Smith et al. propose that the most parsimonious explanation for identical responses of humans and nonhumans under the same conditions is not always the simplest cognitive explanation but could be the one that has the most logical consistency across species. The authors provide convincing evidence and a reasonable argument for declarative consciousness as a shared psychological property in humans, monkeys, and dolphins.

One supposition underlying the Anderson & Lebiere (A&L) target article is that the maximally broad “encompassing of its subject matter – the behavior of man” (cf. sect. 6, last para.) is regarded as an unquestioned quality criterion for guiding cognitive research. One might argue for an explicit specification of the limitations of a given paradigm, rather than extending it to apply to as many domains as possible.

Reichle et al. show that saccades in reading are controlled by linguistic processing. The authors' Figure 13 shows the parietal and frontal eye fields as parts of a neural implementation. This commentary presents data from dyslexics performing nonreading saccade tasks. The dyslexics exhibit deficits in antisaccade control. Improvement of the deficits is achieved in 85% of the cases and results in advantages in learning how to read.

The reflectance types that Byrne & Hilbert identify with colors count as types only in a way that is more dependent on, and more relative to color perceivers, than their account suggests. Their account of perceptual content may be overly focused on input conditions and distal causes.

Corballis presents a plausible evolutionary mechanism to explain the tight linkage between cerebral lateralization for language and for handedness in humans. This argument may be bolstered by invoking Stokoe's notion of semantic phonology to explain the role of Broca's area in grammatical functions.

The very clever studies reviewed by Smith et al. convincingly demonstrate metacognitive skills in animals. However, interpreting the findings on metacognitive monitoring as showing conscious cognitive processes in animals is not warranted, because some metacognitive monitoring observed in humans appear to be automatic rather than controlled.

The authors favor a “color realism” theory that considers colors to be physical properties residing in objects that reflect, emit, or transmit light. It is opposed to the theory that colors are sensations or visual experiences. This commentary suggests that both theories are correct, and that context usually indicates which of these dual aspects is being considered.

The target article is based upon the principle that complex mental phenomena result from the interactions among some elementary entities. Connectionist nodes and ACT-R's production rules can be considered as such entities. However, before testing against Newell's macro-criteria, self-organizing models must be tested against criteria relating to the properties of their elementary entities. When such micro-criteria are considered, they separate connectionism from ACT-R and the comparison of these theories against Newell's Tests is hardly correct.

The authors' review of alternative models for reading is of great value in identifying issues and progress in the field. More emphasis should be given to distinguishing between models that offer an explanation for behavior and those that merely simulate experimental data. An analysis of a model's discrete structure can allow for comparisons of models based upon their inherent dimensionality and explanatory power.

In attempting to integrate the authors' proposed model with results from analogous human event-related potential (ERP) research, we found difficulties with: (1) its apparent disregard for supraordinate representations at posterior multimodal association cortices, (2) its failure to address contextual task effects, and (3) its strict architectural dichotomy between memory storage and control functions.

A central component in the E-Z Reader model is a two-stage word processing mechanism made responsible for both the triggering of eye movements and sequential shifts of attention. We point to problems with both the verbal description of this mechanism and its computational implementation in the simulation. As an alternative, we consider the use of a connectionist processing module in combination with a more indirect form of cognitive eye-movement control.

The distinction between such differing approaches to cognition as connectionism and rule-based models is paralleled by a distinction between two basic modes of cognition postulated in the so-called dual-process theories. Integrating these theories with insights from hybrid systems might help solve the dilemma of combining the demands of evolutionary plausibility and computational universality. No single approach alone can achieve this.

Our reply is in three parts. The first part concerns some foundational issues in the debate about color realism. The second part addresses the many objections to the version of physicalism about color (“productance physicalism”) defended in the target article. The third part discusses the leading alternative approaches and theories endorsed by the commentators.

The present commentary agrees with many of the points made by Ruchkin et al., but brings up several important differences in assumptions. These assumptions have to do with the nature of the capacity limit in working memory and the possible bases of working-memory activation.

The role of Broca's area is currently unclear even with regard to language. Suggestions that this area was enlarged on the left in certain of our hominid ancestors are unconvincing. Broca's area may have nothing to do with a lateralized gestural or vocal system Handedness may have evolved more than four million years ago.

Several conclusions depend on a version of signal detection theory that assumes performance is based on underlying equal-variance normal distributions of trace strength. Such conclusions are questionable without empirical justification for that assumption. A thought experiment is presented to show how the assumption is probably invalid, and empirical evidence is cited for the assumption's invalidity in research on human memory.

This commentary defines an additional characteristic of human learning. The nature of this test is different from the ones by Newell: This is a hard, pass/fail type of test. Thus a theory of cognition cannot partially satisfy this test; it either conforms to the requirement fully, or it doesn't. If a theory of cognition cannot satisfy this property of human learning, then the theory is not valid at all.

Ruchkin et al. use brain-activity data from healthy subjects to assess the physiological validity of a cognitive working memory model and to propose modifications. The conclusions drawn from this data are interesting and plausible, but they have limitations. Much of what is known about the neural mechanisms of working memory comes from single neuron recordings in animals, and it is currently not fully understood how these translate to scalp recordings of EEG.

Only two of the many experiments described by Smith et al., as indicating metacognitive ability in nonhuman animals, involved metacognition as understood in the human literature. Of these, one gave negative results. In the other, one of two rhesus monkeys provided data suggesting that he might have metacognitive ability. The conjecture that any nonhuman animals have metacognitive ability is, therefore, tenuous.

An intervening gestural stage in language evolution, though seductive, is ultimately redundant, and is not necessarily supported by modern human or chimp behaviour. The findings and arguments offered from mirror neurones, anatomy, and lateralization are capable of other interpretations, and the manipulative dextrality of chimps is under-recognized. While language certainly possesses certain unique properties, its roots are ancient.