Currently, production and comprehension are regarded as quite distinct in accounts of language processing. In rejecting this dichotomy, we instead assert that producing and understanding are interwoven, and that this interweaving is what enables people to predict themselves and each other. We start by noting that production and comprehension are forms of action and action perception. We then consider the evidence for interweaving in action, action perception, and joint action, and explain such evidence in terms of prediction. Specifically, we assume that actors construct forward models of their actions before they execute those actions, and that perceivers of others' actions covertly imitate those actions, then construct forward models of those actions. We use these accounts of action, action perception, and joint action to develop accounts of production, comprehension, and interactive language. Importantly, they incorporate well-defined levels of linguistic representation (such as semantics, syntax, and phonology). We show (a) how speakers and comprehenders use covert imitation and forward modeling to make predictions at these levels of representation, (b) how they interweave production and comprehension processes, and (c) how they use these predictions to monitor the upcoming utterances. We show how these accounts explain a range of behavioral and neuroscientific data on language processing and discuss some of the implications of our proposal.

Knowledge of the complexity of human communication comes from three main sources – (i) studies of the linguistics and neuropsychology of dysfunction after brain injury; (ii) studies of the development of social communication in infancy, and its dysfunction in developmental psychopathologies; and (iii) the evolutionary history of human communicative interaction. Together, these suggest the need for a broad, integrated theory of communication of which language forms a small but critical component.

Pickering & Garrod (P&G) put forward the interesting idea that language production relies on forward modeling operating at multiple processing levels. The evidence currently available to substantiate this idea mostly concerns sensorimotor processes and not more abstract linguistic levels (e.g., syntax, semantics, phonology). The predictions that follow from the claim seem too general, in their current form, to guide specific empirical tests.

The project of coordinating perception, comprehension, and motor control is an exciting one, but I found it hard to follow some of Pickering & Garrod's (P&G's) arguments as presented. Consequently, my comment is not so much a disagreement with P&G but a query about the logic of forward models: It is not clear how they are supposed to work, nor why they are needed in this (or many other) contexts, and toward that end I present an alternative idea.

Both children and adults predict the content of upcoming language, suggesting that prediction is useful for learning as well as processing. We present an alternative model which can explain prediction behaviour as a by-product of language learning. We suggest that a consideration of language acquisition places important constraints on Pickering & Garrod's (P&G's) theory.

We encourage Pickering & Garrod (P&G) to implement this promising theory in a computational model. The proposed theory crucially relies on having an efficient and reliable mechanism for early intention recognition. Furthermore, the generation of impoverished predictions is incompatible with a number of key phenomena that motivated P&G's theory. Explaining these phenomena requires fully specified perceptual predictions in both comprehension and production.

Interactive theories of lexical retrieval in language production assume that activation cascades from earlier to later processing levels, and feeds back in the reverse direction. This commentary invites Pickering & Garrod (P&G) to consider whether cascading and feedback can be seen as a form of forwarding modeling within a hierarchical production system.

With a focus on receptive language, we examine the neurobiological evidence for the interdependence of receptive and expressive language processes. While we agree that there is compelling evidence for such interdependence, we suggest that Pickering & Garrod's (P&G's) account would be enhanced by considering more-specific situations in which their model does, and does not, apply.

Given that Pickering & Garrod's (P&G's) account integrates language production and comprehension, it is reasonable to ask whether it is compatible with embodied cognition. I argue that its dependence on rich intermediate representations of linguistic structure excludes embodiment. Two options are available to supporters of embodied cognition: They can adopt a more liberal notion of embodiment or they can attempt to replace these intermediate representations with robustly embodied ones. Both of these options face challenges.

In examining the utility of the action view advanced in the Pickering & Garrod (P&G) target article, I first consider its contribution to the analysis of language vis-à-vis earlier language-as-action approaches. Second, I assess the relation between coordinated joint action, which serves as a blueprint for dialogue coordination, and the experience of shared reality, a key concomitant and product of interpersonal communication.

Language processing changes with the knowledge and use of two languages. The advantage of being bilingual comes at the expense of increased processing demands and processing costs. I suggest considering bilingual complexity including these demands and costs. The proposed model claims effortless monolingual processing. By integrating individual and situational variability, the model would lose its idealistic touch, even for monolinguals.

Embedding theories of language production and comprehension in theories of action-perception is realistic and highlights that production and comprehension processes are interleaved. However, layers of internal models that repeatedly predict future linguistic actions and perceptions are implausible. I sketch an ecological alternative whereby perceiver/actors are modeled as dynamical systems coupled to one another and to the environment.

At the core of Pickering & Garrod's (P&G's) theory is a monitor that uses forward models. I argue that this account is challenged by neuropsychological findings and visual world eye-tracking data and that it has two conceptual problems. I propose that conflict monitoring avoids these issues and should be considered a promising alternative to perceptual loop and forward modeling theories.

There is little doubt that predictive coding is an important mechanism in language processing–indeed, in information processing generally. However, it is less clear whether the action system is the source of such predictions during perception. Here I summarize the computational problem with motor prediction for perceptual processes and argue instead for a dual-stream model of predictive coding.

We present empirical evidence from dialogue that challenges some of the key assumptions in the Pickering & Garrod (P&G) model of speaker-hearer coordination in dialogue. The P&G model also invokes an unnecessarily complex set of mechanisms. We show that a computational implementation, currently in development and based on a simpler model, can account for more of this type of dialogue data.

We welcome the proposal to use forward models to understand predictive processes in language processing. However, Pickering & Garrod (P&G) miss the opportunity to provide a strong framework for future work. Forward models need to be pursued in the context of learning. This naturally leads to questions about what prediction error these models aim to minimize.

Although the target article emphasizes the important role of prediction in language use, prediction may well also play a key role in the initial formation of linguistic representations, that is, in language development. We outline the role of prediction in three relevant language-learning domains: transitional probabilities, statistical preemption, and construction learning.

Although applauding Pickering & Garrod's (P&G's) attempt to ground language use in the ideomotor perception-action link, which provides an “infrastructure” of embodied social interaction, we suggest that it needs to be complemented by an additional control mechanism that modulates its operation in the service of the language users' communicative intentions. Implications for intergroup relationships and intercultural communication are discussed.

Pickering & Garrod's (P&G's) framework assumes an efference copy based on the interlocutor's intentions. Yet, elaborate attribution of intentions may not always be necessary for online prediction. Instead, contextual cues such as speaker gaze can provide similar information with a lower demand on processing resources.

The integration of language production and comprehension processes may be more specific in terms of developmental timing than Pickering & Garrod (P&G) discuss in their target article. Developmental studies do reveal links between production and comprehension, but also demonstrate that the integration of these skills changes over time. Production-comprehension links occur within specific language skills and specific time windows.