Shaozhe Cheng¹ (), Jingyin Zhu¹, Jifan Zhou¹, Mowei Shen¹, Tao Gao²; ¹Zhejiang University, ²UCLA

The abrupt onset of a new object is known to automatically capture human attention. In this study, we explore whether this visual cue's impact extends beyond individual attention, aiding in social coordination and joint planning. A key challenge in social coordination is the presence of multiple equally desirable targets, with the need for the team to commit to just one. But which one? We tested the hypothesis that in such joint planning tasks, where cooperation is visually guided, all players can spontaneously use the abrupt onset as a rallying point to jointly pursue the newly present target, instead of the old target that has lost its saliency. We used a collaborative Pac-Man task, where pairs of participants could only 'eat' an object on a 2D map by jointly navigating to it. At any moment, there were always two objects: one left-over from the previous navigation, and a new one that appeared abruptly at the moment participants jointly ate a current object. Results showed that participants were biased toward reaching the new object, even when the distance to both the old and new objects was controlled. We then explored whether this effect is specific to establishing a rally point in joint planning or it impacts group behavior through individual planning. An individual Pac-Man task showed an opposite bias: participants tended to eat the old object. Furthermore, in a relay task where two participants took turns controlling a single PacMan, as opposed to simultaneously controlling two PacMans, they again demonstrated a bias toward the old object. Collectively, these findings suggest that the unique challenges of group coordination allow the effect of abrupt onset objects to transcend individual attention, making visual salience a critical factor in facilitating the establishment of joint attention. This provides insight into the visually grounded nature of human cooperation.