Our concerns fall into three areas: (1) Barsalou fails to make clear what simulators are (vs. what they do); (2) activation of perceptual areas of the brain during thought does not distinguish between the activation's being constitutive of concepts or a mere causal consequence (Barsalou needs the former); and (3) Barsalou's attempt to explain how modal symbols handle abstraction fails.

Preparing words in speech production is normally a fast and accurate process. We generate them two or three per second in fluent conversation; and overtly naming a clear picture of an object can easily be initiated within 600 msec after picture onset. The underlying process, however, is exceedingly complex. The theory reviewed in this target article analyzes this process as staged and feedforward. After a first stage of conceptual preparation, word generation proceeds through lexical selection, morphological and phonological encoding, phonetic encoding, and articulation itself. In addition, the speaker exerts some degree of output control, by monitoring of self-produced internal and overt speech. The core of the theory, ranging from lexical selection to the initiation of phonetic encoding, is captured in a computational model, called weaver++. Both the theory and the computational model have been developed in interaction with reaction time experiments, particularly in picture naming or related word production paradigms, with the aim of accounting for the real-time processing in normal word production. A comprehensive review of theory, model, and experiments is presented. The model can handle some of the main observations in the domain of speech errors (the major empirical domain for most other theories of lexical access), and the theory opens new ways of approaching the cerebral organization of speech production by way of high-temporal-resolution imaging.

Females' tendency to place a high value on protecting their own lives enhanced their reproductive success in the environment of evolutionary adaptation because infant survival depended more upon maternal than on paternal care and defence. The evolved mechanism by which the costs of aggression (and other forms of risk taking) are weighted more heavily for females may be a lower threshold for fear in situations which pose a direct threat of bodily injury. Females' concern with personal survival also has implications for sex differences in dominance hierarchies because the risks associated with hierarchy formation in nonbonded exogamous females are not offset by increased reproductive success. Hence among females, disputes do not carry implications for status with them as they do among males, but are chiefly connected with the acquisition and defence of scarce resources. Consequently, female competition is more likely to take the form of indirect aggression or low-level direct combat than among males. Under patriarchy, men have held the power to propagate images and attributions which are favourable to the continuance of their control. Women's aggression has been viewed as a gender-incongruent aberration or dismissed as evidence of irrationality. These cultural interpretations have “enhanced” evolutionarily based sex differences by a process of imposition which stigmatises the expression of aggression by females and causes women to offer exculpatory (rather than justificatory) accounts of their own aggression.

Although the study of visual perception has made more progress in the past 40 years than any other area of cognitive science, there remain major disagreements as to how closely vision is tied to cognition. This target article sets out some of the arguments for both sides (arguments from computer vision, neuroscience, psychophysics, perceptual learning, and other areas of vision science) and defends the position that an important part of visual perception, corresponding to what some people have called early vision, is prohibited from accessing relevant expectations, knowledge, and utilities in determining the function it computes – in other words, it is cognitively impenetrable. That part of vision is complex and involves top-down interactions that are internal to the early vision system. Its function is to provide a structured representation of the 3-D surfaces of objects sufficient to serve as an index into memory, with somewhat different outputs being made available to other systems such as those dealing with motor control. The paper also addresses certain conceptual and methodological issues raised by this claim, such as whether signal detection theory and event-related potentials can be used to assess cognitive penetration of vision.

A distinction is made among several stages in visual processing, including, in addition to the inflexible early-vision stage, a pre-perceptual attention-allocation stage and a post-perceptual evaluation, selection, and inference stage, which accesses long-term memory. These two stages provide the primary ways in which cognition can affect the outcome of visual perception. The paper discusses arguments from computer vision and psychology showing that vision is “intelligent” and involves elements of “problem solving.” The cases of apparently intelligent interpretation sometimes cited in support of this claim do not show cognitive penetration; rather, they show that certain natural constraints on interpretation, concerned primarily with optical and geometrical properties of the world, have been compiled into the visual system. The paper also examines a number of examples where instructions and “hints” are alleged to affect what is seen. In each case it is concluded that the evidence is more readily assimilated to the view that when cognitive effects are found, they have a locus outside early vision, in such processes as the allocation of focal attention and the identification of the stimulus.

The relations among consciousness, brain, behavior, and scientific explanation are explored in the domain of color perception. Current scientific knowledge about color similarity, color composition, dimensional structure, unique colors, and color categories is used to assess Locke's “inverted spectrum argument” about the undetectability of color transformations. A symmetry analysis of color space shows that the literal interpretation of this argument – reversing the experience of a rainbow – would not work. Three other color-to-color transformations might work, however, depending on the relevance of certain color categories. The approach is then generalized to examine behavioral detection of arbitrary differences in color experiences, leading to the formulation of a principled distinction, called the “isomorphism constraint,” between what can and cannot be determined about the nature of color experience by objective behavioral means. Finally, the prospects for achieving a biologically based explanation of color experience below the level of isomorphism are considered in light of the limitations of behavioral methods. Within-subject designs using biological interventions hold the greatest promise for scientific progress on consciousness, but objective knowledge of another person's experience appears impossible. The implications of these arguments for functionalism are discussed.

