Evidence from studies of the processing of topographic and classifier constructions in sign language sentences provides a model of how a mental scene description can be represented linguistically, but it also raises questions about how this can be related to spatial linguistic descriptions in spoken languages and their processing. This in turn provides insights into models of the evolution of language.

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.

According to Hurford, PREDICATE (x) is correlated with deictic object variables during event perception. This claim is inconsistent with some core literature on the perception of motion events. We point out that the perception of events involves the activation of the modal properties and amodal properties of underlying event structure, for which Hurford's target article fails to account.

Smith et al.'s article provides a convincing argument for devoting increased research attention to comparative metacognition. However, this increased attention should be complemented with establishing links with comparative theory of mind (ToM) research, which are currently missing. I present a task in which pairs of subjects are presented with incomplete information in an object-choice situation that could be used to establish that link.

Predicate logic has proved a very useful tool for the expression of theories of natural language semantics. Hurford's suggestion that predicate–argument structures mirror certain properties of the human sensorimotor architecture can be seen as an explanation of why this is so. Although I support this view, I think that the correspondences that Hurford draws between linguistic and sensorimotor structures not only involve natural language semantics, but include some elements of natural language syntax as well.

We suggest that the phenomenon of uncertainty monitoring in nonhuman animals contributes richly to the conception of nonhuman animals' self-monitoring. We propose that uncertainty may play a role in the emergence of new forms of behavior that are adaptive. We recommend that Smith et al. determine the extent to which the uncertain response transfers immediately to other test paradigms.

In this commentary, we raise two issues. First, we argue that in any species, the comparative study of metacognitive abilities must be approached from a developmental perspective and not solely from the adult end state. This makes it possible to explore the trajectories by which different species reach their phenotypic outcome and whether different cognitive systems interact over developmental time. Second, using our research comparing different genetic disorders in humans, we challenge the authors' claim that it is unparsimonious to interpret the same performance in humans and animals in qualitatively different ways, because even the same overt behaviour in different groups of humans can be sustained by different underlying cognitive processes.

In animals' natural lives, uncertainty is normal; and certainty, exceptional. Evaluating ambiguous information is essential for survival: Does what is seen, heard, or smelled mean danger? Does that gesture mean aggression or fear? Is he confident or uncertain? If they are conscious of anything, the content of animals' awareness probably includes crucial uncertainties, both their own and those of others.

The objects of attention can be located anywhere along the causal link from the source of stimuli to the final output of the vision system. As causes, they attract and control attention, and as products, they constitute targets of analysis and explicit comments. Stimulus-driven indexing creates pointers that support fast and frugal cognition.

Metaknowledge may not always facilitate acquisition of knowledge or performance of complex tasks. A pigeon, for example, depending on the task, can report what it is doing even if it cannot perform the task well, and it can fail to report what it is doing when it performs the task well (Shimp 1982; 1983).

When animals choose between completing a cognitive task and “escaping,” proper interpretation of their behavior depends crucially on methodological details, including how forced and freely chosen tests are mixed and whether appropriate transfer tests are administered. But no matter how rigorous the test, it is impossible to go beyond functional similarity between human and nonhuman behaviors to certainty about human-like consciousness.

Smith et al. present us with a false dichotomy in explaining their uncertainty data: Either the animals' responses are “under the associative control of stimulus cues,” or the animals must be responding “under the metacognitive control of uncertainty cues.” There is a third alternative to consider: one that is genuinely cognitive, neither associative nor stimulus driven, but purely first-order in character. On this alternative the metacognitive reports of humans in these situations reflect states that are interpretative rather than causal in character.

In the context of Hurford's claim that “some feature of language structure maps onto a feature of primitive mental representations,” I will argue that Hurford's focus on 1-place predicates as the basis of the “mental representations of situations in the world” is problematic, particularly with respect to spatiotemporal events. A solution is proposed.

The predicate-argument approach, focused on perception, is compared with the ease-of-predication (or predicability) approach, focused on encyclopedic knowledge. The latter offers functional prediction and implementation in connectionist models. However, the two approaches characterise predicates in different ways. They thus resemble predicational cantilevers built out from opposite sides of cognition, with a gap that is yet to be bridged.

While the search for the neural basis of the language of thought is a laudable enterprise, and the article by Hurford a valiant first attempt, we argue that in investigating the argument structure of natural language it will ultimately prove more fruitful to consider the restrictions forced on the system by its inherently syntactic character.

The target authors make a strong case for parallels between human and nonhuman metacognition. The case may be bolstered by an appeal to the literatures on commitment and self-control and to that on observing behavior.

Considerations from an interaction-based approach to the evolution of language and the role of word-sentences therein show that the object-attribute ontology is arrived at a much later stage. Therefore, Hurford's arguments, by focusing on the predicate-argument structure, seem to miss out on most of the interesting aspects of the early stages in language evolution.

Hurford presents a much-needed lowly origins scenario for the evolution of conceptual precursors to lexical items. But more is still needed on action, regarding both the message level of lexical concepts and the medium. We summarize our complementary action-based lowly origins (frame/content) scenario for the vocal auditory medium of language, which, like Hurford's scenario, is anchored in a phylogenetically old neurological dichotomy.

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.

Smith et al. present a model that they suggest may clarify aspects of the phylogenetic distribution of metacognition, based on observation of what they call uncertainty monitoring. Although they suggest that their model is supported by data collected using monkeys and dolphins, their interpretation that nonhuman animal behaviors parallel thought processes in humans may be unwarranted. The model presented by Smith et al. is inconsistent with current theories and empirical findings on the comparative aspects of metacognition. We present three oversights of the model and extend our critique to include a brief discussion of animal self-awareness, as well as current neuropsychological perspectives on metacognitive processing in humans.