More specifically, pupil size is demonstrated to reflect changes in activation in the locus-coeruleus (LC) and the associated noradrenergic system (Joshi et al., 2016 Murphy et al., 2014). Pupillary changes also co-occur with changes in arousal. Pupils adjust to provide the optimal visual image quality, when co-varying with brightness as well as with changes within the near-triad (e.g., Campbell, 1957 Campbell & Gregory, 1960 Charman & Whitefoot, 1977 Crawford, 1936 Feil et al., 2017 Woodhouse, 1975). The present paper presents two experiments addressing this question, using brightness-induced pupil size changes. This raises the question of which perceptual consequences arise from the covariation of pupil size with numerous causes. Thus, changes in pupil size result in changes in optics. Pupil size determines how much light enters the retina. As such, pupil sizes co-vary with a variety of cognitive processes, spanning such diverse phenomena as emotional activation, mental effort, or making simple decisions (see Einhäuser, 2017 and Mathot, 2018). Interestingly, pupil size changes not only accompany changes in illuminance and within the near-triad, but also fluctuations in central arousal. The light reflected by an object enters our body via an aperture in our eyes, the pupil. The results are discussed in terms of low-level sensory as well as higher-level arousal-driven changes in stimulus processing. This suggests that in addition to absolute pupil size, the extent of pupillary change provides a mechanism to modulate perceptual functions. Moreover, not only pupil size during information intake in the current trial n, but also its interaction with pupil size preceding information intake, i.e., in trial n-1, predicted performance. The findings replicate findings showing that large pupils provide an advantage for peripheral detection of faint stimuli. In Experiment 2, pupil size was measured in a laboratory using an eye tracker. Experiment 1 shows that the effect can reliably be demonstrated even in a less controlled online setting. This should lead to better detection performance of peripheral stimuli. Large apertures, in contrast, provide a better signal-to-noise ratio, because more light can enter the eye. ![]() Small apertures increase the resolution of high spatial frequencies, thus allowing discrimination of fine details. By changing its size, the pupil shapes visual input. Visible light enters our body via the pupil.
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