Abstract
Pupil contagion is the phenomenon in which an observer’s pupil-diameter changes in response to another person’s pupil. Even chimpanzees and infants in early development stages show pupil contagion. This study investigated whether dynamic changes in pupil diameter would induce changes in infants’ pupil diameter. We also investigated pupil contagion in the context of different faces. We measured the pupil-diameter of 50 five- to six-month-old infants in response to changes in the pupil diameter (dilating/constricting) of upright and inverted faces. The results showed that (1) in the upright presentation condition, dilating the pupil diameter induced a change in the infants’ pupil diameter while constricting the pupil diameter did not induce a change, and (2) pupil contagion occurred only in the upright face presentation, and not in the inverted face presentation. These results indicate the face-inversion effect in infants’ pupil contagion.
Highlights
An increasing body of evidence indicates that pupillary contagion is a social function that extends beyond mere physiological responses (Harrison et al, 2006; Kret et al, 2014, 2015; Prochazkova and Kret, 2017; Prochazkova et al, 2018)
Following the procedure of these studies, we examined this asymmetry in pupil contagion in dynamic changing pupil diameters in 5- to 6-month-old infants
There was no other significant main effect (pupil change direction: F(1,48) = 0.768, p > 0.1, η2 = 0.016) or interaction (F(1,48) = 0.224, p > 0.1, η2 = 0.0046). These results indicated that infant observed eye region on upright face more than that on inverted face
Summary
An increasing body of evidence indicates that pupillary contagion is a social function that extends beyond mere physiological responses (Harrison et al, 2006; Kret et al, 2014, 2015; Prochazkova and Kret, 2017; Prochazkova et al, 2018). Their study reported that infants at 4 and 6 months of age, when viewing the eye region of male and female adults with small, medium, or large pupils, showed pupil dilation in response to others’ large pupils, but not small or medium pupils (Fawcett et al, 2017). These studies showed that the schematic depictions of eyes or eye regions induces pupil contagion in infants and that infants’ pupil diameter dilate when infants observe stimuli with large pupils, whereas infants’ pupil diameter does not decrease when infants observe stimuli with small pupils. Pupil contagion shows an asymmetry between dilating and constricting pupil observation in infants
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