To become language users, infants must embrace the integrality of speech perception and production. That they do so, and quite rapidly, is implied by the native-language attunement they achieve in each domain by 6-12 months. Yet research has most often addressed one or the other domain, rarely how they interrelate. Moreover, mainstream assumptions that perception relies on patterns whereas production involves patterns entail that the infant would have to translate incommensurable information to grasp the perception-production relationship. We posit the more parsimonious view that both domains depend on commensurate information. Our proposed framework combines principles of the Perceptual Assimilation Model (PAM) and Articulatory Phonology (AP). According to PAM, infants attune to articulatory information in native speech and detect similarities of nonnative phones to native articulatory patterns. The AP premise that gestures of the speech organs are the basic elements of phonology offers articulatory similarity metrics while satisfying the requirement that phonological information be discrete and contrastive: (a) distinct articulatory organs produce vocal tract constrictions and (b) phonological contrasts recruit different articulators and/or constrictions of a given articulator that differ in degree or location. Various lines of research suggest young children perceive articulatory information, which guides their productions: discrimination of between- versus within-organ contrasts, simulations of attunement to language-specific articulatory distributions, multimodal speech perception, oral/vocal imitation, and perceptual effects of articulator activation or suppression. We conclude that articulatory gesture information serves as the foundation for developmental integrality of speech perception and production.

One of the hallmarks of any flexible system of perception and motor control is the ability to adjust to changes induced by dialect, development, fatigue, disease, or aging. Phonetic categories are an essential component of language that enables listeners and speakers to communicate effectively. Four studies are reviewed that illustrate how adults and infants adjust their phonetic categories rapidly and efficiently to maintain a tight coupling between speech perception and speech production. Although this process of adaptive plasticity takes place at the level of phonetic categories, it is also constrained by the lexicon. Words that share similar sounds or similar vocal-articulatory gestures impede the process of adaptation.

Unlike affordances involving stationary objects, affordances involving moving objects change over time. This means that actions must be tightly linked to decisions, making perceiving and acting on affordances involving moving objects challenging for children and adults alike. Here, we overview our program of research on how children and adults perceive and act on moving objects in the context of bicycling across roads in an immersive virtual environment. This work shows that although children attempt to adjust their actions to fit their risky decisions, they do not fully adjust their decisions to fit their action capabilities. This mismatch between child cyclists' decisions and actions may be a risk factor for car-bicycle collisions in late childhood and early adolescence.

The focus of this paper is on characterizing the physical movement forms (e.g., walk, crawl, roll, etc.) that can be used to actualize abstract, functionally-specified behavioral goals (e.g., locomotion). Emphasis is placed on how such forms are distinguished from one another, in part, by the set of topological patterns of physical contact between agent and environment (i.e., the set of associated with each form) and the transitions among these patterns displayed over the course of performance (i.e., the form's ). Crucial in this regard is the creation and dissolution of loops in these graphs, which can be related to the distinction between open and closed kinematic chains. Formal similarities are described within the theoretical framework of between physically-closed kinematic chains (physical loops) that are created during various movement forms and functionally-closed kinematic chains (functional loops) that are associated with task-space control of end-effectors; it is argued that both types of loop must be flexibly incorporated into the coordinative structures that govern skilled action. Final speculation is focused on the role of graphs and their dynamics, not only in processes of coordination and control for individual agents, but also in processes of inter-agent coordination and the coupling of agents with (non-sentient) environmental objects.

Tools are a universal feature of human culture. While most past research on tool use has focused on its cognitive underpinnings, in the present article we adopt a perception-action approach to understand how tool use emerges in early development. In this context, we review our work on infant object banging and how it may serve as a motor substrate for percussive tool use. Our results suggest that infants use banging to act on environmental surfaces selectively. Additionally, with increasing age, banging becomes more controlled and manifests many characteristics associated with skilled hammering. Taken together, the results suggest that there is much to be gained from considering the emergence of tool use as an ongoing process of perceptuomotor adaptation to handheld objects.

