Figure 1

(a) We observed daily infant-parent interaction using head-mounted eye trackers worn by the parents. The infants and parents could move freely in their home environment. (b) Image from the scene camera of a head-mounted eye tracker worn by a parent. The red circle in the image represents the parent’s gaze fixation. Continuous images with infant gaze directed to the parent and the parent gaze on the infant’s face were defined as an eye contact bout (EC bout). (c) There were two types of EC bouts: infant-led EC bout (blue) and parent-led EC bouts (light green). We defined a series of EC bouts with short inter-eye-contact-bout intervals (IEI) as an eye contact session (EC session; green).