Pupil Constrictions and Their Associations With Increased Negative Affect During Responses to Recalled Memories of Interpersonal Stress

Pupil diameter change is indicative of emotional processing. Most previous findings regarding pupillary response and emotion have reported that the pupil enlarges in response to the presentation of emotional perceptual stimuli (e.g., visual images) within several seconds. It is considered that such stimuli activate the sympathetic nervous system, leading to pupil dilation. In order to examine the effects of emotions similar to daily emotional experiences of mood, the present study examined pupil diameter changes and their relationships with subjective emotional changes while recalling a topic of stressful interpersonal events in daily life. The data of 20 university students (11 males, M-age = 20.36 +/- 2.38 years: 9 females, M-age = 22.33 +/- 3.57) were analyzed. In the experimental task, participants were instructed to recall their memories concerning the topic through instructions and questions presented on a monitor, which proceeded at their own pace, through a key press. Subsequently, after baseline and instruction periods, participants were instructed to freely recall their memories. They were then asked to respond silently to a series of questions concerning the freely recalled memories. In the analysis, we compared the pupil diameters between these different periods and observed that pupil diameters significantly decreased during the response period relative to the free recall or baseline periods. Furthermore, pupil constrictions during the response period were negatively correlated with increases in negative affect scale scores. Pupil constriction, which is indicative of decreased arousal level and parasympathetic activation, was presumably caused by multiple factors including less cognitive difficulty and a relatively long experimental task period. As the result of a less tonic mode in the response period, the attention of participants might be more successfully focused on ongoing tasks, which might lead to optimal performance in recalling memories, possibly leading to correlations between pupil diameter and negative emotional changes.