The relationship between subjective and objective sleepiness and performance during a simulated night-shift with a nap countermeasure

The aim of the present study was to investigate the relationship between perceived and actual sleepinessand performance during a simulated night-shift that included a 30-min night-nap as an on-dutysleepiness countermeasure. Twenty-four healthy young adults (nine males, fifteen females) participatedin a repeated measures design comprising two experimental conditions: no night-nap and 30-min nightnap.Both groups were given a 2-h prophylactic afternoon sleep opportunity (1500e1700 h). Measures ofsubjective sleepiness (Stanford Sleepiness Scale, Karolinska Sleepiness Scale and Visual Analogue Scale),objective sleepiness (sleep latency tests), objective performance (SymboleDigit Substitution Task) andreaction time (Psychomotor Vigilance Task) were taken before the night-nap (0230 h) and at severalintervals post-nap. Timeeseries correlation analyses indicated that subjective sleepiness was lesscorrelated with objective sleepiness and objective performance when participants were given a 30-minnight-nap. However subjective sleepiness and reaction time performance was strongly correlated in bothconditions, and there was no significant difference between the nap and no-nap conditions. Consistentwith previous research, results of the present study indicate that subjective and objective indicators ofsleepiness and performance may not always correspond, and this relationship may be reduced by theinclusion of a night-nap.