Pupillometry as a window to detect cognitive aging in the brain.

This study investigated whether there are aging-related differences in pupil dilation (pupillometry) while the cognitive load is manipulated using digit- and word-span tasks. A group of 17 younger and 15 cognitively healthy older adults performed digit- and word-span tasks. Each task comprised three levels of cognitive loads with 10 trials for each level. For each task, the recall accuracy and the slope of pupil dilation were calculated and analyzed. The raw signal of measured pupil size was low-pass filtered and interpolated to eliminate blinking artifacts and spike noises. Two-way ANOVA was used for statistical analyses. For the recall accuracy, the significant group differences emerged as the span increases in digit-span (5- vs. 7-digit) and word-span (4- vs. 5-word) tasks, while the group differences were not significant on 3-digit- and 3-word-span tasks with lower cognitive load. In digit-span tasks, there was no aging-related difference in the slope of pupil dilation. However, in word-span tasks, the slope of pupil dilation differed significantly between two groups as cognitive load increased, indicating that older adults presented a higher pupil dilation slope than younger adults especially under the conditions with higher cognitive load. The current study found significant aging effects in the pupil dilations under the more cognitive demanding span tasks when the types of span tasks varied (e.g., digit vs. word). The manipulations successfully elicited differential aging effects, given that the aging effects became most salient under word-span tasks with greater cognitive load especially under the maximum length. Supplementary Information: The online version contains supplementary material available at 10.1007/s13534-023-00315-6.