608 t-tests revealed that for the Adult Group the Imitation Effect was signiﬁcantly greater for the Pro-social Group (Mean = 71.11, SEM = 11.79) than for the Non-social Group (Mean = 37.98, SEM = 7.19; t(54) = -2.40, P \ 0.01, 1-tailed). No such signiﬁcant difference between Prime Groups existed for the Adolescent Age Group (Fig. 2: Pro-social: Mean = 37.98, SEM = 9.23; Non-social: Mean = 50.62, SEM = 11.99; t(32) = 0.84, P = 0.41). Hence, social priming differentially affected imitation in adolescents and adults. Speciﬁcity of social priming effects on mechanisms of imitation Paired samples t tests on compatible and incompatible RTs for Effector Priming Control trials demonstrated that each of the four groups exhibited a signiﬁcant Effector Priming Effect (Adolescent Non-social Group incompatible trials mean RT (SEM) = 570.91 (21.42), compatible trials mean RT (SEM) = 532.36 (19.73), t(16) = 4.81, P \ 0.001, 1-tailed; Adolescent Pro-social Group incomp mean RT (SEM) = 540.04 (17.81), comp mean RT (SEM) = 504.82 (19.76), t(16) = 3.81, P \ 0.01, 1-tailed; Adult Non-social Group incomp mean RT (SEM) = 532.22 (15.61), comp mean RT (SEM) = 482.77 (13.44), t(27) = 5.97, P \ 0.001, 1-tailed; Adult Pro-social Group incomp mean RT (SEM) = 571.12 (29.59), comp mean RT (SEM) = 515.57 (20.91), t(27) = 3.74, P \ 0.001, 1-tailed). That is, for each group, responses were faster when the same ﬁnger changed colour than when a different ﬁnger changed colour. Data from the Imitation task show that adult participants are signiﬁcantly affected by social priming, but that ado- lescent participants are not. In order to conﬁrm that the social priming effect on imitation seen in adults is speciﬁc Exp Brain Res (2011) 211:601–612 to imitation (as found by Leighton et al. 2010), we con- ducted a 2 9 2 ANOVA with between-subjects factor Prime Group (Pro-social, Non-social) and within-subjects factor Experimental Task (Imitation task, Effector Priming Control task) for the Adult Group. There was a signiﬁcant interaction between Prime Group and Experimental Task (F(1,54) = 2.89, P \ 0.05, 1-tailed). The same analysis conducted on the Adolescent Pro- and Non-social Groups (which do not differ in terms of imitation) did not show a signiﬁcant interaction (F(1,32) = 0.30, P = 0.58). T-tests showed that for the Adult Group the interaction was driven by a signiﬁcant difference in the magnitude of the Imitation Effect for the Pro-social (Mean = 71.11, SEM = 11.79) compared to Non-social Group (Mean = 37.98, SEM = 7.19; t(54) = -2.40, P \ 0.01, 1-tailed) but no signiﬁcant difference between the Prime Groups in terms of the Effector Priming Effect (Fig. 3: Pro-social: Mean = 55.55, SEM = 14.84; Non-social: Mean = 49.44, SEM = 8.28; t(54) = -0.36, P = 0.36). The three-way interaction between Prime Group (Pro-social, Non-social), Age Group (Adolescent, Adult) and Experimental Task (Imitation task, Effector Priming Control task) approached signiﬁcance (F(F(1,86) = 2.22, P = 0.07, 1-tailed). The preceding analyses were repeated on the raw RT data, including a repeated measures factor of Compatibility (Compatible, Incompatible) in order to assess whether Prime Group, Age Group, or the interaction between these factors affected RT irrespective of Compatibility. These effects were all non- signiﬁcant (all Ps [ 0.1). In order to assess the mechanism by which social priming affects imitation, the relationship between response speed and the social priming effect in each age group was examined. Reaction times were sorted according to the factors of Compatibility, Age Group and Prime Group and independently separated into three time bins, representing fast, medium and slow responses. The Fig. 2 Imitation Effects for Adolescent and Adult Pro- and Non- social Prime Groups. The ANOVA revealed a signiﬁcant interaction between Age and Prime Group. Post hoc t tests revealed that for the Adult Group the Imitation Effect was signiﬁcantly greater for the Pro- social Group than for the Non-social Group. No such signiﬁcant difference between Prime Groups existed for the Adolescent Age Group 123 Fig. 3 For the Adult Group, there was a signiﬁcant difference in the magnitude of the Imitation Effect for the Pro-social compared to Non- social Prime Group but no signiﬁcant difference between the Prime Groups in terms of the Effector Priming Effect