Hurley's shared circuits model (SCM) provides a framework for investigating the role of emulation and imitation in social cognition. The SCM builds on two recent developments in cognitive neuroscience: Grush's (2004) notion of an emulator (originating from motor control theory) and the discovery of mirror and canonical neurons in monkeys. The target article specifically concentrates on the role of shared circuits in imitation, deliberation, and mindreading. However, it says little about their role in language and communication, which presumably underpin many of the cognitive abilities that Hurley focuses on.
Section 2.3.1 of the target article discusses various hypotheses about how imitation might support language. For example, Hurley argues that the “flexible articulated relations between means and ends in imitative learning could be an evolutionary precursor of arbitrary relations between symbols and referents” (para. 2) and that “mirror systems provide a common code for actions of self and other, and thus for language production and perception” (para. 3). Finally, she suggests that the “flexible recombinant structure of ends and means in imitation may be a precursor of recombinant grammatical structure in language” (para. 4).
However, section 3 contains surprisingly little about the relationship between the SCM (and its various layers) and language processing. In fact, it is only when discussing layer 5 (the full-blown model) that language is considered at all. This is in relation to how imitative learning together with learned manipulation of external symbols could support the rich structure of language. Hurley also speculates that language could assist layer 5 circuits in taking input off-line, thereby allowing for more advanced mindreading (e.g., in multi-person strategic deliberation).
By contrast, we suggest that lower layers of the SCM may play a crucial role in language processing, in particular during interactive dialogue, which is the most basic setting for linguistic communication. Notice that some of the strongest evidence for perception priming action is from the language domain. For example, there are now a number of demonstrations of the priming of articulators during speech perception using transcranial magnetic stimulation (TMS) and electromyography (EMG) (Fadiga et al. Reference Fadiga, Craighero, Buccino and Rizzolatti2002; Watkins et al. Reference Watkins, Strafella and Paus2003). We have argued that, during dialogue, interlocutors tend to align their mental states at many levels, and that such alignment is largely a result of priming (Pickering & Garrod Reference Pickering and Garrod2004). Indeed, successful communication appears to occur when interlocutors align their models of the situation under discussion. So it would be surprising if the “shared circuits” underlying imitation and mindreading did not also play an important role in this process. In fact, good evidence suggests that alignment of the situation model is supported by rapid and largely automatic alignment at many linguistic levels, such as sound (e.g., Pardo Reference Pardo2006), syntax (Branigan et al. Reference Branigan, Pickering and Cleland2000), and meaning of expressions (Garrod & Anderson Reference Garrod and Anderson1987).
Such linguistic priming would arise at layer 3 of the SCM, just as it does for the chameleon effect (Chartrand & Bargh Reference Chartrand and Bargh1999). Hurley notes “the intimate relationship between the sharing of circuits for self and other and for action and perception: Layer 3's shared informational dynamics for intersubjectivity presupposes layer 2's shared informational dynamics for perception and action” (sect. 3.3, para. 3). We argue that just such a relationship holds between shared circuits for linguistic representations in communicators and shared informational dynamics for language production and comprehension (Garrod & Pickering Reference Garrod and Pickering2004). In other words, covert and overt imitation (i.e., imitative production) at various linguistic levels promotes alignment or intersubjectivity between linguistic representations at those levels.
It is not only in relation to imitation that dialogue processing involves shared circuits. There is increasing evidence that language comprehension like action observation may use production-based (i.e., action based) emulation. In particular, we have argued that comprehension uses predictions based on simultaneous involvement of components of the language production system in the form of a Grush-style emulator (Pickering & Garrod Reference Pickering and Garrod2007). Such an emulator uses the production system to make predictions (at various linguistic levels) about the input to the comprehension system and runs those predictions in real time. In this way, the system facilitates rapid interpretation and is robust in dealing with ambiguous or noisy language input. At the same time, by priming the production system, the emulator facilitates the rapid switching between comprehension and production during dialogue. Although this production-based emulator is used for comprehending speech, it is built out of exactly the same action-perception components as used in layer 3 of the SCM.
Incorporating control systems into shared circuits for social cognition is a welcome theoretical development. Here we have argued that such shared circuits can also be used to explain how interlocutors align their linguistic representations during dialogue, which ultimately supports successful communication. Indeed, communication is about sharing (with the Latin communicare meaning “to share” or “to make common”), so it should come as no surprise that linguistic communication depends upon shared circuits.
