Publication guidelines and recommendations for pupillary measurement in psychophysiological studies

Abstract

A variety of psychological and physical phenomena elicit variations in the diameter of pupil of the eye. Changes in pupil size are mediated by the relative activation of the sphincter pupillae muscle (decrease pupil diameter) and the dilator pupillae muscle (increase pupil diameter), innervated by the parasympathetic and sympathetic branches, respectively, of the autonomic nervous system. The current guidelines are intended to inform and guide psychophysiological research involving pupil measurement by (1) summarizing important aspects concerning the physiology of the pupil, (2) providing methodological and data-analytic guidelines and recommendations, and (3) briefly reviewing psychological phenomena that modulate pupillary reactivity. Because of the increased ease and tractability of pupil measurement, the goal of these guidelines is to promote accurate recording, analysis, and reporting of pupillary data in psychophysiological research.

Keywords: dilation; parasympathetic; pupil constriction; pupillography; pupillometry; sympathetic.

FIGURE 1

(a) Image of the eye. (b) Area of concentric sphincter muscles outlined in red, radial dilator muscles shown in blue

FIGURE 2

Schematic of the pupillary light reflex pathway (adapted from Kelbsch et al., 2019)

FIGURE 3

Sympathetic (magenta/red) and parasympathetic pathways (green) (adapted from Wilhelm, 2011)

FIGURE 4

Pupillary dilation during digit span task (7 and 10 digits) under light and dark recording conditions. First digit was presented at 2 s. Increased dilation amplitude is observed for the pupil when recorded in light (blue) vs. darkness (green). Highlighting under the x-axis represents sample-wise significance, where yellow = p < .1 and red = p < .05. Underlined highlighted periods were long enough to infer significance using Guthrie and Buchwald’s (1991) Type I error correction technique (see Section 2.3.4)

FIGURE 5

(a) Average pupillary waveforms when listening to novel emotional or neutral sounds in an auditory oddball task, recorded under conditions of light and darkness. (b) Two major principal components depicting factor loadings over time (adapted from Widmann et al., 2018)

FIGURE 6

Video output using count of vertical scan lines. When measuring vertical pupil diameter, the center white spot is a reflection from an infrared light source, which is also measured when evaluating eye location for eye tracking

FIGURE 7

Zoomed segment of preprocessed pupillary data showing raw pupil horizontal diameter (blue), effect of smoothing and interpolation through blinks (red), and serial port markers showing trial onsets/events (yellow) (courtesy G. Siegle)

FIGURE 8

Parallax effect of lateral gaze. (a) The eye looking forward is circular. (b) The eye is rotated to the right, distorting the measurable horizontal diameter

FIGURE 9

Pupil diameter waveforms when viewing bright, moderate, or dark stimuli illustrate changes in the amplitude of the light reflex (courtesy M. Bradley)

FIGURE 10

(a) For full-field stimuli that are equivalent in pixel intensity but different in pixel contrast, light reflex amplitude is greater for scenes that are high in contrast (brighter whites). (b) For stimuli that are equivalent in pixel intensity and contrast, light reflex amplitude is greater for scenes in which the foreground stimulus is brighter (courtesy M. Bradley)

FIGURE 11

(a) Pupil diameter is linearly related to the pixel intensity (luminance) at fixation for scenes that are equivalent in pixel intensity and contrast (luminance) when full-field scenes are presented (inset) and eye movements allowed. (b) Pupil diameter is no longer linearly related to pixel intensity at fixation when scenes are presented in a matrix (5 × 5; inset) so that each fixation includes all luminance variations. In both (a) and (b) of Figure 11, each point is one scene and all scenes were pre-experimentally manipulated so that mean pixel intensity was 140 (8-bit grayscale stimulus) (courtesy M. Bradley)

FIGURE 12

Pupil diameter and the light reflex (change from baseline) as a function of baseline and experimental stimulation (5 × 5 matrix of pictures). (a) A constant baseline stimulus is equivalent in luminance to the experimental stimuli. (b) A variable baseline stimulus is equivalent in luminance to the experimental stimuli. (c) A constant baseline stimulus is different in luminance from experimental stimuli that vary across the study. (d) A variable baseline stimulus is different in luminance from experimental stimuli that vary across a study. The brighter the legend or lines, the brighter the baseline and/or experimental stimulus (courtesy M. Bradley)

FIGURE 13

PIPR: Pupil light reflex (PLR) in response to 639 nm (red) and 463 nm (blue) narrow bandwidth stimuli of 200 ms duration, 14.5 log photons/cm²/s. The most commonly reported PIPR measure (4; AUC late; Adhikari et al., 2015) is indicated in yellow, along with other important PIPR metrics. Data reflect a single response to red and blue stimuli from a healthy control participant (courtesy K. Roecklein, P. Gamlin, P. Franzen, G. Siegle)

FIGURE 14

Increasing pupil dilation as event probability decreases for: (a) counting of rare tones (0.33 probability), and (b) RT to different tones (Steinhauer & Hakerem, 1992)