Variation in pupil diameter by day and time of day

Abstract

Over 60 years of prior work has shown that an individual’s pupil diameter increases as the cognitive demands of a task increase. Recent work has also shown that resting pupil size is significantly correlated with an individual’s working memory capacity, suggesting that between subjects variation in pupil size is important. Given the importance of both within and between variations in pupil size, the present study sought to examine the reliability of pupil diameter measurements across multiple days. A longitudinal, within subjects design was used to study pupil diameter to determine if it is possible to find stable estimates of pupil diameter across several days and across time of day. This study collected pupil data using a low-cost Gazepoint GP3 HD desktop eye tracking system. Seven participants engaged in a resting luminance change task twice per day for a total of 10 days. The participants sat in a completely dark room for two minutes prior to the start of the experiment to allow their eyes to acclimate to the darkness. They then performed the resting luminance change task, as well as two other tasks omitted from analysis. This paper presents an analysis demonstrating that there are stable estimates of pupil diameter across days, as well as across time of day. These results suggest that pupil diameter is a reliable measure within individuals. The ability to reliably capture pupil diameter using low-cost eye trackers suggests that these new low cost systems may be incorporated into a broader range of cognitive research.