Perceptual decisions require the accumulation and integration of noisy sensory information, and therefore perceptual decisions usually develop gradually 23, 24.
For instance, a study reported that pupil dilation predicted the stability of decisions under perceptual rivalry 22. The link between neuromodulatory activity and pupil size allowed other studies to show associations between pupil dilation and performance in attentional tasks 19, visual discrimination 20, and the speed of visual perceptual choices 21. This cholinergic activity was also shown to influence pupil dilation 18. In addition, recent studies point out a correlated activity between noradrenergic and cholinergic activity in regulating neural states such as alertness 17. The LC is thus believed to exert wide brain modulation of behavioral decisions 3, 4. The LC is the main noradrenergic nucleus in the brain, which sends projections to several cortical regions. Accumulating evidence shows that, under isoluminance conditions, changes in pupil size can be attributed almost exclusively to noradrenaline (NE) release from the locus coeruleus (LC) 16. However, emotional vocalizations are perceptual stimuli that require sensory integration in order to be decoded 7, 12, 13, 14, which may make it cognitively demanding to identify the emotional state of the speaker.Īpart from emotional stimuli, cognitively effortful tasks have long been known to influence pupil size 15.
UNEQUAL PUPIL SIZE BUT CONSTRICT EQUALLY SKIN
This view is supported by findings showing that pupil dilation correlates with measures of arousal such as skin conductance 2, and that stimuli portraying sexual content trigger especially large pupil responses 10, 11. 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. Within emotional stimuli, 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 equally large pupil responses 1, 2. Previous studies report that emotionally arousing stimuli, both auditory and visual, trigger bigger increases in pupil size than emotionally neutral stimuli 1, 2.
Because recent evidence suggests that emotion processing recruits cortical regions normally associated with cognition 5, 6, 7, in this study we investigate whether pupil responses can be used to betray the underlying process of affective processing. On the other hand, changes in pupil size are known to be linked to cognitive processing 3, 4 during tasks that do not involve emotional stimuli. These pupillary responses were therefore described as reflecting autonomic arousal triggered by emotional stimuli 1, 2. When individuals are exposed to affective signals such as nonverbal emotional vocalizations, their pupils usually increase in size as the stimuli are perceived. 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. 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. In addition, pupil response revealed properties of the decisions, such as the perceived emotional valence and the confidence in the assessment. In particular, peak pupil dilation betrayed the time of emotional selection. The results showed that during emotion recognition, the time course of pupil response was driven by the decision-making process. Participants heard human nonverbal vocalizations (e.g., laughing, crying) and indicated the emotional state of the speakers as soon as they had identified it. Therefore, in this study we investigated the relationship between pupil size fluctuations and the process of emotion recognition. Additionally, changes in pupil size were associated with decision making during non-emotional perceptual tasks.
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.
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