Overall patterns of coordinated attention.

1) proportion of joint attention measures the overall proportion of time that participants were in coordinated attention by the two definitions. 2) frequency of joint episodes measures the number of coordinated attention events per minute; and 3) mean duration captures the average duration of joint attention events (of synchronization without even momentary looks away, or the duration of longer sustained bouts of attention with potential looks away by a partner within that bout). For each measure, the results are further divided into an overall measure (counting all the joint attention moments including both shared attention on objects and on each other's face) and then the two components of that overall measure, shared attention to objects (counting only the moments of jointly attending the same object) and mutual gaze (counting only the moments of looking at each other's face).