We discuss the assumptions put forward by Thelen et al. about motor planning processes. We examine the results of an experiment inspired by the authors' contention that the motor plans of both infants and adults are continuous and graded. We wondered whether adults, in an adapted version of the A-not-B error paradigm, would point between the A and B targets, as in some degraded conditions of pointing (Ghez et al. 1990), or would make A-not-B errors. Unexpectedly, we observed that adults tended to shift the direction of their pointings to B away from A, and did not make any A-not-B errors.

Biological models are useful not only because they can simulate biological behaviors, but because they may shed light on the inner workings of complex biological structures and functions as deduced by top-down and/or bottom-up reasoning. Beyond the stylistic appeal of specific implementation methods, a model should be appraised according to its ability to bring out the underlying organizing and operating principles – which are truly the model's heart and soul.

We show that Stoffregen & Bardy's arguments against the assumption of separately functioning senses have more historical antecedents than they give credit for, and that multimodal functioning – primitive in perceptual and brain development – does not require this assumption. What is needed is evidence that biological organisms are indeed detecting and acting upon information in a multimodal (or global) array.

Shepard's internalization concept is defended against Hecht's criticisms. By ignoring both Shepard's evolutionary perspective and the fact that internalization does not preclude modularization, Hecht advances inconclusive evidence. Developmental research supports Shepard's conclusion that kinematic geometry may be more deeply internalized than physical dynamics. This research also suggests that the internalization concept should be broadened to include representations acquired during ontogeny. [Hecht; Shepard]

Hertwig and Ortmann (H&O) rightly criticize the usage of deception. However, stationary replication may often have no ecological validity. Many economic experiments are not interactive; when they are, there is not much specifically validating H&O's psychological views on script enactment. Incentives in specific market structures may scaffold even zero rational decision-making, but this says very little about individual psychology.

We agree with the authors that an adequate account of the perception-action interface is needed. However, we believe that the answer will not be found in a common representational structure encoding distal events, as the authors propose, but in Gibson's notion of ecological information, which, as we demonstrate, specifies not only perspective but also prospective and retrospective states of affairs.

It appears there is general support amongst the commentaries for the potential usefulness of biorobots as models, with some caveats. These include the issue that not all areas of biology have been addressed by this methodology (and perhaps some cannot be?); and that other methodologies may sometimes be more useful. Which dimensions of biorobotic (or other models) are considered important varies with the goals of the investigator. These goals are also an essential part of the “modelling relationship.”

We argue that mentalistic constructs like the “object concept” are not substitutes for process explanations of cognition, and that it is impossible to prove the existence of such constructs with behavioral tasks. We defend the field theory as an appropriate level for modeling embodiment. Finally, we discuss the model's biological plausibility and its extensions to other tasks and other species.

In advocating an extreme form of specification requiring the abolition of separate senses, Stoffregen & Bardy run the risk of diverting attention from the multisensory integration of perception and action they wish to champion.

Behavioral regularities are open to both representationist (hence internalist) and non-representationist explanations. Shepard improvidently favors internalism, which is burdened with severe conceptual and empirical shortcomings. Hecht and Kubovy & Epstein half-heartedly criticize internalism by tracing it back to “unconscious” metaphors or by replacing it with weak externalism. Explanations of behavioral regularities are better relocated within a radical embodiment approach. [Hecht; Kubovy & Epstein; Shepard]

This response reinforces the major themes of our target article. The impact of key methodological variables should not be taken for granted. Rather, we suggest grounding experimental practices in empirical evidence. If no evidence is available, decisions about design and implementation ought to be subjected to systematic experimentation. In other words, we argue against empirically blind conventions and against methodological choices based on beliefs, habits, or rituals. Our approach will neither inhibit methodological diversity nor constrain experimental creativity. More likely, it will promote both goals.

