Expectations Of Other People’s Future Behavior Influence Current Grasping Movements

Perceiving the behavior of others and anticipating their future behavior is an essential process in social interaction.Generally,the expectation is in accordance with the law of motion.Previous studies have confirmed that observing others’ grasping movements has an impact on current grasping actions,however,in most of these studies,individuals are able to observe the target and the grasping execution stage of others.In this study,we aim to explore that when observing the grasping movement of others,with the grasping target and the grasping movement of others blocked,whether individuals can automatically complete other people’s movements according to the motion law and the pre-grasping stage;whether this process can affect the current grasping.These issues are discussed based on Fitts’ law;it is not only helpful to explore characteristics and mechanisms of the impact of motion perception on the action,but also helps to supplement the knowledge of the interaction between individuals and others in a social environment.This study consists of four experiments.Experiment 1 aims to demonstrate the relationship between Fitts’ law and grasping.In order to study grasping based on Fitts’ law,it first needs to know whether grasping conforms to Fitts’ law.Participants were required to actively grasp the target with a quick or slow speed.Results revealed that the peak grip aperture is significantly larger with fast speed than that with slow speed;it proves grasping conforms to Fitts’ law.Experiment 2 is conducted to investigate whether the individual can automatically complete the observed action;whether the current grasping would be affected by observing other people’s grasping with the target blocked.Participants were required to judge the movement speed of experimenter(fast,slow),at the same time,according to the speed,participants need to perform a power grip or a precision grip.Results showed that the peak grip aperture is significantly larger when observing fast speed than that when observing slow speed;it demonstrates that the current grasping is influenced by observing others’ behavior,even if the grasping target of others and the process of interaction with the object cannot be seen.Experiment 3 aims to explore the mechanism which affects the current grasping.We assume that after observing the speed in the early stage of grasping of others,individuals can automatically complete the later stage of grasping of others based on Fitts’ law.Expectations for the future behavior of others affect the current grasping.But here,a possibility,individuals could imitate others’ speed,will also have an impact on the current grasping and cannot be ruled out.In order to explore the specific mechanism,Experiment 3 excludes the reach stage of grasping to eliminate the speed imitation,and adds the estimation task.It is found that observing others’grasping speed has an effect on the current grasping task as well as on the estimation task.Results demonstrate that the influence mechanism,which lies in the expectation of future behavior of others,affects action execution and action planning.Experiment 4 is intended to further prove the reliability of expectation mechanism.Participants were required to observe the moving speed of the square block which presented on the screen,and grasp the real target object.Results showed that the speed of square block has no effect on the current grasping movement;it demonstrates that individuals do not generate expectations according to the speed of the square block,and it further indicates that observing the movement speed of others affecting the current grasping movement is mainly attributed to the expectation mechanism.This study shows that grasping conforms to Fitts’ law;observing the speed of others’ grasping movement has an impact on the current grasping movement,even the grasp execution stage of other people is blocked.Individuals will anticipate the future behavior of others,and this process internalizes the physical laws of motion control,thus,affects the current grasping movement.