Fig. 8: Humans perceive luminance transient coinciding with pupil constriction.

A Setup of human psychophysics experiment. Top: Human subjects (4 male and 4 female) were presented full-field stimulus on computer screen and asked to report perceived change in luminance during a 3-s flash. Middle: Stimulus, a full-field-flash of high contrast (corresponding to LL5 stimulus presented in mice) or low contrast (corresponding to LL1 stimulus presented in mice). Bottom: Prediction of perceptual dimming. We hypothesized that subjects would perceive dimming of the stimulus in time with PLR due to decreased luminance on the retina (red arrow). B Examples of 2 subjects reporting perceptual dimming during low-contrast (orange) and high-contrast (green) stimulus. Change in pupil size during stimulus presentation (dark gray: mean, light gray: individual trials). Dots: Time of reported dimming. X: trials with no detected dimming. Throughout figure, orange indicates low contrast stimulus, green high contrast. C Perceptual dimming in all volunteers. Top: Dimming detection during low-contrast stimulation. Time of dimming detection for each of the subjects (colored dots) and number of trials with no detection (black X). The plot is the change in pupil size (line: mean, shaded area ± SEM). Bottom; Same as top, but for high-contrast stimulation. Blue line = 1 s. D Detection times shown in C (bottom histograms) aligned to pupil response (top traces). E Percentage of trials where dimming was detected during low contrast (orange) compared to high contrast (green) stimulation, n = 8, p = 0.013 (*), paired two-sided t-test. Black dot is mean across volunteers, bars indicate ± SEM. F Difference between each dimming detection and PLR peak time during low-contrast stimulation for all the subjects. PLR start and end (dotted line) are approximated from mean PLR shown in (C). (n = 40 detection events, N = 6 humans).