The overall goal of this target article is to demonstrate a mechanism for an embodied cognition. The particular vehicle is a much-studied, but still widely debated phenomenon seen in 7–12 month-old-infants. In Piaget's classic “A-not-B error,” infants who have successfully uncovered a toy at location “A” continue to reach to that location even after they watch the toy hidden in a nearby location “B.” Here, we question the traditional explanations of the error as an indicator of infants' concepts of objects or other static mental structures. Instead, we demonstrate that the A-not-B error and its previously puzzling contextual variations can be understood by the coupled dynamics of the ordinary processes of goal-directed actions: looking, planning, reaching, and remembering. We offer a formal dynamic theory and model based on cognitive embodiment that both simulates the known A-not-B effects and offers novel predictions that match new experimental results. The demonstration supports an embodied view by casting the mental events involved in perception, planning, deciding, and remembering in the same analogic dynamic language as that used to describe bodily movement, so that they may be continuously meshed. We maintain that this mesh is a pre-eminently cognitive act of “knowing” not only in infancy but also in everyday activities throughout the life span.

Although the dynamic field model predicts infants' perseverative behavior in the context of the A-not-B manual search task, it does not account for infant perseveration in other contexts. An alternative cognitive capacity explanation for perseveration is more parsimonious. It accounts for the graded nature of perseverative responses and perseveration in different contexts.

In the dynamic field model, parametric variations of the same general processes predict how infants reach for a goal. Animal learning investigators argue that locating a goal is the product of qualitatively different mechanisms (response learning and place learning) Response versus place learning experiments suggest limitations to the dynamic field model hut where those limitations begin or end is unclear.

I suggest that neurophysiological data, usually interpreted in cognitivist terms, is actually more supportive of dynamic frameworks such as that of Thelen et al. I outline a model of embodied action used to interpret neural data from frontal and parietal cortex, and suggest that it bears strong similarity to the framework described in the target article.

Thelen et al.'s model of A-not-B performance is based on behavioral observations obtained with a paradigm markedly different from A-not-B. Central components of the model are not central to A-not-B performance. All data presented fit a simpler model, which specifies that the key abilities for success on A-not-B are working memory and inhibition. Intention and action can be dissociated in infants and adults.

Although the model proposed by Thelen and co-authors provides a detailed explanation for the processes underlying reaching, many aspects of it are highly speculative. One of the reasons for this is our lack of knowledge about transformation of a hand movement plan into joint movements. The leading joint hypothesis (LJH) allows us to partially fill in this gap. The LJH offers a possible explanation for the formation of movement and how it may be represented in memory. Our explanation converges with the dynamic model described in the target article.

Thelen et al. have a strong case for linking behavior with mind through nonrepresentational dynamics. Their case linking mind with brain is less compelling. Modified avenues are proposed for further exploration: greater emphasis on the dynamics of perception; use of chaotic instead of deterministic dynamics with noise; and use of intentionality instead of motivation, taking advantage of its creative dynamics to model genesis of goal-directed behaviors.

An embodied movement-planning field cannot account for behavior and cognition more abstract than that of reaching. Instead, we propose an affordance field, and we sketch how it could enhance the analysis of the A-not-B error, underlie cognition, and serve as a base for language. Admittedly, a dynamic systems account of an affordance field awaits significant further development.

A-not-B behavior in various mammals and birds suggests it has been selected for during evolution. One scenario is that displacement to B of one food item from a trove at A should not distract the forager. Piagetian stage V experiments may not test for object permanence, but rather for the more abstract notion that physical objects can be unique.

Top-down dynamical models of cognitive processes, such as the one presented by Thelen et al., are important pieces in understanding the development of cognitive abilities in humans and biological organisms. Unlike standard symbolic computational approaches to cognition, such dynamical models offer the hope that they can be connected with more bottom-up, neurologically inspired dynamical models to provide a complete view of cognition at all levels. We raise some questions about the details of their simulation and about potential limitations of top-down dynamical models.

Errors and episodes of “freezing” seen during mirror writing by adults can be incorporated into the model suggested in Thelen et al.'s target article This requires assigning an important role to internal inverse models stored in memory. The strongly anti-dualism position of Thelen et al.'s leaves little room for the Bernsteinian notion of activity.

Some dynamic systems approaches posit discontinuous changes, even universal stages, in development. Conversely, Thelen and colleagues see development as gradual because it relies on real-time interactions among many components. Yet their new model hinges on one parameter, neural cooperativity, that should change discontinuously because it engenders new skills that catalyze neural connectivity. In fact, research on cortical connectivity finds development to be discontinuous, and possibly stage-like, based on experience-dependent and experience-independent factors.

Thelen et al. not only offer an important new theoretical account of the Stage 4 object permanence error but provide the foundation of a new theory of cognitive development that is grounded in action. The success of dynamic field theory as a more general account of cognitive functioning, however, will depend on the degree to which it can model more generative capacities that are not limited to simple choice situations. Imitation and problem solving are suggested as two capacities that might be productively modeled within their approach.

The dynamic systems approach simulates a wide range of effects and generates novel predictions, but it fails to explain age-related behavioral changes in psychological terms. We argue that the roles of conscious control and explicit knowledge must be addressed in any model of A-not-B performance, and a fortiori, in any model of goal-directed action.

A mature science strives to provide causal explanations of observed phenomena rather than focusing on taxonomic descriptions of data. A field theory model is a step towards providing a truly scientific account of development. However, the model is under-constrained in that it ignores the boundary conditions defined by the physical constraints imposed by the infant's developing brain and body.

The proposed model is put forward as a template for the dynamical systems approach to embodied cognition. In order to extend this view to cognitive processing in general, however, two limitations must be overcome. First, it must be demonstrated that sensorimotor coordination of the type evident in the A-not-B error is typical of other aspects of cognition. Second, the explanatory utility of dynamical systems models must be clarified.

This commentary is a brief reflection on the relationship between the embodied cognition analysis and a Piagetian theoretical position. In particular, the place of A-not-B in the larger Piagetian framework and the importance of the concept of mental representation, in contrast with perceptual understanding, are noted.

The mathematical approach to such essentially biological phenomena as perseverative reaching is most welcome. To extend these results and make them more accurate, levels of analysis and neural centers should he distinguished. The navigational nature of sensorimotor control should be characterized more clearly, including the continuous dynamics of neural processes hut not limited to it. In particular, discrete conditions should be formalized mathematically as part of the biological process.

Thelen and her colleagues' model overemphasizes the role of action in cognitive development. Recent research has shown that infants do not have to be trained to reach for a hidden object. By 7.5 months of age, infants can recall the location of a hidden object with no practice trials. Thelen at al.'s goal to design a parsimonious account of A-not-B behaviors was successful, but at the expense of focusing primarily on implicit and ignoring explicit memory.

The procedures used to ensure reliable occurrences of the A-not-B error distort and miss essential features of Piaget's original observations. A model that meshes a mental event, highly restricted by testing procedures, to the dynamics of bodily movement is of limited value. To embody more than just perseverative reaching, the formal model must incorporate Piaget's essential features.