Facial expressions of emotion are infrequent in toddlers' and caregivers' egocentric views. An ecological study.

Toddlerhood is a critical period in the development of facial expression processing. Prior research suggests that in the natural environment, the frequency of faces in the toddlers' egocentric view declines relative to infancy. However, the specific statistics of the emotional facial expressions available to the developing toddler remain unknown. This study implemented a dual-perspective set-up to record the egocentric view of toddlers and their caregivers during everyday situations at home (N=26 families). Using automated computer vision models, we quantified both the frequency of faces and the emotional expressions displayed. Confirming our hypotheses, faces were sparse in toddler views and significantly less frequent than in caregiver views. Across both perspectives, happiness was the dominant expression, while negative facial expressions were extremely rare. Notably, faces expressing surprise were frequent in toddler view, whereas caregivers encountered significantly more happy and sad facial displays than their children. Both faces and facial expressions were also temporally bursty in the two perspectives, clustering in time rather than occurring at random. This is the first ecological study to objectively quantify the occurrence of emotional facial expressions in the home environment. These findings challenge the assumption of an abundance of emotional signals in the early development. Instead, they demonstrate that toddlers develop face representations based on sparse input that is biased toward positive expressions (e.g., happy), suggesting high efficiency in extracting and generalizing information from limited input.