Eye Synchrony: A Method to Capture Mutual and Joint Attention in Social Eye Movements.

Gaze behavior represents a complex phenomenon in social inter-action. We focus here on dyadic face-to-face interaction during naturally occurring verbal exchanges, where shared attention can be operationalized by joint gazes and eye contact. A multi-step methodology for the analysis of eye synchrony is presented, exemplified by a single case. The dynamics of face-to-face interaction allows estimating the degree of interlocutors' synchrony. While there is growing evidence for interpersonal synchrony of various behavioral and physiological signals, eye synchrony has not yet been studied outside the laboratory. The method presented is based on time series of gaze behavior acquired by mobile eye tracking devices. We applied windowed cross-correlations to the data and used surrogate testing to attain effect sizes even for single interactions (Surrogate Synchrony, SUSY). SUSY thus integrates nomo-thetic with idiographic research goals: The nomothetic interest is to test hypotheses that gaze behavior may be generally synchronized and linked with psychological variables. The idiographic aspect is that effect sizes can be determined even in single-case studies owing to the surrogate analyses, which supports qualitative research. Results of the exemplary dataset suggested that proof-of-concept of this approach was attained. We describe what prerequisites are needed of a setting and technical setup for use in future studies of psychotherapy, counseling, negotiations, or work-related interactions.