Abstract
The processing of emotional signals usually causes an increase in pupil size, and this effect has been largely attributed to autonomic arousal prompted by the stimuli. Additionally, changes in pupil size were associated with decision making during non-emotional perceptual tasks. Therefore, in this study we investigated the relationship between pupil size fluctuations and the process of emotion recognition. Participants heard human nonverbal vocalizations (e.g., laughing, crying) and indicated the emotional state of the speakers as soon as they had identified it. The results showed that during emotion recognition, the time course of pupil response was driven by the decision-making process. In particular, peak pupil dilation betrayed the time of emotional selection. In addition, pupil response revealed properties of the decisions, such as the perceived emotional valence and the confidence in the assessment. Because pupil dilation (under isoluminance conditions) is almost exclusively promoted by norepinephrine (NE) release from the locus coeruleus (LC), the results suggest an important role of the LC-NE system during emotion processing.
Highlights
Imagine that you hear someone yelling in pain, or laughing: these emotional vocalizations may often carry no linguistic content, yet they convey immediate information about the emotional state of the speaker
As the perception of emotional states seems to depend on interactions between cortico-emotional regions, we expect that pupil dilation should reflect both dimensions of emotion processing
We investigate whether pupil responses reflect cognitive and attentional mechanisms inherent in emotion processing
Summary
Imagine that you hear someone yelling in pain, or laughing: these emotional vocalizations may often carry no linguistic content, yet they convey immediate information about the emotional state of the speaker. Some authors[8,9] found that negatively valenced stimuli (e.g., crying) trigger larger pupil dilations than positive stimuli (e.g., laughter), whereas others found that both positive and negative stimuli could generate large pupil responses[1,2] Despite some discrepancies, this evidence led to interpret pupillary responses as autonomic reactions elicited by arousing stimuli[1,2] rather than as a reflection of cognitive emotional processing. We investigate whether pupil responses reflect cognitive and attentional mechanisms inherent in emotion processing (in addition to simple autonomic responses to arousing stimuli, as previously reported) For this purpose, participants were exposed to naturalistic human vocalizations while they were eye-tracked under isoluminance conditions. We show that pupil dilations are not the product of emotional responses, but a rich source of information about affective processing, which opens new avenues for emotion processing research
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