Increased complexity of representations in development probably results from the differentiation of distributed neural circuits. Axonal differentiation plays a crucial role in this process. Axonal differentiation appears to be achieved in stages, each involving combinations of constructive and regressive events controlled by cell intrinsic and cell extrinsic information.

This commentary starts with a simplified Cartesian vector space of the tristimulus theory of color. This vector space is then further simplified so that bitstrings are used to represent the vector space. The Commission Internationale de l'Eclairage (CIE) diagram is shown to follow directly and simply from this vector space. The Berlin & Kay results are shown to agree quite well with the vector space and the two-dimensional version of it, especially if the dimensions are normalized to take into account the sensitivity of the eye to the different wavelengths comprising color. There is asymmetry with respect to the colors and a similar asymmetry in vocalic phonemes; these effects can be explained in terms of physiology. The (in)famous problem of the color channels is given a unified treatment at various levels. An eight-valued color algebra is created, with addition and multiplication corresponding to additive and subtractive blending of colors. Finally, it is shown that the discrete Hamming metric for colors has a natural toroidal topology.

Evidence that central sensitization needs to be maintained in an ongoing manner by nociceptive input from the periphery makes the peripheral drive, rather than the central amplification process, the highest priority target for understanding and control. To stop the peripheral drives to kill two birds with one stone. Moreover, the amplification that central sensitization does provide is selective and not necessarily striking in intensity. A “magic bullet” that neutralized central sensitization would probably be less effective in controlling persistent pain than many investigators would like to believe. [berkley; blumberg et al.; coderre & katz; dickenson; mcmahon; weisenfeld-hallin et al.]

Glenberg tries to explain how and why memories have semantic content. The theory succeeds in specifying the relations between two major classes of memory phenomena – explicit and implicit memory – but it may fail in its assignment of relative importance to these phenomena and in its account of meaning. The theory is syntactic and extensional, instead of semantic and intensional.

We add to the constructivist approach of Quartz & Sejnowski (Q&S) by outlining a specific classification of sources of constraint on the emergence of representations from Elman et al. (1996). We suggest that it is important to consider behavioral constructivism in addition to neural constructivism.

Patients with reflex sympathetic dystrophy (RSD) affecting one limb show similar sympathetic traffic in nerves supplying the affected and unaffected limb, despite unilateral autonomic effector dysfunction. This argues against the notion that RSD is mediated by a reflex change in the pattern of sympathetic discharge and underlines the fact that autonomic effector disturbances give little information about underlying nerve traffic. [blumberg et al.]

There are three major weaknesses with Glenberg's theory. The first is that his theory makes assumptions about internal representations that cannot be adequately tested. The second is that he tries to accommodate data from three disparate domains: mental models, linguistics, and memory. The third is that he makes light of advances in cognitive neuroscience.

Zone theories of color vision transform cone sensitivities to channel sensitivities before transmitting these signals to the brain. The concepts of “unique hue” and “color opponency” are fundamental to an understanding of this transformation. Saunders & van Brakel question the objectivity of these concepts. Statements in their target article indicate that the reason for this questioning stems from a failure to appreciate the constraints inherent in the definitions of these concepts.

Signal-detection methodology may be used to disentangle sensory from judgmental effects when analyzing sex differences in pain. An illustrative example is given by reanalyzing a published category-scaling experiment in terms of detection-theory indices. As a result, the apparent sex difference is recast in terms of a judgmental bias. [berkley]

The functional theory of memory set out in Glenberg's target article accords with recent proposals in the developmental literature with respect to event memory, conceptualization, and language acquisition from an embodied, experiential view. The theory, however, needs to be supplemented with a recognition of the sociocultural contribution to these cognitive processes and emerging structures.

A credible account of the neurobiology underlying cognitive development cannot afford to ignore the recently demonstrated innate regionalisation of the neocortex as well as the ontogeny of corticocortical phenomena, only for the latter does the timing of development permit control by external events and this is most likely to occur at later stages in the fine tuning of cortical microcircuitry.

Saunders & van Brakel set out to review color science research and to topple the belief that color-vision neurophysiology sets strong deterministic constraints on the cognitive processing of color. Although their skeptism and mission are worthwhile, they fail to give proper treatment to (1) findings that dramatically support some positions they aim to tear down, (2) existing research that anticipates criticisms presented in their target article, and (3) the progress made in the area toward understanding the phenomenon. At the very minimum these oversights weaken the credibility of their arguments and leave the reader to wonder why their discussion ignores what is clearly omitted.

What would Glenberg's attractive ideas look like when computationally fleshed out? I suggest that the most helpful next step in formalizing them is neither a connectionist nor a symbolic implementation (either is possible), but rather an implementation- general analysis of the task in terms of the informational content required.

The argument of berkley for the existence sex differences in pain is based on biological factors. We suggest that the psychological evidence for such differences is more substantial.

Saunders & van Brakel's claim that Berlin and Kay (1969) assumed a language/vision correlation in the area of color categorization and disguised this assumption as a finding is shown to be false. The methodology of the World Color Survey, now nearing completion, is discussed and the possibility of an additional language/vision correlation in color categorization is suggested.

Missing from Quartz & Sejnowski's (Q&S's) unique and valuable effort to relate cognitive development to neural constructivism is an examination of the global emergent properties of adding new neural circuits. Such emergent properties can be studied with computational models. Modeling with generative connectionist networks shows that synaptogenic mechanisms can account for progressive increases in children's representational power.

Although the idea that cognitive structure changes as we learn is welcome, a variety of mathematical structures are needed to model the neural and cognitive processes involved. A specific example of bodily-kinaesthetic intelligence is given, building on a formalism given elsewhere. As the structure of cognition changes, previous learning can become tacit, adding to the complexity of cognition and its modeling.

There is no natural and pretheoretical classification of colour appearances into hue, saturation, brightness, unique hues, and so on. Rather, our theoretical insights into the coding of colour have reciprocally shaped the way we talk about colour appearances. Opponency is only one of many fundamental aspects of colour coding, and we are hardly justified in ascribing some theoretical prominance to it.

In patients with pain characterized by a painful focus and allodynia, the painful symptoms arise from altered central processing that is initiated and subsequently maintained by persistent input from nociceptive afferents. Treatments directed at this normal consequence of persistent input are inherently limited. The most efficacious treatments will target the pathology, the various sources of ongoing nociceptor input. [blumberg et al.; coderre & katz; dickenson]

The ability of Glenberg's model to explain the development of complex symbolic abilities is questioned. Specifically, it is proposed that the concepts of clamping and suppression fall short of providing an explanation for higher symbolic processes such as autobiographical memory and language comprehension. A related concept, “holding in mind” (Olson 1993), is proposed as an alternative.