Infants show pupil dilatory responses to happy and angry facial expressions

Facial expressions are one way in which infants and adults communicate emotion. Infants scan expressions similarly to adults, yet it remains unclear whether they are receptive to the affective information they convey. The current study investigates 6-, 9- and 12-month infants' (N = 146) pupillary responses to the six "basic" emotional expressions (happy, sad, surprise, fear, anger, and disgust). To do this we use dynamic stimuli and gaze-contingent eye-tracking to simulate brief interactive exchanges, alongside a static control condition. Infants' arousal responses were stronger for dynamic compared to static stimuli. And for dynamic stimuli we found that, compared to neutral, infants showed dilatory responses for happy and angry expressions only. Although previous work has shown infants can discriminate perceptually between facial expressions, our data suggest that sensitivity to the affective content of all six basic emotional expressions may not fully emerge until later in ontogeny.