Increasing pupil size is associated with improved detection performance in the periphery

Abstract

Visible light enters our body via the pupil. By changing its size, the pupil shapes visual input. Small apertures increase the resolution of high spatial frequencies, thus allowing discrimination of fine details. Large apertures, in contrast, provide a better signal-to-noise ratio, because more light can enter the eye. This should lead to better detection performance of peripheral stimuli. Experiment 1 shows that the effect can reliably be demonstrated even in a less controlled online setting. In Experiment 2, pupil size was measured in a laboratory using an eye tracker. The findings replicate findings showing that large pupils provide an advantage for peripheral detection of faint stimuli. 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. This suggests that in addition to absolute pupil size, the extent of pupillary change provides a mechanism to modulate perceptual functions. The results are discussed in terms of low-level sensory as well as higher-level arousal-driven changes in stimulus processing.

Keywords: Detection performance; Peripheral vision; Pupil size; Pupillometry.

Fig. 1

(A) Sequence of a trial with bright background brightness and stimulus position at 45°. (B) Sequence of a trial with dark background brightness and stimulus position at 45°. For each trial background brightness, stimulus position, and stimulus intensity were chosen in random order. After the start of a trial there was an inter-stimulus interval of 1–2 s. Subsequently the stimulus was faded in and out linearly for 0.651 s. The trial ended 2.2 s after stimulus onset

Fig. 2

Mean detection rates and standard errors as a function of stimulus intensity and background brightness in Experiment 1

Fig. 3

(A) Pupil size changes over time averaged across trials as a function of pupil size in the current trial n and the previous trial n-1, categorized by an average split. The gray area highlights the interval of 650 ms during which the stimulus was faded in and out. (B) Detection performance in trials with large pupil size as a function of stimulus intensity and pupil size in the previous trial. (C) Mean detection performance and in trials with small pupil size as a function of stimulus intensity and pupil size in the previous trial

Fig. 4

Fitted logistic mixed regression models plotted separately for the four stimulus intensities. The blue lines depict the effect of pupil size during information intake on the probability of detecting the stimulus (given a mean pupil size preceding information intake). The light gray and black lines plot the direction of the interaction between pupil size during and pupil size preceding information intake for preceding pupil sizes of 1 SD smaller (light gray) or larger (dark gray) than the mean pupil size