The effects of asking for verbal ratings of sleepiness on sleepiness and its masking effects on performance

Objective This study investigated whether verbal rating sleepiness will itself affect sleepiness and performance. Methods Thirteen healthy male volunteers (mean age, 26.9 years) performed two 40-min vigilance tests, one of which involved verbal ratings every 4 min using the Karolinska sleepiness scale and another of which did not involve any ratings during the test. Results Repeated rating of sleepiness significantly reduced post-test sleepiness and improved the subjective perception of performance, and also reduced alpha power density (i.e., a physiological indicator of sleepiness). However, performance was not improved by the ratings. Conclusions The act of rating affects subjective and EEG measures of sleepiness. Presumably this occurs through the modest stimulation involved in this act. Significance Methodologically one should be aware of subtle effects of the rating situation on sleepiness. From a practical point of view, it would be important for safety management since subjective sleepiness and performance are easily dissociated, which might interfere with risk perception.