Table 2.

Descriptions of Measures of Coordination

Domain	Variable	Definition
Vocal Coordination
Cross-Recurrence Measures	Total Simultaneous Recurrence	Recurrence rate at lag 0; the total proportion of time mothers and infants spent vocalizing at the same moment
	Maximum recurrence within 5 second lag	Maximal recurrence rate to the right/left of 0, the maximum lagged match for Partner A’s vocalizations following Partner B’s vocalizations.
Event-based Measures	Frequency Contingency Response	Frequency Person B’s Vocalization follows offset of Person A’s within 2 seconds.
	Mean Latency to Respond	Mean latency between offset of Person A’s vocalization and onset of Person B’s vocalization
	Frequency Simultaneous Speech	Frequency Person B’s vocalization begins during Person A’s Vocalization
Gaze Coordination
Cross-Recurrence Measures	Total Simultaneous Recurrence	Recurrence rate at lag 0; the total proportion of time mothers and infants spent in simultaneous attention
	Mean recurrence within 5 second lag	Mean recurrence rate to the right/left of 0; the mean of all lagged matches for person A looking where person B was looking previously at varying degrees of lag up to 5 seconds.
Event-based Measures	Frequency follow to simultaneous attention	Frequency Person B looks to location Person A is looking (while Person A is still looking there).
	Mean latency follow to simultaneous attention	Mean latency between when Person A looks to a new location and Person B looks to that same location (while Person A is still looking there).