The multiple levels of analysis that Quartz & Sejnowski (Q&S) bring to bear on the phenomenon of activity-driven dendritic growth show the tight linkage of explanations from the cellular to the cognitive level. To show how multiple control regimes can intersect at the same site, I further elaborate an example of a developmental problem solved at the axodendritic connection: that of population matching.

We need to reconsider and reconceive the path that will take us from innate perceptual saliencies to basic (and perhaps other) colour language. There is a space between the perceptual and the linguistic levels that needs to be filled by an account of the rules that people use to generate relatively stable reference classes in a social context.

Glenberg's conception of “meaning from and for action” is too narrow. For example, it provides no satisfactory account of the “logic of Elfland,” a metaphor used by Chesterton to refer to meaning acquired by being told something.

All that we call spirit and art and ecstasy only means that for one awful instant we remember that we forget.

G. K. Chesterton (in Gardner 1994, p. 101)

The target articles by blumberg et al. and berkley reflect some of the recent major theoretical and clinical advances in two areas of pain research. These two articles also represent two very different approaches to which type of variables are considered relevant to the study of pain. These different approaches are contrasted in the context of the different emphases in pain and pleasure research.

The persistence of both inflammatory and neuropathic pain can only be explained when learning processes are taken into account in addition to sensitizing mechanisms. Learning processes such as classical and operant conditioning create memories for pain that are based on altered synaptic connections in supraspinal structures and persist without peripheral input. [coderre & katz; dickenson; wiesenfeld-hallin et al.]

Quartz & Sejnowski's (Q&S's) main accomplishment is the presentation of increasing complexity in the developing brain. Although this cuts a colorful swath through current theories of learning, it leaves the central question untouched: How does the environment direct neural structure? In answer, Q&S offer us only Hebb's half-century-old suggestion once again.

The following provides further arguments for the nonuniversality of color as an autonomous dimension. Research on odors suggests that there are cultural constraints on the abstraction of dimensions for objects. Color vision analysis leads to an overemphasis on the role of perceptual processes in categorization. The study of odors points to human activities as a more important principle of categorization that drives the perceptual processing and suggests a reconsideration of vision itself.

Glenberg provides a new and exciting view that is especially useful for capturing some functional aspects of memory. However, memory and its functions are too multifarious to be handled by any one conceptualization. We suggest that Glenberg's proposal be restricted to its own “focus of convenience.” In addition, its value will ultimately depend on its success in generating detailed and testable theories.

Glenberg focuses on conceptualizations that change from moment to moment, yet he dismisses the concept of working memory (sect. 4.3), which offers an account of temporary storage and on-line cognition. This commentary questions whether Glenberg's account adequately caters for observations of consistent data patterns in temporary storage of verbal and visuospatial information in healthy adults and in brain-damaged patients with deficits in temporary retention.

I agree with Quartz & Sejnowski's (Q&S's) points, which are familiar to many scientists. A number of models with the sought-after properties, however, are overlooked, while models without them are highlighted. I will review nonstationary learning, links between development and learning, locality, stability, learning throughout life, hypothesis testing that models the learner's problem domain, and active dendritic processes.

Despite the heat of their attack, Saunders & van Brakel do illuminate various shortcomings of color research in the tradition of Berlin & Kay. Berlin and Kay elicit a pan-cultural pattern in color language, but the pattern does not provide much insight into the human mind.

berkley's pathogen model of sex differences in pain is inconsistent with women outliving men by several years. The vagina is far more resistant to pathogens than is the rectum. Vaginal stimulation produces intense analgesia in rats and humans. Possible evolutionary and cardiovascular factors are also noted.

In adult humans, conscious visual experience – including that of colour – is shaped by particular cultural practices, as evidenced in the cross-cultural literature. In addition, the practices of our own culture already inform attempts to assess the “natural” experience of newborns or other animals.

Processing limitations can be an advantage for a learner (Elman 1993; Newport 1990; Turkewitz 1982). They can filter input to the learner so that the relations to be learned increase in complexity only gradually. The time-course of filtered input can complement the growing neural representations discussed by Quartz & Sejnowski.

To model potential interactions, memory must not only mesh prior patterns of action, as Glenberg proposes, but also their internal consequences. This is necessary both to discriminate sensorimotor information by its relevance and to explain how go als about the world develop. In the absence of internal feedback, Glenberg is forced to reintroduce a grounding problem into his otherwise sound model by presupposing interactive goals.

Recent pain research has concentrated heavily on excitatory processes. However, noxious stimuli activate excitatory and inhibitory systems. As failure of inhibition could underlie some forms of pathological pain, it may be argued that a full understanding of the mechanisms underlying the development of pain states can only come from a consideration of all the central sequelae of injurious stimuli. [berkley; blumberg et al.; coderre & katz; dickenson; mcmahon; weisenfeld-hallin et al.]

Hyperalgesia can arise from peripheral sensitization, on-going peripheral activation, and central plasticity. In the target article, coderre & katz argue that all three mechanisms contribute to hyperalgesia. In contrast, we believe that existing experimental evidence suggests that central plasticity plays only an insignificant role in most experimental models and clinical presentations of hyperalgesia induced by tissue injury or chemical activation of sensory receptors.

Can memory be cast as a system that meshes events to actions? This commentary considers the concepts of mesh versus association, arguing that thus far the distinction is inadequate. However, the goal of shifting to an action-based view of memory has merit, most notably in emphasizing memory as a skill and in focusing on processes as opposed to structures.

There is evidence for increase, followed by decline, in synaptic numbers during development. Dendrites do not function in isolation. A constructive neuronal process may underpin a selectionist cognitive process. The environment shapes both ontogeny and phylogeny. Phylogenetic natural selection and neural selection are compatible. Natural selection can yield both constructivist and selectionist solution to adaptuive problems.

If, as Saunders & van Brakel assert, hue, lightness, and saturation characterize artificial color spaces and not the colors of everyday life, one would expect those color spaces to have limited relevance to our understanding of color phenomena and to be of little practical application. This is not the case. Although people perceive these and equivalent color dimensions holistically rather than analytically, they are able to use such triples to categorize the colors of their environment.