Imitative Response Tendencies Following Observation of Intransitive Actions Bennett I. Bertenthal, Matthew R. Longo, and Adam Kosobud University of Chicago Clear and unequivocal evidence shows that observation of object affordances or transitive actions facilitates the activation of a compatible response. By contrast, the evidence showing response facilitation following observation of intransitive actions is less conclusive because automatic imitation and spatial compatibility have been confounded. Three experiments tested whether observation of a finger move- ment (i.e., an intransitive action) in a choice reaction-time task facilitates the corresponding finger movement response because of imitation, a common spatial code, or some combination of both factors. The priming effects of a spatial and an imitative stimulus were tested in combination (Experiment 1), in opposition (Experiment 2), and independently (Experiment 3). Contrary to previous findings, the evidence revealed significant contributions from both automatic imitation and spatial compatibility, but the priming effects from an automatic tendency to imitate declined significantly across a block of trials whereas the effects of spatial compatibility remained constant or increased slightly. These differential effects suggest that priming associated with automatic imitation is mediated by a different regime than priming associated with spatial compatibility. Keywords: imitation, response priming, intransitive actions, common coding, mirror neurons The human tendency to mimic actions performed by others has long been noted in studies of normal and abnormal behavior. Charles Darwin (1872/1965), for example, commented that at leaping matches spectators would move their own feet as if imitating the athletes. More recently, Dijksterhuis and Bargh (2001) noted that we tend to whisper or speak louder when others do, scratch our head upon seeing some- one else scratch, walk slower in the presence of elderly individuals, and cycle faster after seeing a cycling race on TV. Evidence for automatic imitation has also been observed in pathological conditions, such as autism (Fay & Hatch, 1965), schizophrenia, and catatonia (Ford, 1991); certain abnormal startle reactions or hyperekplexias (Beard, 1880; Ford, 1991; Simons, 1980); Tourette’s syndrome (Ford, 1991; Gilles de la Tourette, 1884/1996); postepileptic or confusional states (Schneider, 1938; Stengel, 1947); dementia or mental retarda- tion (Dromard, 1905; Stengel, 1947); and following lesions of the frontal lobes (De Renzi, Cavalleri, & Facchini, 1996; Lhermitte, Pillon, & Serdaru, 1986). This automatic tendency may contribute to the “social glue” by which humans coordinate their behaviors, coop- erate, and develop affiliative tendencies toward each other (Chartrand & Bargh, 1999; Lakin, Jefferis, Cheng, & Chartrand, 2003). The prevailing interpretation for these effects is that the percep- tion of action automatically activates corresponding motor pro- grams in the observer. Darwin (1872/1965), for example, argued that in man, there is “a strong tendency to imitation, independently of the conscious will” (p. 355). To account for the occurrence of echopraxia in his patients, Dromard (1905) similarly suggested that “a movement that has been perceived tends to pass from the visual center to the motor center” (p. 389 [our translation]). He went further to propose that this latent imitation was an integral part of the mental representation of movement. In recent years, Prinz and colleagues (e.g., Prinz, 1990, 1997; Hommel, Mu ¨sseler, Aschersleben, & Prinz, 2001) proposed that observing the effect of an action facilitates its execution because perception and action planning share a common representational code. More specifically, the perception of an event possessing certain features (e.g., a loud sound) will automatically prime those actions that produce the same features (e.g., speaking in a loud voice). This formulation of a common coding framework for the perception and planning of actions is a direct descendent of the ideomotor theory of James (1890) and Greenwald (1970). Empirical Evidence for Common Coding Recent neurophysiological, neuroimaging, and behavioral re- search offer support for a common coding framework. The remark- able discovery of mirror neurons in monkeys provided the first direct evidence that action observation and action execution shared a common neural representation. Mirror neurons, located in ventral premotor area F5, discharge both when the monkey performs specific goal-directed actions and when the monkey observes a human or conspecific perform the same or a similar action (di Bennett I. Bertenthal, Matthew R. Longo, and Adam Kosobud, Depart- ment of Psychology, University of Chicago. Portions of the data were previously presented at the annual meeting of the Psychonomic Society, Vancouver, British Columbia, Canada, Novem- ber 2003. This research was supported in part by National Science Foun- dation Grants SBE9704764 and BCS0116293 and by National Science Foundation predoctoral fellowship award DGE-0202337 to Matthew R. Longo. We express our appreciation to Aaron Kozbelt, Stephen Makin, and Sean Duffy for their assistance in creating the stimuli and to Jean Decety and Marcel Brass for their comments on an earlier version of this article. Correspondence concerning this article should be addressed to Bennett I. Bertenthal, Department of Psychology, University of Chicago, 5848 South University Avenue, Chicago, IL 60637. E-mail: bertenthal@uchicago.edu Journal of Experimental Psychology: Copyright 2006 by the American Psychological Association Human Perception and Performance 2006, Vol. 32, No. 2, 210 –225 0096-1523/06/$12.00 DOI: 10.1037/0096-1523.32.2.210 210