Exp Brain Res (2011) 211:531–545 3rd PP trials In 3rd PP trials (where the initial hand picture was rotated by 180 ), no systematic relation between degrees of rota- tion and RTs was found, except for faster responses to pictures showing the same degree of rotation as the initial hand. This suggests that beyond 0 trials (which may have been faster due to a perceptual beneﬁt of seeing the same position twice), participants neither selectively engaged in mentally aligning all second-hand picture with the initial hand picture (180 ), nor in aligning them with their own hand (0 ). Presenting initial hands in a third-person per- spective may have primed participants to adopt an allo- centric reference frame (note that stimuli seen from a third- person perspective are often referred to as ‘allocentric’; e.g., see Saxe et al. 2006; Vogeley and Fink 2003). While the initial hand (rotated by 180 ) highlighted the other’s body axis, the second hand highlighted participant’s own body axis, especially when there were large rotations rel- ative to the initial hand. This might have elicited a parallel mapping of the second hand onto the other’s body axis and the participant’s own body axis. The results are in line with this assumption because participants never completely ignored the other’s body frame, even when performing trials where the second-hand picture was fully aligned with their own body (180 s). Accordingly, responses in these trials were quite slow in 3rd PP trials (904 ms) as com- pared to 1st PP trials (734 ms). At the same time, partici- pants never neglected their own body frame, as noticeable in slower responses to no-rotation trials in 3rd PP trials (836 ms) as compared to 1st PP trials (734 ms). Given that participants in 3rd PP trials did not adopt an egocentric reference frame to begin with, joint attention could not further modulate the mental transformations employed to solve the task. Experiment 2 The aim of experiment 2 was to investigate whether task context modulates the inﬂuence of the co-actor’s perspective on mental transformation. Recent evidence suggests that in competitive situations, participants focus on their own per- formance and ignore their co-actor. Bekkering and colleagues found that participants processed their partner’s errors like their own only in a cooperative, but not in a competitive setting (Bekkering et al. 2009). Although error processing is thought to occur early and automatically, the social setting modulated how other people’s errors were processed. We manipulated social context in order to test whether the effect of joint attention observed in experiment 1 is sensitive to the type of social interaction participants are engaged in. If the tendency to adopt an allocentric 537 reference frame depends on social context, the effect of the other’s perspective should be more pronounced in one of the two settings. If, by contrast, the effect of joint attention is immune to social context, it should be found in both a competitive and a cooperative setting. Methods Participants Twenty-six same-sex pairs of undergraduate students par- ticipated in the experiment and received course credits or payment for participation. They were fellow students or friends and were randomly assigned to the two social context groups (13 pairs participated in the competition condition, 13 pairs in the cooperation condition). There were no differences in mean age, gender and handedness between groups (cooperation group: 21 female, mean age: 21.0, 3 left-handed; competition group: 20 women, mean age: 21.6, 4 left-handed). All of them reported normal or corrected-to-normal vision and signed informed consent prior to the experiment. Stimuli and procedure See experiment 1 Design The design was the same as in experiment 1, with the additional between-subject factor type of social interaction. Participants in the competition group were informed that the person with faster reaction times and fewer errors would be paid an extra 5 Euros. Participants in the coop- eration group were playing together against other pairs. Participants were informed that pairs that performed better than 50% of all other pairs would be paid an extra 5 Euros each. Thus, the chance of getting 5 Euros extra was as high in the competition group as in the cooperation group. To further emphasize individuality versus group belonging- ness, colours were assigned to either participants or groups (Patterson and Bigler 2007). Each participant in the com- petition group was assigned a different colour and so was each group in the cooperation condition. Data analysis The data were analysed in the same way as in experiment 1 (analysis of slopes and intercepts of the rotation curves with the factor attention condition). A 2 9 2 ANOVA with the between-subject factor type of social interaction and the within-subject factor attention was performed. As in Experi- ment 1, the main analyses included only 1st PP trials. 123