Cognitive Stress Responses During an N-Back Task: Pupillary Dynamics and Salivary Alpha-Amylase Activity

Pupil area reflects not only the light reflex but also cognitive activity and arousal, and has been proposed as a non-invasive indicator of stress. However, the temporal characteristics of pupillary responses during cognitive stress tasks and their associations with other physiological and psychological measures remain unclear. This study examined cognitive stress responses during an N-back task using pupil area and changes in salivary alpha-amylase (sAA). Twenty-nine university and graduate students (mean age = 21.07 ± 0.91 years; 4 males, 25 females) participated. Pupil area was continuously recorded during a 2-back task. Salivary alpha-amylase was measured before (pre) and immediately after the task (post), and the change in sAA (post–pre) was calculated. Subjective stress responses and mood states were assessed using the SRS-18 and TDMS. A notable gender imbalance (predominantly female) limits the generalizability of findings, and future studies should aim for more balanced samples. Pupil area significantly decreased in the latter half of the task, consistent with a time-on-task effect. Although sAA showed no significant group-level change (BF10 = 0.25, indicating evidence for the null hypothesis), individual differences in the change in sAA (post–pre) were evident. Task accuracy and the change in sAA were associated with subjective measures of mood and stress. These findings suggest that cognitive stress is reflected differently across pupil area, changes in sAA, and subjective measures, highlighting the value of integrating multiple physiological and psychological indicators.