Miller (1956) summarized evidence that people can remember about seven chunks in short-term memory (STM) tasks. However, that number was meant more as a rough estimate and a rhetorical device than as a real capacity limit. Others have since suggested that there is a more precise capacity limit, but that it is only three to five chunks. The present target article brings together a wide variety of data on capacity limits suggesting that the smaller capacity limit is real. Capacity limits will be useful in analyses of information processing only if the boundary conditions for observing them can be carefully described. Four basic conditions in which chunks can be identified and capacity limits can accordingly be observed are: (1) when information overload limits chunks to individual stimulus items, (2) when other steps are taken specifically to block the recoding of stimulus items into larger chunks, (3) in performance discontinuities caused by the capacity limit, and (4) in various indirect effects of the capacity limit. Under these conditions, rehearsal and long-term memory cannot be used to combine stimulus items into chunks of an unknown size; nor can storage mechanisms that are not capacity-limited, such as sensory memory, allow the capacity-limited storage mechanism to be refilled during recall. A single, central capacity limit averaging about four chunks is implicated along with other, noncapacity-limited sources. The pure STM capacity limit expressed in chunks is distinguished from compound STM limits obtained when the number of separately held chunks is unclear. Reasons why pure capacity estimates fall within a narrow range are discussed and a capacity limit for the focus of attention is proposed.

Normal children learn tens of thousands of words, and do so quickly and efficiently, often in highly impoverished environments. In How Children Learn the Meanings of Words, I argue that word learning is the product of certain cognitive and linguistic abilities that include the ability to acquire concepts, an appreciation of syntactic cues to meaning, and a rich understanding of the mental states of other people. These capacities are powerful, early emerging, and to some extent uniquely human, but they are not special to word learning. This proposal is an alternative to the view that word learning is the result of simple associative learning mechanisms, and it rejects as well the notion that children possess constraints, either innate or learned, that are specifically earmarked for word learning. This theory is extended to account for how children learn names for objects, substances, and abstract entities, pronouns and proper names, verbs, determiners, prepositions, and number words. Several related topics are also discussed, including naïve essentialism, children's understanding of representational art, the nature of numerical and spatial reasoning, and the role of words in the shaping of mental life.

Infants are global perceivers. They detect patterns in stimulation that allow detection of many affordances of the environment. Pick-up of structural patterns across forms of ambient energy awaits maturation of sensory systems and improvements in motor skill, but development proceeds rapidly during the first year. Researchers in perceptual development must devise and refine existing tools to examine infants' abilities.

We review studies on catching that reveal internalization of physics for action control. In catching free-falling balls, an internal model of gravity is used by the brain to time anticipatory muscle activation, modulation of reflex responses, and tuning of limb impedance. An internal model of the expected momentum of the ball at impact is used to scale the amplitude of anticipatory muscle activity. [Barlow; Hecht; Shepard]

This commentary focuses on Hommel et al.'s inferences on action planning. It discusses the relevance of anticipated extrinsic movement effects for action control, the problems of a feature-based representation of actions, and the necessity of the acquisition of conditional movement-effect associations.

The empirical data do not unequivocally support a consistent fixed capacity of four chunks. We propose an alternative account whereby capacity is limited by the precision of specifying the temporal and spatial context in which items appear, that similar psychophysical constraints limit number estimation, and that short term memory (STM) is continuous with long term memory (LTM).

While Tenenbaum and Griffiths impressively consolidate and extend Shepard's research in the areas of stimulus representation and generalization, there is a need for complexity measures to be developed to control the flexibility of their “hypothesis space” approach to representation. It may also be possible to extend their concept learning model to consider the fundamental issue of representational adaptation. [Tenenbaum & Griffiths]

We discuss the relation of the Theory of Event Coding (TEC) to a computational model of expert perception, CHREST, based on the chunking theory. TEC's status as a verbal theory leaves several questions unanswerable, such as the precise nature of internal representations used, or the degree of learning required to obtain a particular level of competence: CHREST may help answer such questions.

Category-specific impairments of object recognition and naming are among the most intriguing disorders in neuropsychology, affecting the retrieval of knowledge about either living or nonliving things. They can give us insight into the nature of our representations of objects: Have we evolved different neural systems for recognizing different categories of object? What kinds of knowledge are important for recognizing particular objects? How does visual similarity within a category influence object recognition and representation? What is the nature of our semantic knowledge about different objects? We review the evidence on category-specific impairments, arguing that deficits even for one class of object (e.g., living things) cannot be accounted for in terms of a single information processing disorder across all patients; problems arise at contrasting loci in different patients. The same apparent pattern of impairment can be produced by damage to different loci. According to a new processing framework for object recognition and naming, the hierarchical interactive theory (HIT), we have a hierarchy of highly interactive stored representations. HIT explains the variety of patients in terms of (1) lesions at different levels of processing and (2) different forms of stored knowledge used both for particular tasks and for particular categories of object.