The visual stimuli attributes instrumental for collective-motion-related decision-making in locusts

Visual interactions play an instrumental role in collective-motion-related decision-making. However, our understanding of the various tentative mechanisms that can serve the visual-based decision-making is limited. We investigated the role that different attributes of the visual stimuli play in the collective-motion-related motor response of locust nymphs. We monitored and analyzed the behavioral responses of individual locusts tethered in a natural-like walking posture over an airflow-suspended trackball to carefully selected stimuli comprising various black rectangular shapes. The experimental findings together with a prediction model relating the level of behavioral response to the visual stimuli attributes indicate a major role of the number of objects in the visual field, and a further important effect of the object’s vertical moving edges. While the object’s horizontal edges can be utilized in the estimation of conspecifics’ heading, the overall area or visual angle subtended by the stimuli do not seem to play any role in inducing the response. Our results offer important novel insights regarding the fundamental visual-based mechanisms underlying animal collective motion and can be useful also in swarm robotics.