Additional Evidence for Pupil Size as a Measure of Within-Task Learning

Abstract

This study sought to improve and extend previously conducted research that demonstrated the ability to capture within-task learning by measuring changes in an individual’s peak pupil size across a task. That research had two limitations that needed to be addressed: the use of pixels (an unstandardized pupil size measurement unit) as the primary metric and the lack of inclusion of a pre-stimulus baseline period. Ninety-two Navy and Marine Corps student pilots performed a spatial orientation aptitude test while their pupillary data were recorded. Notably, a new technique was used to convert pupil data from pixels to millimeters and a pre-stimulus baseline period was added between trials to capture tonic activation. Results revealed that peak pupil sizes significantly reduced across trials (r = -.80). The relationship was still very strong after accounting for a reduction in pupillary tonic activation across trials (r = -.59). These findings provide strong support for prior research that showed that reductions in maximum pupil size can demonstrate learning across trials while completing a task. Importantly, this work improved and extended that research by confirming the results using millimeters, a standardized unit of pupil size, instead of pixels, and accounting for tonic activation.