated measurements design. At all three occasions the subjects slept 4 h during the preceding night, worked during the day and were then kept awake (except for naps) in the laboratory from 1700h to 0800h the following morning. Performance was measured through a 10-min single choice visual reaction time task administered at 1900h and 0700h. Sleepiness was measured through self-ratings and sleep latency tests at 2100h and 0600h. The results showed clear positive effects of naps (especially the 0430h nap) on performance. The sleep latency measurements showed similar, but less clear tendencies, while ratings of sleepiness did not differentiate between conditions. It was concluded that a one-hour nap could counteract the late night performance decrement.