The effect of pupil size and peripheral brightness on detection and discrimination performance

Abstract

It is easier to read dark text on a bright background (positive polarity) than to read bright text on a dark background (negative polarity). This positive-polarity advantage is often linked to pupil size: A bright background induces small pupils, which in turn increases visual acuity. Here we report that pupil size, when manipulated through peripheral brightness, has qualitatively different effects on discrimination of fine stimuli in central vision and detection of faint stimuli in peripheral vision. Small pupils are associated with improved discrimination performance, consistent with the positive-polarity advantage, but only for very small stimuli that are at the threshold of visual acuity. In contrast, large pupils are associated with improved detection performance. These results are likely due to two pupil-size related factors: Small pupils increase visual acuity, which improves discrimination of fine stimuli; and large pupils increase light influx, which improves detection of faint stimuli. Light scatter is likely also a contributing factor: When a display is bright, light scatter creates a diffuse veil of retinal illumination that reduces perceived image contrast, thus impairing detection performance. We further found that pupil size was larger during the detection task than during the discrimination task, even though both tasks were equally difficult and similar in visual input; this suggests that the pupil may automatically assume an optimal size for the current task. Our results may explain why pupils dilate in response to arousal: This may reflect an increased emphasis on detection of unpredictable danger, which is crucially important in many situations that are characterized by high levels of arousal. Finally, we discuss the implications of our results for the ergonomics of display design.

Influence of Lenslet Configuration on Short-Term Visual Performance in Myopia Control Spectacle Lenses

“…Moreover the CS under photopic condition was higher than that in mesopic illumination. Higher light levels induce smaller pupils by increasing the depth of focus and minimize the effects of higher-order aberrations by reducing the size of the blurred circle on the retina ( Holladay et al, 1991 ), resulting in an increase of VA ( Lombardo and Lombardo, 2010 ) and improved discrimination of fine stimuli ( Xu et al, 2017 ; Mathôt and Ivanov, 2019 ).…”

Pupil Size Reflects Exploration and Exploitation in Visual Search (and It’s Like Object-Based Attention)

“…Specifically, small pupils provide high visual acuity (by reducing optical distortions of the lens), and thus facilitate PUPIL SIZE REFLECTS EXPLORATION AND EXPLOITATION BEHAVIOR 7 stimulus discrimination. In contrast, large pupils provide high visual sensitivity (by allowing more light to enter the eye) and thus facilitate stimulus detection, which is especially beneficial in darkness (e.g., see Mathôt & Ivanov, 2019;Woodhouse, 1975). A fully dilated pupil can constrict from about 8 mm to approximately 2 mm when exposed to intense brightness (Walker et al, 1990) and this sixteenfold decrease in pupil area has a substantial impact on vision.…”

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

“…Respective changes have frequently been attributed to differences in attentional processing (e.g., Brocher et al, 2018;Klatt et al, 2021;Unsworth & Robison, 2016;Van Kempen et al, 2019). However, a recent hypothesis suggests that the function of arousal-linked pupillary changes is to tune vision at the point of initial sensory intake to improve perception (Ebitz & Moore, 2019;Mathôt, 2020;Mathôt & Ivanov, 2019). This would imply that visual task performance is in some cases not only affected by central activation, but also by mere sensory information.…”