“Blue Sky Effect”: Contextual Influences on Pupil Size During Naturalistic Visual Search

Abstract

Pupil size is influenced by cognitive and non-cognitive factors. One of the strongest modulators of pupil size is scene luminance, which complicates studies of cognitive pupillometry in environments with complex patterns of visual stimulation. To help understand how dynamic visual scene statistics influence pupil size during an active visual search task in a visually rich 3D virtual environment (VE), we analyzed the correlation between pupil size and intensity changes of image pixels in the red, green, and blue (RGB) channels within a large window (~14 degrees) surrounding the gaze position over time. Overall, blue and green channels had a stronger influence on pupil size than the red channel. The correlation maps were not consistent with the hypothesis of a foveal bias for luminance, instead revealing a significant contextual effect, whereby pixels above the gaze point in the green/blue channels had a disproportionate impact on pupil size. We hypothesized this differential sensitivity of pupil responsiveness to blue light from above as a “blue sky effect,” and confirmed this finding with a follow-on experiment with a controlled laboratory task. Pupillary constrictions were significantly stronger when blue was presented above fixation (paired with luminance-matched gray on bottom) compared to below fixation. This effect was specific for the blue color channel and this stimulus orientation. These results highlight the differential sensitivity of pupillary responses to scene statistics in studies or applications that involve complex visual environments and suggest blue light as a predominant factor influencing pupil size.

Eye movements decrease during effortful speech listening

“…Pupillometry – the measurement of pupil dilation – is the most used objective tool to assess listening effort (Winn et al, 2018; Zekveld et al, 2018; Kadem et al, 2020). However, pupil dilation is sensitive to environmental changes in luminance (Knapen et al, 2016) and light spectrum (Suzuki et al, 2019; Thurman et al, 2021), and is therefore difficult to use outside of the laboratory. Moreover, measuring pupil dilation accurately requires participants to continuously fixate on a point on a computer monitor (Ohlenforst et al, 2017; Zekveld et al, 2018; Farahani et al, 2020; Winn and Teece, 2021), because luminance changes arising from eye movements change the pupil dilation and different angles of the pupil relative to the eye-tracker can make the pupil diameter appear different without an actual difference (Brisson et al, 2013; Hayes and Petrov, 2016; Fink et al, 2021).…”

The Eye Pupil Adjusts to Illusorily Expanding Holes

“…Similarly, we surmise that the distribution of gradients that are encountered ecologically when experiencing glare may strengthen the sensitivity for cyan, particularly compared with yellow. Moreover, the Helmholtz-Kohlrausch effect ( Corney et al, 2009 ) is stronger with blueish patches, and this effect could be in part behind the constrictive effect on the pupil of blue gradients ( Suzuki et al, 2019 ), especially when these are present in the upper visual field ( Thurman et al, 2021 ), also consistent with the natural ecology of sunlight.…”

Pupil size and eye movements differently index effort in both younger and older adults

“…Zekveld, Koelewijn, & Kramer, 2018). However, pupil size can vary due to factors unrelated to task demands, such as changes in light (Knapen et al, 2016; Suzuki, Minami, Laeng, & Nakauchi, 2019; Thurman et al, 2021) or in the angle of the eye relative to the eye-tracking camera (Brisson et al, 2013; Fink et al, 2023; Hayes & Petrov, 2016). To address the latter, individuals typically maintain fixation on a point on a computer monitor (Kraus, Obleser, & Herrmann, 2023; Matthew B.…”

“…B. Winn, Wendt, Koelewijn, & Kuchinsky, 2018;Adriana A. Zekveld, Koelewijn, & Kramer, 2018). However, pupil size can vary due to factors unrelated to task demands, such as changes in light (Knapen et al, 2016;Suzuki, Minami, Laeng, & Nakauchi, 2019;Thurman et al, 2021) or in the angle of the eye relative to the eye-tracking camera (Brisson et al, 2013;Fink et al, 2023;Hayes & Petrov, 2016). To address the latter, individuals typically maintain fixation on a point on a computer monitor Matthew B. Winn & Teece, 2021;Adriana A. Zekveld et al, 2018), but restriction of gaze can reduce memory and mental imagery (Johansson, Holsanova, Dewhurst, & Holmqvist, 2012).…”

“…Pupillometry – the measurement of the pupil size – is commonly used to assess effort (van der Wel and van Steenbergen, 2018; Winn et al, 2018; Zekveld et al, 2018). However, pupil size can vary due to factors unrelated to task demands, such as changes in light (Knapen et al, 2016; Suzuki et al, 2019; Thurman et al, 2021) or in the angle of the eye relative to the eye-tracking camera (Brisson et al, 2013; Hayes and Petrov, 2016; Fink et al, 2021). To address the latter, individuals typically maintain fixation on a point on a computer monitor (Zekveld et al, 2018; Winn and Teece, 2021; Kraus et al, 2023a), but restriction of gaze can reduce memory and mental imagery (Johansson et al, 2012).…”