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).

1) 共同注意力比例（proportion of joint attention）：衡量被试依据两种定义达成协调注意力的总时长占比。2) 共同注意力片段频次（frequency of joint episodes）：衡量每分钟内协调注意力事件的发生数量；3) 平均时长（mean duration）：表征共同注意力事件的平均持续时长，既包含全程无短暂视线移开的同步注意力场景，也涵盖该注意力回合内搭档存在短暂视线偏移但仍维持的更长持续注意力时段。针对每一项指标，其结果会进一步划分为整体指标（统计所有共同注意力时刻，涵盖对物体的共同注意力以及对彼此面部的共同注意力），以及该整体指标的两个组成部分：物体共同注意力（仅统计双方共同注视同一物体的时刻）和互视（仅统计双方注视彼此面部的时刻）。