We comment that covariances between brain divisions may be constraining or facilitating, depending on what is being selected, and that modern quantitative genetic methods provide the tools to discover and manipulate the genetic networks that give rise to the covariances described in the target article.

Bloom masterfully captures the state-of-the-art in the study of lexical acquisition. He also exposes the extent of our ignorance about the learning of names for non-observables. HCLMW adopts an innatist position without adopting modularity of mind; however, it seems likely that modularity is needed to bridge the gap between object names and the rest of the lexicon.

The HIT framework accepts a number of assumptions that are widely held as plausible or even well established in the literature on category-specific agnosia. We point out that a number of these elementary conjectures, now almost taken for granted, have received little in the way of convincing empirical support.

Shepard's approach is regarded as an attempt to rescue, within an evolutionary perspective, an empiricist theory of mind. Contrary to this, I argue that the structure of perceptual representations is essentially co-determined by internal aspects and cannot be understood if we confine our attention to the physical side of perception, however appropriately we have chosen our vocabulary for describing the external world. Furthermore, I argue that Kubovy and Epstein's “more modest interpretation” of Shepard's ideas on motion perception is based on unjustified assumptions. [Kubovy & Epstein; Shepard]

In dynamical systems models feedforward is needed to guide planning and to process unknown and unpredictable events. Feedforward could help Theory of Event Coding (TEC) integrate control processes and could model human performance in action planning in a more flexible and powerful way.

Cowan's revisiting of the magic number is very timely and the case he makes for a more moderate number than seven is persuasive. It is also appropriate to frame his case within a theoretical context, since this will influence what evidence to include and how to interpret it. He presents his model however, as a contrast to the working memory model of Baddeley (1986). I suggest that this reflects a misinterpretation of our model resulting in a danger of focusing attention on pseudo-problems rather than genuine disparities between his approach and my own.

The human brain does not use more energy than the smaller brains of animals of comparable corporal weight. Uniquely, human functions localized largely in parts of the human brain that show greatest size increase over other animals may be mediated primarily by nonsynaptic neurotransmission, with reduced energy cost per kilogram of brain. This may affect the energetic constraints on evolution.

Most current theories of category-specific semantic deficits appeal to the role of sensory and functional knowledge types in explaining patients' impairments. We discuss why this binary classification is inadequate, point to a more detailed knowledge type taxonomy, and suggest how it may provide insight into the relationships between category-specific semantic deficits and impairments of specific aspects of knowledge.

The probabilistic analysis of functional questions is maturing into a rigorous and coherent research paradigm that may unify the cognitive sciences, from the study of single neurons in the brain to the study of high level cognitive processes and distributed cognition. Endless debates about undecidable structural issues (modularity vs. interactivity, serial vs. parallel processing, iconic vs. propositional representations, symbolic vs. connectionist models) may be put aside in favor of a rigorous understanding of the problems solved by organisms in their natural environments. [Shepard; Tenenbaum & Griffiths]

The Theory of Event Coding (TEC) is a new framework for understanding interactions between perception and action. We are concerned that the theory is underspecified, showing that it can easily be used to make exactly opposite predictions. Precise specification of the time course of activation and binding is needed to make the theory useful for understanding the perception-action interface.

The complex relationship between attention and STM forms a core issue in the study of human cognition, and Cowan's target article attempts, quite successfully, to elucidate an important part of this relationship. However, while I agree that aspects of STM performance may reflect the action mechanisms that we normally consider to subserve “attention” I shall argue here that attention is not subject to a fixed four-object capacity limit as Cowan suggests. Rather, performance in attention tasks as well as STM may be best accounted for in terms of decay and interference.

Bloom's eloquent and comprehensive treatment of early word learning holds that social intention is foundational for language development. While we generally support his thesis, we call into question two of his proposals: (1) that attention to social information in the environment implies social intent, and (2) that infants are sensitive to social intent at the very beginnings of word learning.

The opposition set up between co-ordinated and mosaic brain evolution distracts from the fact that the two go hand-in-hand. Here and elsewhere (Barton & Harvey 2000), I show that the patterns of co- ordinated evolutionary change among brain structures fit a mosaic evolution model. The concept of overarching developmental constraints is unnecessary and is not supported by the data.

The purpose of the commentary is not to contradict HIT but rather to question whether its increase in predictive power outweighs the decrease in parsimony. For the refutable aspects of HIT, a simpler model for naming appears to achieve as much. Both models better fit the facts concerning naming performance than describe category-specificity.

Acquisition of word meanings, or vocabulary, reflects general mental ability (psychometric g) more than than do most abilities measured in test batteries. Among diverse subtests, vocabulary is especially high on indices of genetic influences. Bloom's exposition of the psychological complexities of understanding words, involving the primacy of concepts, the theory of mind, and other processes, explains vocabulary's predominant g saturation.

The Theory of Event Coding (TEC) provides a preliminary account of the interaction between perception and action, which is consistent with several recent findings in the area of motor control. Significant issues require integration and elaboration, however; particularly, distractor interference, automatic motor corrections, internal models of action, and neuroanatomical bases for the link between perception and action.

Cowan's experimental techniques cannot constrain subject's recall of presented information to distinct independent chunks in short-term memory (STM). The encoding of associations in long-term memory contaminates recall of pure STM capacity. Even in task environments where the functional independence of chunks is convincingly demonstrated, individuals can increase the storage of independent chunks with deliberate practice – well above the magical number four.

The evidence for a kinematics of the mind is confounded by uncontrolled properties of pictures. Effects of illumination and of picture-plane geometry may underlie some evidence given for a process of mental rotation. Pictured rotation is confounded by picture similarity, gauged by gray-level correlations. An example is given involving the depicted rotation of Shepard-Metzler solids in depth. [Hecht; Kubovy & Epstein; Shepard; Todorovič]

Different hypotheses about the mechanisms underlying working memory lead to different predictions about working memory capacity when information is distributed across the two hemispheres. We present preliminary data suggesting that memory scanning time (a parameter often associated with working memory capacity) varies depending on how information is subdivided across hemispheres. The data are consistent with a distributed model of working memory.

Bloom makes a strong case that word meaning acquisition does not require a dedicated word learning system. This conclusion, however, does not argue against a dedicated language acquisition system for syntax, morphology, and aspects of semantics. Critical questions are raised as to why word meaning should be so different from other aspects of language in the course of acquisition.