Language use has a public face that is as important to study as the private faces under intensive psycholinguistic study. In the domain of phonology, public use of speech must meet an interpersonal "parity" constraint if it is to serve to communicate. That is, spoken language forms must reliably be identified by listeners. To that end, language forms are embodied, at the lowest level of description, as phonetic gestures of the vocal tract that lawfully structure informational media such as air and light. Over time, under the parity constraint, sound inventories emerge over communicative exchanges that have the property of sufficient identifiability.Communicative activities involve more than vocal tract actions. Talkers gesture and use facial expressions and eye gaze to communicate. Listeners embody their language understandings, exhibiting dispositions to behave in ways related to language understanding. Moreover, linguistic interchanges are embedded in the larger context of language use. Talkers recruit the environment in their communicative activities, for example, in using deictic points. Moreover, in using language as a "coordination device," interlocutors mutually entrain.

Several conjectures by A. S. Iberall on life and mind are used as a backdrop to sketch a theory of mental activity that respects both the contents of thought and the dynamics of thinking. The dynamics, in this case, refers fundamentally to animated, meaningfully coupled self-organizing processes (coordination dynamics) and exhibit multistability, switching, and, because of symmetry breaking, metastability. The interplay of 2 simultaneously acting forces underlies the metastable mind: the tendency for the coordinating elements to couple together (integration) and the tendency for the elements to express their individual autonomy (segregation). Metrics for metastability are introduced that enable these cooperative and competitive tendencies to be quantified. Whereas bistability is the basis for polarized, either/or thinking, the metastable régime-which contains neither stable nor unstable states, no states at all, in fact-gives rise to a far more fluid, complementary mode of operation in which it is possible for apparent contraries to coexist in the mind at the same time.

Four experiments examined the nature of multisensory speech information. In Experiment 1, participants were asked to match heard voices with dynamic visual-alone video clips of speakers' articulating faces. This cross-modal matching task was used to examine whether vocal source matching can be accomplished across sensory modalities. The results showed that observers could match speaking faces and voices, indicating that information about the speaker was available for cross-modal comparisons. In a series of follow-up experiments, several stimulus manipulations were used to determine some of the critical acoustic and optic patterns necessary for specifying cross-modal source information. The results showed that cross-modal source information was not available in static visual displays of faces and was not contingent on a prominent acoustic cue to vocal identity (f0). Furthermore, cross-modal matching was not possible when the acoustic signal was temporally reversed.

In introducing the articles of this special issue on language, which grew out of the conference "Grounding Language in Perception and (Inter) Action," we take the opportunity to reflect on fundamental aspects of speaking and listening to others that are often overlooked. The act of conversing is marked by context sensitivity, interdependency, impredicativity, irreversibility, and responsibility, among other things. Language entails real work: it involves real movements in physical, social, and moral orders that are distributed across a wide array of spatial-temporal scales (e.g., evolutionary, historical); yet there is a dimension of play "at work" as well. These workings of language are embedded and embodied in distributed ways that reveal the fundamentally social, public nature of the activity. It is a form of coaction that is dialogical and dynamic in ways that may point to deeper understandings of what it means for perception to be direct and for action to be specific. Language locates us.

How children pick up a tool reveals their ability to plan an action with the end goal in mind. When presented with a spoon whose handle points away from their dominant hand, children between infancy and 8 years of age progress from using an awkward ulnar grip that causes food to spill from the spoon to consistently using a radial grip. At 4 years of age children's grip strategies are highly variable, including the awkward grips of infancy and use of the non-dominant hand, but they also employ adult-like grips never seen in infancy. By 8 years of age the infantile ulnar grip has completely disappeared and is replaced by more mature and effective grips that indicates better planning for the end goal.

