Naps significantly affected RTs in the lapse domain, however. The results of MannWhitney U tests at each trial test bout between the control group and respective treatment groups revealed that naps generally improved performance or prevented it from deteriorating as dramatically as it did with no nap opportunity. Of 35 comparisons made between treatment groups and the control group for trials after the naps, 23 (66%) produced significant differences. Of 25 comparisons made between groups for trials prior to the naps, 1 (4%) yielded significant results. Nap groups virtually never differed from the control group until after a nap was taken.
Although the positive effects of the P6 nap on RT lapses were not evident until 12 h after that nap (approximately 0500 h), when the P54 group had been awake for >20 h, these effects remained evident for most of the subsequent 30 h of the sleep loss trial (Fig. 1, upper left quadrant). This same result was found for the T18 nap, except that the differences appeared immediately after that nap (approximately 0500 h) and were even more robust (Fig. 1, upper right quadrant). The P30 nap also yielded significantly improved performance,