Representing strangers in personal space triggers coding of defensive hand movement.

Our brain codes manipulable tools as possibilities for action, particularly for those surrounding the body. Recent studies showed people would adjust their motor program when observing others around their own bodies (i.e. in the personal space). However, it remained unclear whether representing a personal space invader can automatically trigger motor coding. To address this, we devised an interaction task to measure the activation of pushing movements in facing a stranger approaching into personal space. The LRP (lateralized readiness potential) analyses revealed that observing a stranger in personal space caused an initial LRP bias associated with pushing movements, and an LRP deflection before responding of pull, suggesting representing personal space invaders activated the motor coding of push. The behavioral results showed the personal space intrusion prolonged the reaction time of participants' subsequent instructed pulling responses. The results of experiment 2 confirmed the behavioral observation of experiment 1 and further revealed the relationship between the response bias of push and social anxiety. Together, the present study demonstrates representing a stranger in personal space activated coding of defensive hand movements and biased subsequent motor responses.