Pupil Diameter during Counting Tasks as Potential Baseline for Virtual Reality Experiments

Pupil diameter is a reliable indicator of mental effort, but it must be baseline corrected to account for its idiosyncratic nature. Established methods for measuring baselines cannot be applied in virtual reality (VR) experiments. To reliably measure a pupil diameter baseline in VR, we propose a short testing environment of visual arithmetic tasks. In an experiment with 66 university students, we analyzed external reliability and internal validity criteria for pupil diameter measures during counting and summation tasks. During the counting task, we found a high retest reliability between stimulus intervals. Acceptable retest reliability was found for task repetition at a second measuring time. Analyzing internal validity, we found that pupil diameter increased with task difficulty comparing both tasks. Further, a linear effect was found between the pupil diameter amplitude and luminance levels. Our findings highlight the potential of counting tasks as a pupil diameter baseline for VR experiments.