Arousal-based pupil modulation is dictated by luminance

Abstract

Pupillometry has become a standard measure for assessing arousal state. However, environmental factors such as luminance, a primary dictator of pupillary responses, often vary across studies. To what degree does luminance interact with arousal-driven pupillary changes? Here, we parametrically assessed luminance-driven pupillary responses across a wide-range of luminances, while concurrently manipulating cognitive arousal using auditory math problems of varying difficulty. At the group-level, our results revealed that the modulatory effect of cognitive arousal on pupil size interacts multiplicatively with luminance, with the largest effects occurring at low and mid-luminances. However, at the level of individuals, there were qualitatively distinct individual differences in the modulatory effect of cognitive arousal on luminance-driven pupillary responses. Our findings suggest that pupillometry as a measure for assessing arousal requires more careful consideration: there are ranges of luminance levels that are more ideal in observing pupillary differences between arousal conditions than others.

Methods in Cognitive Pupillometry: Design, Preprocessing, and Statistical Analysis

“…Pupil size varies between roughly 2 and 8 mm in diameter (Mathôt, 2018; Pan et al, 2022). For most cognitive-pupillometry experiments, baseline pupil size should not approach these extremes, for the simple reason that maximally constricted or dilated pupils cannot constrict or dilate any further in response to experimental manipulations.…”

“…However, within a broad range of baseline pupil sizes, and thus for a broad range of ambient light levels, task-evoked pupil responses are reliably observed (Bradshaw, 1969; Cherng et al, 2020; Pan et al, 2022; Peysakhovich et al, 2017; Reilly et al, 2019; Steinhauer et al, 2004). As a rule of thumb, baseline pupil sizes between 3 and 7 mm are suitable.…”

“…Experiments should therefore not be conducted in a very dark or very bright environment (unless there are specific reasons to do so, for example if the experiment requires dark-adapted pupils). However, within a broad range of baseline pupil sizes, and thus for a broad range of illuminance levels, task-evoked pupil responses are reliably observed (Bradshaw, 1969; Cherng et al, 2020; Pan et al, 2022; Peysakhovich et al, 2017; Reilly et al, 2019; Steinhauer et al, 2004). As a rule of thumb, baseline pupil sizes between 3 and 7 mm are suitable.…”

Age-specific influences of refractive error and illuminance on pupil diameter

“…The results of the mixed model are reported in the form of effect estimates and its confidence interval in Table 3. [18,22] For this analysis, pupil diameter was considered a dependent variable. Independent factors were age groups (20-39 years; 40-49 years; 50-59 years; and 60-69 years), illuminance condition (scotopic: 0.0 lx; mesopic low: 0.3 lx; mesopic high: 3 lx), refractive error (best sphere: myopes, ≤-0.5 D; emmetropes, ≥-0.25 to ≤+0.50 D; and hyperopes, ≥+0.75 D), and sex.…”

“…[17] It has been found that "effect of cognitive arousal on pupil size interacts multiplicatively with luminance, with the largest effects occurring at low and medium luminance." [18]…”