Discrimination between biological motion with and without social intention: a pilot study using visual scanning in healthy adults

Human beings have a detailed understanding of others' action and body language allowing them to adapt their behaviour for effective social interaction. A proper selection of human motion deserving a social intention over the many human motion surrounding them may be executed by overt visual-spatial attention. The aim of this study was to characterize eye movements in 32 healthy adults while exploring Social and Non-social human biological motion using an eye tracking method according to two paradigms. The "preferential looking paradigm" revealed that the first fixation is more often on the Non-social Motion than Social Motion but the first fixations duration are longer on Social Motion. Moreover, with the same paradigm, subjects spent a greater looking time percentage on Social Motion than Non-social Motion, no matter whether discrimination between categories was asked for or not. In the "blocks paradigm" the looking time percentage varied by the body parts (chests, pelvis and legs) and its distribution was different between categories. Eye movements revealed a spontaneous, fast and durable bias of overt visual-spatial attention favouring the perception of Social Motion and a different visual scanpath for Social compared to Non-social human biological motion. These findings constitute a basis for the investigation of a 'social intention' bias in perception of human biological motion.