Time of day modulates our cognitive functions, especially those related to executive control, such as the ability to inhibit inappropriate responses. However, the impact of individual differences in time of day preferences (i.e. morning vs. evening chronotype) had not been considered by most studies. It was also unclear whether the vigilance decrement (impaired performance with time on task) depends on both time of day and chronotype. In this study, morning-type and evening-type participants performed a task measuring vigilance and response inhibition (the Sustained Attention to Response Task, SART) in morning and evening sessions. The results showed that the vigilance decrement in inhibitory performance was accentuated at non-optimal as compared to optimal times of day. In the morning-type group, inhibition performance decreased linearly with time on task only in the evening session, whereas in the morning session it remained more accurate and stable over time. In contrast, inhibition performance in the evening-type group showed a linear vigilance decrement in the morning session, whereas in the evening session the vigilance decrement was attenuated, following a quadratic trend. Our findings imply that the negative effects of time on task in executive control can be prevented by scheduling cognitive tasks at the optimal time of day according to specific circadian profiles of individuals. Therefore, time of day and chronotype influences should be considered in research and clinical studies as well as real-word situations demanding executive control for response inhibition.

Neurophysiological markers of the ability to sustain attention and exert inhibitory control of inappropriate responses have usually relied on neuroimaging methods, which are not easily applicable to real-world settings. The current research tested the ability of electroencephalographic and skin temperature markers to predict performance during the Sustained Attention to Response Task (SART), which demands vigilance and inhibitory control. In Experiment 1, we recorded the electroencephalogram (EEG) during the performance of SART and found that event-related potentials underlying inhibitory control (N1 and N2/P3) were influenced by a time on task effect, suggesting a decrement in attentional resources necessary for optimal inhibitory control. In Experiments 2 and 3, we recorded skin temperatures (distal, proximal and the distal-proximal temperature gradient -DPG) and found that they were sensitive to differential demands of mental workload, and that they were related to behavioural performance in the SART. This study suggests that the recording of EEG and skin temperature may be used to monitor fluctuations of attention in natural settings, although further research should clarify the exact psychological interpretation of these physiological indices.

The present study addressed the interactions between processes of circadian and millisecond timing by testing whether the ability for temporal preparation is influenced both by individual differences in circadian rhythmicity and by the time of day at which a task is performed. A temporal preparation task that measures temporal orienting and sequential effects was administered to morning-type and evening-type groups of participants, both in morning and evening sessions. The results confirmed a synchrony effect on overall reaction time (RT), indicating that participants were most vigilant at their optimal time of day according to their specific chronotype. This synchrony effect, however, did not influence temporal orienting or sequential effects. These findings suggest that only processes mediating overall RT (vigilance) but not processes related to temporal preparation are susceptible to circadian influence. The current research thus supports the dissociation between circadian timing and temporal preparation.

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