Social modulation of spatial judgment as assessed by line bisection task taken in turn

Our actions are influenced by the social context in which they are performed, specifically it has been shown that observing others' actions influences the execution of the same action. In the present study, we examined whether and to what extent observers are influenced by the presence and performance of another person in a visual spatial task, using a line bisection paradigm in which two participants performed the task in turns while sitting in front of each other. Thirty pairs of participants took part in the experiment, which was divided into a non-social and a social session. In the latter, each participant was alternately an agent (performing the task) and an observer (evaluating covertly the other's performance). Results show that the leftward bias (pseudoneglect) in the line bisection task was significantly reduced when the task was performed in the social session, although the bias (both in the non-social and in the social session) was observed only when the left hand was used. Moreover, a dissociation between performance and perception was observed: the judgment given to the other's performance (which visually deviated in the direction opposite to one's own bias due to the spatial arrangement of participants and their facing vantage points) was significantly in disagreement with one's own performance. Overall, our results demonstrate that the other's presence influences our own action during a line bisection task and that spatial judgments on other's performance can modulate our own performance, even when coordination between participants is not required. Results are discussed in relation to social influence and perspective taking in the general framework of interpersonal resonance.