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Aim: To assess circadian fluctuations in healthy subjects in single attentional components (selective/divided) and switching between them, using the new AD-Task instrument. Materials: 18 participants (16 F) completed the AD-Task at different times of the day and were monitored on indices of sleep quality and sleepiness level. Method: The entire experimental protocol was conducted over two days: on day 1 participants performed a brief familiarization phase with the AD-Task; on day 2 they assessed their sleepiness level and then performed the full version of the AD-Task at different times. Task execution took about 50 minutes, and performance was evaluated by considering both reaction time (RT) and accuracy indices (Hit Rate; d'). Results: All participants reported good sleep quality and stable subjective sleepiness indices. A repeated-measures ANOVA with the within-subject factors “TIME”, “CONDITION ‘and ’ATTENTIONAL DEMAND TYPE” showed an interaction effect between TIME and ATTENTIONAL DEMAND TYPE factors on all variables considered (RT= F (3,51) =13.958, p<.001; HIT RATE= F (3,51) =5.362, p=.003; d' = F (3,51) =14.332; p<.001). Post-hoc analyses revealed better performance for both RT and accuracy in selective attention than in divided attention. In addition, a good sensitivity to circadian fluctuations was more evident in divided attention, which showed greater difficulty in achieving optimal performance in the early morning and post-lunch phase, than in selective attention, which maintained a more stable and optimal performance, peaking in the late morning. Conclusions: In the circadian context, attentional components behave differently, and the AD-Task effectively measures both selective and divided attention.
