Discussion
corneal
The present study examined the effects of intermittent morning bright white light exposure on simple and complex attentional performance. Potential light effects were quantified at the performance, subjective and physiological levels.Subjects showed improved attentional performance (i.e., they responded faster) under the brighter light pulse and higher corneal illuminance. Consistent with other studies (see, e.g.,Importantly, a short-lived faster reaction speed in the simple attention task was observed under the brighter light pulse without habituation (i.e., within each test cycle). However, this effect disappeared in the subsequent period of constant bright light exposure. These results suggest a complex interaction between changing light intensities and simple attentional performance.In contrast, we observed faster reaction speed in the complex attention task with constant bright light exposure, suggesting that a more demanding attention task involving not only sustained detection but also selection of relevant stimuli might benefit from constant exposure to bright light.Finally, error rates in both attentional tasks varied across the study day under both light interventions. Specifically, we observed more lapses in the aPVT in test cycle 4 and more commission errors in the GNT in test cycle 5. In contrast to other studiesNeuroimaging studies have shown that bright light exposure acutely alters autonomic nervous system activity by projecting photic information from ipRGCs and suprachiasmatic nuclei to the paraventricular nucleus of the hypothalamus and the locus coeruleus of the brainstemAdditionally, repetition of the attentional tests affected HRV independently of the light intervention, i.e., HRV was highest in the second test cycle. Moreover, HRV was comparable at the beginning and end of the study days. These results suggest an early physiological adaptation process at the beginning of each study day. They also suggest that repetition of attentional tasks may have increased physiological workload. However, our results do not clearly confirm diurnal physiological effects as reported elsewhereSubjective sleepiness-alertness ratings were not altered by bright light exposure in our study, which is in contrast to the results of systematic reviews (see, e.g.,Subjective ratings of workload at the end of each test cycle decreased slightly on each study day under both study conditions. Moreover, affective states were not altered by bright light exposure. These results give rise to the assumption that improved attentional performance was not moderated by altered perceived workload and affective states.Consistent with other studies in which the luminance levels in the field of view of study participants were carefully selected, e.g.,