be compared to the visual feedback available during motor execution, and used for related online corrections (dashed lines in Figure 7; note, however, that these results do not rule out corrections based on kinesthetic input during execution [48]). By way of exclusion then, the present finding confirms that the observed distractor effects are primarily due to visuomotor interactions, as well as biased competition, during observation of the distractor actions. Finally, it is tempting to speculate about the possible neural substrate of the observed imitation bias in rhythmical actions. One piece of evidence comes from an unpublished pilot study on the imitation of rhythmical actions in a patient with visual form agnosia [49]. Despite the patient’s severe impairment of ventral visual stream function, D.F. [50] showed a remarkable accuracy in immediate unintended imitation of the (manipulated) cycle times in a variety of everyday actions (r = 0.90 between displayed and produced cycle times in the pilot study). It is thus conceivable that, in addition to information about action-relevant object properties, information about the temporal characteristics of an observed action is also initially processed via the dorsal visual stream (see also [51]). This does, however, not exclude that additional brain structures become engaged during covert simulation. Likely candidates involved in the observation and execution of rhythmi- cal actions are Broca’s area, the basal ganglia, and the cerebellum [52–53]. Conclusions In the present study we used everyday rhythmical actions to explore a core dimension of imitative alignment or ‘low-level motor resonance’ [8]. The main finding was a reliable bias in response cycle times as a result of the (task-irrelevant) modulation in distractor cycle times. This imitation bias was robust against manipulations of the time interval before motor execution and of visual monitoring of the hand during execution, where the latter indicates that this is a genuine visuomotor effect. Importantly, the imitation bias was still present, though attenuated, in the incompatible conditions where the distractor action was not useful for motor preparation. We submitted that these incompatible conditions provide a more cogent demonstration of automatic imitation than compatible conditions (as used, for e.g., by [20,23]), where distractor displays can principally be used to support motor preparation. That is, the distractor effects in the present incompatible conditions occurred even in a situation where References 1. Chartrand TL, van Baaren R (2009) Human mimicry. Adv Exp Soc Psychol 41: 219–274. 2. Vogt S, Thomaschke R (2007) From visuomotor interactions to imitation learning: Behavioural and brain imaging studies. J Sports Sci 25: 497–517. 3. Heyes CM (2011) Automatic imitation. Psychol Bull 137: 463–483. 4. Brass M, Bekkering H, Wohlschlager A, Prinz W (2000) Compatibility between observed and executed finger movements: Comparing symbolic, spatial, and imitative cues. Brain Cogn 44: 124–143. 5. Brass M, Bekkering H, Prinz W (2001) Movement observation affects movement execution in a simple response task. Acta Psychol 106: 3–22. 6. Stu¨ rmer B, Aschersleben G, Prinz W (2000) Correspondence effects with manual gestures and postures: A study of imitation. J Exp Psychol Hum Percept Perform 26: 1746–1759. 7. Vogt S, Taylor P, Hopkins B (2003) Visuomotor priming by pictures of hand postures: Perspective matters. Neuropsychologia 41: 941–951. 8. Rizzolatti G, Fadiga L, Fogassi L, Gallese V (2002) From mirror neurons to imitation: Facts and speculations. In: Meltzoff AN, Prinz W, editors. The imitative mind: Development, evolution, and brain bases. Cambridge: Cam- bridge University Press. 247–266. 9. Byrne RW, Russon AE (1998) Learning by imitation: A hierarchical approach. Behav Brain Sci 21: 667–721. 10. Bates LA, Byrne RW (2010) Imitation: What animal imitation tells us about animal cognition. Wiley Interdiscip Rev Cogn Sci 1: 685–695. Automatic Imitation in Rhythmical Actions participants had good reasons to minimise the impact of the observed distractor actions on their own motor preparation, in order to avoid confusion between the conflicting actions. Given that the effects of action and of plane compatibility were not additive, and that they were not found in intentional imitation, we favoured an account in which the distractor’s impact on motor processing can be generally reduced over an account where action and plane incompatibility reduce the imitation bias independently. Using Cisek & Kalaska’s [44] framework, we further conceptual- ised the suppression in incompatible trials as the result of a biased competition between the sensorimotor representations of distrac- tor and instructed action. The notion of a global suppression effect, where potentially all parameters of the observed action are affected, was principally supported by the fact that, although the conflict between distractor and instructed actions was only applied to action type and plane, the compatibility manipulations clearly affected an additional parameter, namely the cycle times. As such, our study is the first of its kind involving multiple compatibility dimensions and studying their interdependency. The results indicate a rather moderate kinematic fidelity between distractor and executed action, not unlike the modest modulations of reaction times in conventional automatic imitation paradigms [3]. Nevertheless, we hope that the present study paves the way for further investigations into competitive processes between quasi- encapsulated sensorimotor representations, as well as into the boundary conditions for both near-perfect imitative behaviour and the more moderate imitative biases found when strategic factors are carefully controlled. Acknowledgments This experiment was carried out by D. Eaves as part of his doctoral thesis under the supervision of S. Vogt and M. Turgeon. We would like to thank B. Usherwood (Lancaster University) for his kind help with the technical development of the setup used in this study, and A. Stebulitis (Teesside University) for his helpful guidance on video editing procedures. Author Contributions Conceived and designed the experiments: DE SV MT. Performed the experiments: DE. Analyzed the data: DE SV. Contributed reagents/ materials/analysis tools: DE SV. Wrote the paper: DE SV MT. Development of theoretical ideas: DE SV MT. 11. Buccino G, Vogt S, Ritzl A, Fink GR, Zilles K, et al. (2004) Neural circuits underlying imitation learning of hand actions: An event-related fMRI study. Neuron 42: 323–334. 12. Vogt S, Buccino G, Wohlschla¨ger AM, Canessa N, Shah N, et al. (2007) Prefrontal involvement in imitation learning of hand actions: Effects of practice and expertise. NeuroImage 37: 1371–1383. 13. Wohlschla¨ger A, Gattis M, Bekkering H (2003) Action generation and action perception in imitation: An instance of the ideomotor principle. Phil Trans Royal Soc B 358: 501–515. 14. Griffiths D, Tipper SP (2009) Priming of reach trajectory when observing actions: Hand-centred effects. Q J Exp Psychol 62: 2450–2470. 15. Ocampo B, Kritikos A (2010) Placing actions in context: motor facilitation following observation of identical and non-identical manual acts. Exp Brain Res 201: 743–751. 16. Kelso JAS (1995) Dynamic patterns. Cambridge: MIT Press. 17. Schmidt RC, Carello C, Turvey MT (1990) Phase transitions and critical fluctuations in the visual coordination of rhythmic movements between people. J Exp Psychol Hum Percept Perform 16: 227–247. 18. Schmidt RC, O’Brien B (1997) Evaluating the dynamics of unintended interpersonal coordination. Ecol Psychol 9: 189–206. 19. Oullier O, de Guzman GC, Jantzen KJ, Lagarde J, Kelso JAS (2007) Social coordination dynamics: Measuring human bonding. Soc Neurosci 3: 178–192. PLOS ONE | www.plosone.org 11 October 2012 | Volume 7 | Issue 10 | e46728