Diurnal variation in subjective states and cognitive performance: Empirical evidence from laboratory and real-world work settings.

This study systematically examined temporal dynamics in subjective states and cognitive performance using time‑of‑day protocols in both laboratory and real work settings. Twenty-four participants completed the field study and twenty‑one participants completed the laboratory study, with their self-reported sleepiness, vitality and mood being assessed at seven time points (08:30 h, 09:30 h, 11:00 h, 13:40 h, 14:30 h, 16:00 h, 17:30 h) and performance on sustained attention, executive inhibition and working memory being measured at six time points (08:30 h, 09:30 h, 11:00 h, 14:30 h, 16:00 h, 17:30 h). Results showed a significant time-of-day effect in subjective sleepiness and vitality, with a notable post-lunch decline (13:40 h-14:30 h) being more pronounced in real work environment. Subjective mood rendered more pronounced diurnal variations in natural settings, with positive mood being significantly lower at 16:00 h compared to 08:30 h and 09:30 h. Regarding cognitive performance, sustained attention showed optimal performance in the morning, whereas better working memory was observed in the afternoon, and executive inhibition showed minimal diurnal variation. Overall, cognitive performance exhibited greater variability in the real work environment than in the laboratory. The differences in finding between the laboratory and real work setting and the practical recommendations for optimizing subjective well-being and work efficiency in workplace have been discussed.