Improving pupil diameter measurement accuracy in a remote eye tracking system

Abstract

Pupil diameter (PD) has been used to track changes in mental effort across a broad range of cognitive tasks for over 60 years. PD is often measured from remote eye tracking systems, which all have the same limitation: the lack of a known reference value to convert the pixels captured within the systems to millimeters. Researchers frequently normalize their data within an individual to overcome this issue, however recent studies have found individual differences in resting PDs. This paper investigated the use of a fiduciary marker of a fixed size and an individual’s interpupillary distance, as known reference values. Both techniques substantially improved the accuracy of PD data compared to the unadjusted system data. Further, the average difference between both techniques and the uncorrected pupil diameter was just under.4mm, which is approximately the equivalent of most studies finding differences in cognitive load.