Pupillary Light Reflex Correction for Robust Pupillometry in Virtual Reality

Virtual reality (VR) headsets with an integrated eye tracker enable the measurement of pupil size fluctuations correlated with cognition during a VR experience. We present a method to correct for the light-induced pupil size changes, otherwise masking the more subtle cognitively-driven effects, such as cognitive load and emotional state. We explore multiple calibration sequences to find individual mapping functions relating the luminance to pupil dilation that can be employed in real-time during a VR experience. The resulting mapping functions are evaluated in a VR-based n-back task and in free exploration of a six-degrees-of-freedom VR scene. Our results show estimating luminance from a weighted average of the fixation area and the background yields the best performance. Calibration sequence composed of either solid gray or realistic scene brightness levels shown for 6 s in a pseudo-random order proved most robust.