Effects of concurrent task difficulty and physical effort on memory and perceptual performance and pupil response in younger adults

In daily life, cognitively demanding tasks are often performed while simultaneously exerting physical effort, yet the few studies that have examined their combined impact on performance have been limited to the working memory domain. This study systematically examined effects of concurrent task difficulty (Easy vs. Hard stimulus similarity) and physical effort (Low vs. High handgrip) on both behavioral performance and task-evoked pupil response in three cognitive tasks (visual working memory, auditory perception, visual perception) in healthy younger adults. Results revealed main effects of task difficulty on performance in all tasks, with participants being less accurate and slower in the Hard vs. Easy condition, and a main effect of physical effort on performance in the visual perception task, with participants being slower under High relative to Low effort. However, there were no interactions between task difficulty and physical effort for any task or performance metric. The pupil response showed only significant main effects of physical effort for all tasks, with larger pupil response during High vs. Low effort conditions. Individual-level analyses also revealed no significant correlations between these behavioral and pupillary responses. Overall, our findings do not support the notion that task difficulty and physical effort draw on common limited-capacity resources or that they similarly impact pupillary arousal, at least for the levels used here in healthy young adults.