Task-invoked pupillary response
Task-invoked pupillary response (also known as "Task-Evoked pupillary response") is a pupillary response observed after an increase in cognitive load in humans, as a result of the subsequent decrease in parasympathetic activity in the peripheral nervous system. As a task places increased demand on working memory, pupil dilation has been observed to increase linearly.
Source: Wikipedia — Task-invoked pupillary response (CC BY-SA 4.0)