Our concerns fall into three areas: (1) Barsalou fails to make clear what simulators are (vs. what they do); (2) activation of perceptual areas of the brain during thought does not distinguish between the activation's being constitutive of concepts or a mere causal consequence (Barsalou needs the former); and (3) Barsalou's attempt to explain how modal symbols handle abstraction fails.

Three major attempts by Barsalou to specify what makes a perceptual symbol perceptual fail. One way to give such an account is to use symbols' causal/nomic relation to what they represent, roughly the way contemporary informational psychosemanticists develop their theories, but this fails to draw the distinction Barsalou seems to have in mind.

The perceptual symbol approach to knowledge representation combines structured frames and dynamic imagery. The perceptual symbol approach provides a good account of the representation of scientific models, of some types of naive theories held by children and adults, and of certain reconstructive memory phenomena. The ontological status of perceptual symbols is unclear and this form of representation does not succeed in accounting for all forms of human knowledge.

In his target article, Barsalou cites current work on emotion theory but does not explore its relevance for this project. The connection is worth pursuing, since there is a plausible case to be made that emotions form a distinct symbolic information processing system of their own. On some views, that system is argued to be perceptual: a direct connection with Barsalou's perceptual symbol systems theory. Also relevant is the hypothesis that there may be different modular subsystems within emotion and the perennial tension between cognitive and perceptual theories of emotion.

Barsalou's elision of the personal and sub-personal levels tends to conceal the fact that he is, at best, providing the “specs” but not yet a model for his hypothesized perceptual symbols.

Representational systems need to use symbols as internal stand-ins for distal quantities and events. Barsalou's ideas go a long way towards making the symbol system theory of representation more appealing, by delegating one critical part of the representational burden – dealing with the constituents of compound structures – to image-like entities. The target article, however, leaves the other critical component of any symbol system theory – the compositional ability to bind the constituents together – underspecified. We point out that the binding problem can be alleviated if a perceptual symbol system is made to rely on image-like entities not only for grounding the constituent symbols, but also for composing these into structures.

Understanding the role of simulation in conceptualization has become a priority for cognitive science. Barsalou makes a valuable contribution in that direction. The present commentary points to theoretical issues that need to be refined and elaborated in order to account for key aspects of meaning construction, such as negation, counterfactuals, quantification or analogy. Backstage cognition, with its elaborate bindings, blendings, and mappings, is more complex than Barsalou's discussion might suggest. Language does not directly carry meaning, but rather serves, along with countless other situational elements, as a powerful instrument for prompting its construction

People often solve spatially presented cognitive problems more easily than their nonspatial counterparts. We explain this phenomenon by characterizing space as an inter-modality that provides common structure to different specific perceptual modalities. The usefulness of spatial structure for knowledge processing on different levels of granularity and for interaction between internal and external processes is described. Map representations are discussed as examples in which the usefulness of spatially organized symbols is particularly evident. External representations and processes can enhance internal representations and processes effectively when the same structures and principles can be implicitly assumed.

Amodality is not incompatible with being originally derived from sensory experience. The transformation of perceptual symbols into amodal abstractions could take place spontaneously through self-organizing processes such as autocatalysis. The organizational role played by “simulators” happens implicitly in a neural network, and quite possibly, in the brain as well.

We agree with Barsalou's claim about the importance of perceptual symbols in a theory of abstract concepts. Yet we maintain that the richness of many abstract concepts arises from the metaphorical mapping of recurring patterns of perceptual, embodied experience to provide essential structure to these abstract ideas.

Barsalou proposes (sect. 4.1.6) that perceptual symbols play a role in language processing. Data from our laboratory document this role and suggest the sorts of constraints used by simulators during language comprehension.

In agreement with Barsalou's point that perceptions are not the records or the products of a recording system, and with a nod to an older system in which perception is an activity of testing what future glances bring, I argue that the behavior of perceptual inquiry necessarily makes choices in what is sampled; in what and how the sample is encoded, and what structure across samples is pursued and tested; and when to conclude the inquiry. Much of this is now being hectically rediscovered, but a comprehensive approach like the one Barsalou proposes should help preserve what progress is made.

Barsalou's move to a perceptual basis for cognition is welcome. His scheme contrasts with classical logical schemes in many ways, including its implications for the status of individuals. Barsalou deals mainly with perceived individuals, omitting discussion of cognized individuals. It is argued that the individuality of cognized individuals is an abstraction, which conforms in its manner of formation to other cognitive abstractions which Barsalou discusses, such as truth and disjunction.

A metaphor can often create novel features in an object or a situation. This phenomenon has been particularly hard to account for using amodal symbol systems: although highlighting and downplaying can explain the shift of focus, it cannot explain how entirely new features can come about. We suggest here that the dynamism of perceptual symbol systems, particularly the notion of simulator, provides an elegant account of the creativity of metaphor. The elegance lies in the idea that the creation of new features by a metaphor proceeds in the same way as the creation of regular features in a perceptual symbol.

In their quality as acoustic or visual percepts, words are linked to the emotional values of the state-of-affairs they evoke. This allows them to engender meanings capable of operating nearly entirely detached from percepts. Such a laying flat of meanings permits deliberation to take place within the window of consciousness. In such a theatre of the imagination, linguistically triggered, resides the originality of the human psyche.

Barsalou is right in arguing that perception has been unduly neglected in theories of concept formation. However, the theory he proposes is a weaker version of the classical empirical hypothesis about the relationship between sensation, perception, and concepts. It is weaker because it provides no principled basis for choosing the elementary components of perception. Furthermore, the proposed mechanism of concept formation, growth and development – simulation – is essentially equivalent to the notion of a concept, frame, or theory, and therefore inherits all the well-known problems inherent in these constructs. The theory of simulation does not provide a clearly better alternative to existing notions.

The hypothesis that perceptual mechanisms could have more representational and logical power than usually assumed is interesting and provocative, especially with regard to brain evolution. However, the importance of embodiment and grounding is exaggerated, and the implication that there is no highly abstract representation at all, and that human-like knowledge cannot be learned or represented without human bodies, is very doubtful. A machine-learning model, Latent Semantic Analysis (LSA) that closely mimics human word and passage meaning relations is offered as a counterexample.

Barsalou's contribution converges with basic ideas and empirical findings of cognitive linguistics. They posit the same general architecture. The perceptual grounding of conceptual structure is a central tenet of cognitive linguistics. Our capacity to construe the same situation in alternate ways is fundamental to cognitive semantics, and numerous parallels are discernible between conceptual construal and visual perception. Grammar is meaningful, consisting of schematized patterns for the pairing of semantic and phonological structures. The meanings of grammatical elements reside primarily in the construal they impose on conceptual content. This view of linguistic structure appears to be compatible with Barsalou's proposals.

It is very tempting to try to reconcile perception and cognition perceptual symbol systems may be a good way to achieve this; but is there actually a perception-cognition continuum? We offer several arguments for and against the existence of such a continuum and in favor of the choice of perceptual symbol systems. One of these arguments is purely theoretical, some are based on PET-scan observations and others are based on research with handicapped subjects who have communication problems associated with cerebral lesions. These arguments suggest that modal perceptual symbols do indeed exist and that perception and cognition might have a common neuronal basis; but perceptual and cognitive activities require the activation of different neuronal structures.

The perceptual symbol system view assumes that perceptual representations have a role-argument structure. A role-argument structure is often incorporated into amodal symbol systems in order to explain conceptual functions like abstraction and rule use. The power of perceptual symbol systems to support conceptual functions is likewise rooted in its use of structure. On Barsalou's account, this capacity to use structure (in the form of frames) must be innate.