Dienes & Perner (D&P) argue that nondeclarative knowledge can take multiple forms. We provide empirical support for this from two related lines of research about the development of mathematical reasoning. We then describe how different forms of procedural and declarative knowledge can be effectively modeled in Anderson's act-r theory, contrasting this computational approach with D&P's logical approach. The computational approach suggests that the commonly observed developmental progression from more implicit to more explicit knowledge can be viewed as a consequence of accumulating and strengthening mental representations.

Cognitive impenetrability (CI) of a large part of visual perception is taken for granted by those of us in the field of computational vision who attempt to recover descriptions of space using geometry and statistics as tools. These tools clearly point out, however, that CI cannot extend to the level of structured descriptions of object surfaces, as Pylyshyn suggests. The reason is that visual space – the description of the world inside our heads – is a nonEuclidean curved space. As a consequence, the only alternative for a vision system is to develop several descriptions of space–time; these are representations of reduced intricacy and capture partial aspects of objective reality. As such, they make sense in the context of a class of tasks/actions/plans/purposes, and thus cannot be cognitively impenetrable.

The scenario used by Dienes & Perner to show that individual representation can be implicit when property representation is explicit can be adapted to show that property representation can be implicit when individual representation is explicit. So there is no hierarchy of explicitness, contrary to their claim. There is a reading of the “implicit/explicit” distinction that does appear to exhibit an asymmetry parallel to that alleged to hold between individual and property. But this is not a distinction Dienes & Perner mention, nor is it one that could be easily incorporated into their framework.

The qualitative and quantitative properties of color sensations and neuronal color coding are discussed in relation to physiological color exchanges and their evolutionary constraints. Based on the identity mind/matter thesis, additional physical measurements on color sensations are described that will allow us, at least in principle, to compare the qualitative properties of color sensations in different brains.

Levelt et al. describe a model of speech production in which lemma access is achieved via input from nondecompositional conceptual representations. They claim that existing decompositional theories are unable to account for lexical retrieval because of the so-called hyperonym problem. However, existing decompositional models have solved a formally equivalent problem.

Campbell's analysis of the evolution of human sex differences to include selection pressures on the female is generally welcomed. This commentary raises some specific issues about the evidence cited: the impact of paternal death on survival prospects; a possible mechanism underlying a sex difference in fear; the selective advantage of dominance hierarchies; and the absence of evidence that testosterone causes human aggression.

Three major attempts by Barsalou to specify what makes a perceptual symbol perceptual fail. One way to give such an account is to use symbols' causal/nomic relation to what they represent, roughly the way contemporary informational psychosemanticists develop their theories, but this fails to draw the distinction Barsalou seems to have in mind.

A comprehensive theory of implicit and explicit knowledge must explain phenomenal knowledge (e.g., knowledge regarding one's affective and motivational states), as well as propositional (i.e., “fact”-based) knowledge. Findings from several research areas (i.e., the subliminal mere exposure effect, artificial grammar learning, implicit and self-attributed dependency needs) are used to illustrate the importance of both phenomenal and propositional knowledge for a unified theory of implicit and explicit mental states.

This commentary discusses Pylyshyn's model of perceptual processing in the light of the philosophical distinction between the conceptual and the nonconceptual content of perception. Pylyshyn's processing distinction maps onto an important distinction in the phenomenology of visual perception.

It is worth considering whether particular behavioral measures from observers are ever consciously (or preattentively) transformed a priori so as to render inferences about them indistinguishable. This is unlikely, but recent experiments indicating color sensitivity and selectivity without visual awareness suggest that the distinction between what can and cannot be explained about color experience using behavioral responses may not be as obvious as Palmer concluded.

Though weaver has knowledge that gets activated by words and pictures, it is incapable of responding appropriately to these words and pictures as task demands are varied. This is because it has a most severe case of attention deficit disorder. Indeed, it has no attention at all. I discuss the very complex attention demands of the tasks given to weaver.

Campbell's evolutionary explanation of women's typically lower rates of interpersonal aggression is plausible, but some supporting evidence requires scrutiny. Women may not commit less interpersonal violence than men against small children. Women are more vulnerable than men in same-sex encounters. The link between dominance and reproductive success for males is less secure than was once thought.

The perceptual symbol approach to knowledge representation combines structured frames and dynamic imagery. The perceptual symbol approach provides a good account of the representation of scientific models, of some types of naive theories held by children and adults, and of certain reconstructive memory phenomena. The ontological status of perceptual symbols is unclear and this form of representation does not succeed in accounting for all forms of human knowledge.

According to Pylyshyn, the early visual system is able to categorize perceptual inputs into shape classes based on visual similarity criteria; it is also suggested that written words may be categorized within early vision. This speculation is contradicted by the fact that visually unrelated exemplars of a given letter (e.g., a/A) or word (e.g., read/READ) map onto common visual categories.

Dienes & Perner argue that volitional control in artificial grammar learning is best understood in terms of the distinction between implicit and explicit knowledge representations. We maintain that direct, explicit access to knowledge organised in a hierarchy of implicitness/explicitness is neither necessary nor sufficient to explain volitional control. People can invoke volitional control when their knowledge is implicit, as in the case of artificial grammar learning, and they can invoke volitional control when any part of their knowledge representation is implicit, as can be seen by examining “feeling of knowing” phenomena.