3. 4. Pupil diameter
The effect of stress induction on the average pupil diameter (see Figure 4B) was analyzed using a mixed-measures ANOVA with the factors Time (Ocular 1, Ocular 2, and Ocular 3) and Group (control group vs. stress group). No significant main effects of Time, F (2, 122) = 2.82,p = .007, \(\eta_{p}^{2}\) = 0.04, or Group, F (1, 61) = 2.36, p = .130, \(\eta_{p}^{2}\) = 0.04 were found. However, the interaction effect of Time × Group was significant, F (2, 122) = 4.52, p = 0.016, \(\eta_{p}^{2}\) = 0.07. Simple effects analyses (Bonferroni corrected) indicated that the pupil diameter in the stress group was significantly larger than that in the control group at the time point of Ocular 2 (p = .026).
To determine whether the pupil diameter changed during acute stress induction, an independent sample t-test was performed on the AUCi of pupil dilation. Significant differences in pupil dilation between the groups were observed, t (61) = 3.07, p = .003. The result revealed that calculating mental arithmetic tasks led to a significant increase in pupil dilation, confirming that pupil diameter varies with stressful arousal.