Automated tracking of behavioural synchrony in cooperating marmosets

Abstract

Interacting humans tend to align with each other at physiological, neural and behavioural levels. The degree to which behaviours in an interaction are patterned or synchronised in both timing and form is termed behavioural synchrony. The degree of behavioural synchrony often correlates with cooperation, prosocial behaviour, and social cognition in human interactions. Intense cooperation and proactive prosociality have convergently evolved in humans and cooperatively breeding common marmosets, which makes them a great model to study the mechanisms underlying social cognition. Marmosets regularly engage in cooperative tasks, but it is not known if they too exhibit behavioural synchrony to facilitate coordination. It is also challenging to define and objectively evaluate behavioural synchrony and posture imitation in non-human animals. Here, we conducted an experiment to study behavioural synchrony in marmoset dyads before and after they engage in a prosocial task to investigate the effect of prosociality on behavioural synchrony. We established a pipeline to extract trajectories of multiple marmosets from video recordings. As a part of the pipeline, we first tracked the body parts of marmoset dyads from different angles using DeepLabCut, a markerless, automated, machine-learning-based pose estimation tool. We then used MATLAB’s stereo-camera calibration to reconstruct 3D coordinates of the marmoset body parts. With this pipeline, we examined the gaze direction and kinematics of marmoset hand movements during the task. We found that marmoset dyads mostly look in the same direction and exhibit distinct gaze patterns across different task conditions. We used dynamic time warping to analyse similarity in hand movements and found that individuals have more consistent patterns of task execution within themselves when compared to dyads. However, we did not find greater similarity in task kinematics of real dyads as compared to pseudo-dyads. Further studying the processes of synchronisation in freely moving marmosets will help us understand the overlap of proximate mechanisms regulating cooperation and social cognition in humans and marmosets.