We propose a new way to describe affordances for action. Previous characterizations of affordances treat action possibilities as binary categories-either possible or impossible-separated by a critical point. Here, we show that affordances are probabilistic functions, thus accounting for variability in motor performance. By measuring an affordance function, researchers can describe the likelihood of success for every unit of the environment. We demonstrate how to fit an affordance function to performance data using established psychophysical procedures and illustrate how the threshold and variability parameters describe different possibilities for action. Finally, we discuss the implications of probabilistic affordances for development, perception, and decision-making.

Carol Fowler has had a tremendous impact on the field of speech perception, in part by having people disagree with her. The disagreements arise, as they often do, from two incompatible sources: Her positions are often misunderstood and thus "disagreed" with only on the surface, and her positions are rejected because they challenge deeply held, intuitively appealing positions, without being shown to be wrong. The misunderstandings center largely on the assertion that perception is "direct." This is often taken to mean that we have access to the speaker's vocal tract by some means other than the (largely acoustic) speech signal, when, in fact, it asserts that the signal is sufficient to directly specify that production. It is unclear why this misunderstanding persists; while there are still issues to be resolved in this regard, the stance is clear. The challenge to "acoustic" theories of speech perception remains, and thus direct perception is still controversial, as it seems that acoustic theories are held by a majority of researchers. Decades' worth of evidence showing the lack of usefulness of purely acoustic properties and the coherence gained by a production perspective have not changed this situation. Some attempts at combining the two perspectives have emerged, but they largely miss the Gibsonian challenge that Fowler has espoused: Perception of speech is direct. It looks as though it will take some further decades of research and discussion to fully explore her position.

When a listener can also see a talker, audible and visible properties are ineluctably combined, perceptually. This perceptual disposition to audiovisual integration has received widely ranging explanations. At one extreme, accounts have likened perception to a blind listener and a deaf viewer combined within a single skin, resolving discrepancies in identification by each modality. At the other extreme, perception has been described as necessarily and automatically synesthetic. Useful descriptive and explanatory evidence was provided in a study of auditory-haptic presentation by Fowler and Dekle (1991), showing that neither familiarity nor congruence is required for perceptual integration to occur across modalities. Instead, the notion of conjoint lawful specification was proposed as a governing constraint. This principle treats sensory activity as proximal sampling of the properties of distal objects and events, and this essay notes that its corollaries offer a broadly applicable guide in contemporary investigations of perception.

How one behaves after interacting with a friend may not be the same as before the interaction. The present study investigated which spontaneous coordination patterns formed between two persons and whether a remnant of the interaction remained ("social memory"). Pairs of people sat face-to-face and continuously flexed index fingers while vision between partners was manipulated to allow or prevent information exchange. Trials consisted of three successive twenty-second intervals: without vision, with vision, and again without vision. Steady, transient, or absent phase coupling was observed during vision. In support of social memory, participants tended to remain near each other's movement frequency after the interaction ended. Furthermore, the greater the stability of interpersonal coordination, the more similar partners' post-interactional frequencies became. Proposing that social memory resulted from prior frequency adaptation, a model based on Haken-Kelso-Bunz oscillators reproduced the experimental findings, even for patterns observed on individual trials. Parametric manipulations revealed multiple routes to social memory through the interplay of adaptation and other model parameters. The experimental results, model, and interpretation motivate potential future research and therapeutic applications.

Surgical design in personalized medicine is often based on native anatomy, which may not accurately reflect the interaction between native musculoskeletal tissues and biomechanical artifacts. To overcome this problem, researchers have developed alternative methods based on affordance-based design. The design process can be viewed in terms of action possibilities provided by the (biological) environment. Here, we use the affordance-based approach to address possibilities for action offered by biomechanical artifacts. In anterior crucial ligament (ACL) reconstruction, the design goal is to avoid ligament impingement while optimizing the placement of the tibial tunnel. Although in the current rationale for tibial tunnel placement roof impingement is minimized to avoid a affordance, we show that tibial tunnel placement can rather aim to constrain the target bounds with respect to a affordance. We describe the steps for identifying the measurable invariants and provide a mathematical framework for the surgery affordances within the knee.