There is not enough reason to believe that syllables are primary in speech and evolved from the cyclic movements of chewing. There are many differences between chewing and speech and it is equally plausible that what is primary in speech is a succession of auditorily robust modulations of various acoustic parameters (amplitude, periodicity, spectrum, pitch); syllables could have evolved from this.

Locus equations offer promise for an understanding of at least some aspects of perceptual invariance in speech, but they were discovered almost fortuitously. With the present availability of powerful machine learning algorithms, ignorance-based automatic discovery procedures are starting to supplant knowledge-based scientific inquiry. Principles of self-learning and self-organization are powerful tools for speech research but remain somewhat under-utilized.

There are three points of difference between psychologists' assumptions and those that Millikan suggests: (1) concepts as representations versus concepts as reflecting a capacity; (2) concepts having a role in categorization and inference versus a role in reidentification; and (3) the “basic level” as an aspect of the “vertical” dimension of categories versus being a kind of category, on a par with natural kinds.

It is suggested (1) that motivation must not be overlooked, (2) that most social imitation does not involve novel behaviors, and (3) that newborn babies do imitate.

A realist story of concepts like Millikan's can and should accommodate facts about how the context of items available for comparison during concept formation affects just what concept is formed or reidentified. Similarly, the contribution of the goals and purposes of the conceptualizer are relevant to how concepts are acquired and deployed, but can be understood as entirely consistent with a view of concepts as objectively evaluable.

In their important work on locus equations, Sussman and his colleagues have helped to simplify the theoretical problem of how human listeners identify place of articulation contrasts among consonants, but much work remains before this problem is solved.

Four aspects of Mazur & Booth's target article are discussed from a comparative perspective using teleost fish as a reference: (a) the relationship between aggression, dominance, and androgens; (b) the interpretation of the data in light of the challenge hypothesis; (c) the potential role of testosterone as a physiological mediator between social status and the expression of male characters; and (d) the fact that metabolic conversions of testosterone may be important in its effect on aggression/ dominance.

Byrne & Russon use novelty as the primary requirement for providing evidence of true imitation in animals. There are three reasons to object to this. First, experiential learning cannot always be completely excluded as an alternative explanation of the observed behavior. Second, the imitator's manipulations performed during ontogeny cannot be known in full detail. Finally, there is at present only a weak understanding of how novel forms emerge. Data from our own recent experiments will be used to emphasize the need for a tighter methodology in imitation experiments.

Relational complexity theory has important virtues, but the present model omits key aspects and evidence. In contrast, skill theory specifies (1) a detailed series of developmental changes in relational complexity from birth to age 30, (2) processes of interaction of content and structure that produce variability in complexity, (3) the role of cortical development, and (4) empirical criteria for complexity levels, including developmental discontinuities. Many findings support these specifications.

The target article raises the question of whether transcription-based evidence is sufficient to support assumptions relating to patterns of mandibular activity in young children. Studies on the perception of both adult and infant speech indicate that the argument needs to be reexamined on the basis of acoustic and articulatory data.

Much of the material MacNeilage cites to support his frame/content theory for the evolution of speech production in humans is not unique to mammals. Parallels can be drawn for comparable evolution of vocal flexibility (specifically the reproduction of human speech) in birds. I describe several such parallels and conclude that MacNeilage's hypotheses may have broader application than he envisioned.

I discuss neuroscientific and phenomenological arguments in support of Millikan's thesis. I then consider invariance as a unifying theme in perceptual and conceptual tracking, and how invariants may be extracted from the environment. Finally, some wider implications of Millikan's nondescriptionist approach to language are presented, with specific application to color terms.

Evidence from many species suggests that social, developmental, and cognitive variables are important influences on aggression. Few direct activational or organizational effects of hormones on aggression and dominance are found in nonhuman primates. Female aggression and dominance are relatively frequent and occur with low testosterone levels. Social, cultural, and developmental mechanisms have more important influences on dominance and aggression than hormones.

Byrne & Russon's target article displays all the difficulties encountered when one fails to take a methodological behaviourist approach to imitation. Their conceptual apparatus is grounded in a mixture of introspection and folk psychology. Their distinction between action-level and program-level imitation falters on goal imputation for sequential acts. In an alternative gradient descent model, behaviour can be simulated as a frustration/satisfaction gradient descent in the animal's “potentiality space,” as defined by knowledge, inventiveness, and the surrounding environment.

Locus equations contain an economical set of hidden (i.e., not directly observable in the data) parameters of speech that provide an elegant way of characterizing the ubiquitous context-dependent behaviors exhibited in speech acoustics. These hidden parameters can be effectively exploited to constrain the huge set of context-dependent speech model parameters currently in use in modern, mainstream speech recognition technology.

Halford et al. have sharpened the concept of processing capacity as applied to various complex tasks. This commentary examines the apparent contradiction between capacity theories and theories in which it is processing speed, rather than capacity, that presumably limits cognitive performance. It explains how capacity and speed often are interrelated and suggests how one might examine whether capacity or speed is the more elementary in processing.

Tests of models of reciprocal interactions of testosterone and behaviour patterns in honour subcultures, if based on adult samples measured at a single point in time, would be aided by measures of behaviour in such samples that indirectly index basal testosterone levels at earlier developmental ages, for example, hand preference and other measures of cerebral dominance. Such models raise questions about the social preconditions of honour subcultures, and their indirect effects on health.

Even in infancy, concept formation has to do with creating meaning, not with tracking substances. Preverbal infants can identify a substance such as a dog, but their first concept of this substance is not dog but animal. It is difficult to account for such global concepts by the perceptual processes involved in object identification, yet these concepts are the foundation on which later concepts are built.

Relational complexity provides a metric for measuring task demands, and in this respect has much in common with the cognitive complexity and control theory. However, relational complexity does not account for the relative difficulty of different relational types, and appears to underestimate the importance of changes in children's ability to act on the basis of their understanding.

Sussman and colleagues provide no evidence supporting their claim that the human vocal production system is specialized to produce locus equations with high correlations and linearity. We propose the alternative null hypothesis that these features result from physical and physiological factors common to all mammalian vocal tracts and we recommend caution in assuming that human speech production mechanisms are unique.