The role of mirror neurons in speech and language processing

The discovery of mirror neurons in the macaque frontal cortex (di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti, 1992; Gallese, Fadiga, Fogassi, & Rizzolatti, 1996; Rizzolatti & Arbib, 1998) has sparked renewed interest in the role of the motor system in receptive language processes. This interest has developed primarily around two logically independent, but sometimes conflated, ideas. One is that motor systems involved in speech production are critically involved in perceiving speech sounds (D'Ausilio et al., 2009; Meister, Wilson, Deblieck, Wu, & Iacoboni, 2007; Wilson, Saygin, Sereno, & Iacoboni, 2004), an idea that is clearly related to the motor theory of speech perception (A. M. Liberman, Cooper, Shankweiler, & Studdert-Kennedy, 1967; A.M. Liberman & Mattingly, 1985). The other is that the meaning of action-related words are coded, at least in part, in motor regions that control the execution of those actions (e.g., Hauk, Johnsrude, & Pulvermuller, 2004; Wernicke, 1874/1969). These are independent hypotheses in that one concerns the neural basis of perceiving the phonological form of speech sounds while the other concerns the neural basis of a different level of processing/representation, namely the semantics of a word. Thus, the proposals need to be evaluated independently; evidence for or against one idea does not constitute evidence for or against the other. With this in mind, I would like to introduce this special issue of Brain and Language, which brings together seven original papers presenting theoretical and empirical arguments regarding the role of the motor system in these two domains of language processing. Before introducing the papers, however, it is worth laying out some boundary conditions for evaluating the evidence and claims.