<p>Summary of the findings in this study.</p>

Automated facial expression analysis provides an opportunity to study nonverbal behavior during naturalistic interactions in a more objective and continuous manner. We characterize dyadic facial synchrony from video-based facial action unit time series and examine its association with marital relationship quality.

Specifically, dyadic coordination is quantified using zero-lag cross-correlations between partners’ facial behaviors across multiple action units. Computed over successive temporal windows, these synchrony measures form a multidimensional synchrony profile, termed the S-matrix. We evaluate the proposed method using an iMotions dataset comprising video recordings of in-person conversations, frame-level facial expression estimates, and Quality of Marriage Index (QMI) survey responses from 27 married couples.