540 attention effect held when trials of the 180 rotation con- dition were excluded from the analysis. The aim of the present experiment was to examine whether social context modulates this effect. We found that the slope of the rotation curve in the joint condition was ﬂattened in both the cooperative and the competitive set- ting and that there was no interaction of group and attention condition. Thus, the type of social interaction between participants did not change the effect of the other’s atten- tion. Even when the social context called for concentrating on one’s own performance (competition group), partici- pants could not help taking the other’s perspective into account. This suggests that joint attention in both social contexts led participants to adopt an allocentric frame of reference. However, social setting affected general performance. Participants in the cooperation group were generally slower than participants in the competition group. Competing against each other led to faster RTs than collaborating, suggesting that participants complied with the instructions. Contrary to experiment 1, intercepts for the single and the joint-attention condition only differed marginally in experiment 2. Thus, although participants beneﬁted from the other’s attention when stimuli were rotated towards the other, they were not slowed down as much by the other’s attention on non-rotated stimuli. This ﬁnding may be explained by the assumption that participants were highly focused on speeding up their responses because speed was rewarded in both groups. As the non-rotated stimuli were the easiest ones, they were the obvious candidates for speeding-up without making more errors. The attempt to respond as fast as possible might have prevented responses to non-rotated stimuli from being slowed down by the other’s attention. Taken together, the effect of joint attention on mental rotation ﬁrst observed in a neutral setting seems quite robust as the effect of joint attention on larger angles of rotation could be replicated in both a competitive and a cooperative setting. This effect seems best explained by the assumption that joint attention leads participants to adopt an allocentric reference frame. 3rd PP trials As in experiment 1, no systematic relation between degrees of rotation and RTs was found in 3rd PP trials and except for faster responses in 0 trials performance curves were rather ﬂat. Presenting initial hands in a third-person per- spective may have primed participants to adopt an allo- centric reference frame. As in the previous experiment, participants may have mapped stimuli in parallel onto their own and the other’s body axis. This would explain why, again, participants did not speed up when the second hand 123 Exp Brain Res (2011) 211:531–545 ﬁt their own body posture and were slower to respond to 0 trials in 3rd PP condition than in the 1st PP condition. As for 1st PP trials, participants were signiﬁcantly faster in joint-attention trials compared to single-attention trials in the competitive setting, implying that participants followed the instructions. Experiment 3 The third experiment aimed at clarifying the mechanisms underlying the effect of joint attention on the slope of the rotation curve. The ﬂattening of the rotation curve in the joint condition can be explained by assuming that joint attention leads participants to abandon their egocentric reference frame and to adopt an allocentric reference frame in order to transform the hand picture. The task we employed may have primed an allocentric perspective because on half of the trials, the initial hand picture was seen from the other’s ﬁrst-person perspective (implying a third-person perspective for the participant). This raises the question of whether effects of the other’s attention are stronger after priming an allocentric frame of reference. Previously, it has been reported that some brain areas have a preference for processing allocentric over egocentric views of bodies (Chan et al. 2004) and body parts (Saxe et al. 2006). Seeing a hand from a third-person perspective may prime a tendency towards interpreting stimuli within an allocentric reference frame. Are people more prone to taking the co-actor’s perspective into account after seeing a hand picture displayed from a third person, allocentric view? To keep the task as similar as possible to the two previous experiments, we manipulated the perspective of the initial hand picture in a given trial (ﬁrst person vs. third person; see Fig. 5) and studied how this affected performance on sub- sequent trials. The underlying logic of manipulating the orientation of the initial picture on a trial and studying the effect on a subsequent trial is as follows. If the initial hand picture were always seen from one’s own perspective, there would be no reference to the other’s perspective at all. In contrast, if the initial hand picture were always seen from the other’s perspective, there would be a strong emphasis on the difference in perspectives. Thus, varying the orientation of the initial hand picture in the preceding trial is an effective way of manipulating the reference to the other’s perspective and of priming an allocentric reference frame. If an allocentric perspective can be primed, seeing the initial hand picture in the preceding trial from a third- person view should enhance the joint-attention effect. In contrast, seeing the initial picture from one’s own per- spective should lead to a reduced joint-attention effect in the subsequent trial.