Perceptual symbol systems form a theoretically plausible alternative to amodal symbol systems. At this point it is unclear whether there is any truly diagnostic empirical evidence to decide between these systems. We outline some possible avenues of research in the domain of language comprehension that might yield such evidence. Language comprehension will be an important arena for tests of the two types of symbol systems.

We can in fact obtain scientific information about the contents of consciousness by the methods of introspectionist psychology. An example comes from the author's work on the stroboscopic patterns and from the way psychedelic drugs alter color perception.

A separation between interpretive and post-interpretive processes is central to Caplan & Waters's theory of language comprehension. This commentary raises some issues that are intended to help sharpen the distinction.

Early childhood is characterized by many cognitive developmentalists as a period of considerable change with respect to representational format. Dienes & Perner present a potentially viable theory for the stages involved in the increasingly explicit representation of knowledge. However, in our view they fail to map their multi-level system of explicitness onto cognitive developmental changes that occur in the first years of life. Specifically, we question the theory's heuristic value when applied to the development of early mind reading and categorization. We conclude that the authors fail to present evidence that dispels the view that knowledge change in these areas is dichotomous.

The commentator agrees with Pylyshyn's most general claims but sees problems with the more specific proposals about where the boundary between early vision and later processing might lie. The boundary cuts across current models of identification. Limitations in current research on scenic context effects preclude firm conclusions. High-level vision will benefit more from integrative work than from premature analysis.

Pulvermüller assumes that words are represented as associations of two cell assemblies formed according to Hebb's coincidence rule. This seems to correspond to the linguistic notion that words consist of lexemes connected to lemmas. Standard examples from theoretical linguistics, however, show that lemmas and lexemes have properties that go beyond coincidence-based assemblies. In particular, they are inherently disposed toward combinatorial operations; push-down storage, modelled by decreasing reverberation in cell assemblies, cannot capture this. Hence, even if the language capacity has an associationist characterization at some level, it cannot just be co-occurrence-based assembly formation.

Word class-specific differences in brain evoked potentials (EP) are discussed for connotative meaning and for function versus content words. A well-controlled experiment found matching lexical decision times for function and content words, but clear EP differences (component with maximum near 550 msec) among function words, content words, and nonwords that depended on brain site. Another EP component, with a 480 msec maximum, differentiated words (either function or content) from nonwords.

Pylyshyn's concentration on form perception to demonstrate that early vision is cognitively impenetrable neglects that color perception is also part of early vision. Thus, the finding of Duncker (1939), Bruner et al. (1951), and Delk and Fillenbaum (1965) that the expected color of objects affects how they are perceived challenges Pylyshyn's thesis.

This commentary considers how far one can go in making inferences about functional modularity or segregation, based on the sorts of analyses used by Caplan & Waters in relation to the underlying neuronal infrastructure. Specifically, an attempt is made to relate the “functionalist” approach adopted in the target article to “neuroreductionist” perspectives on the same issue.

This commentary focuses on how Dienes & Perner's (D&P's) claims relate to aspects of development. First, I discuss recent research that supports D&P's claim that anticipatory looking in a false belief task is guided by implicit knowledge. Second, I argue that implicit knowledge may be based on exposure to regularities in the world as D&P argue, but equally, it may sometimes be based on theories that conflict with real world regularities. Third, I discuss Munakata et al.'s notion of graded representations as an alternative to the implicit-explicit distinction in explaining dissociations in infancy.

I defend the possibility of a functional account of the intrinsic qualities of sensory experience against the claim that functional characterization can only describe such qualities to the level of isomorphism of relational structures on those qualities. A form sensory holism might be true concerning the phenomenal, and this holism would account for some antifunctionalist intuition evoked by inverted spectrum and absent qualia arguments. Sensory holism is compatible with the correctness of functionalism about the phenomenal.

Prior to the twentieth century, theories of knowledge were inherently perceptual. Since then, developments in logic, statistics, and programming languages have inspired amodal theories that rest on principles fundamentally different from those underlying perception. In addition, perceptual approaches have become widely viewed as untenable because they are assumed to implement recording systems, not conceptual systems. A perceptual theory of knowledge is developed here in the context of current cognitive science and neuroscience. During perceptual experience, association areas in the brain capture bottom-up patterns of activation in sensory-motor areas. Later, in a top-down manner, association areas partially reactivate sensory-motor areas to implement perceptual symbols. The storage and reactivation of perceptual symbols operates at the level of perceptual components – not at the level of holistic perceptual experiences. Through the use of selective attention, schematic representations of perceptual components are extracted from experience and stored in memory (e.g., individual memories of green, purr, hot). As memories of the same component become organized around a common frame, they implement a simulator that produces limitless simulations of the component (e.g., simulations of purr). Not only do such simulators develop for aspects of sensory experience, they also develop for aspects of proprioception (e.g., lift,run) and introspection (e.g., compare,memory,happy, hungry). Once established, these simulators implement a basic conceptual system that represents types, supports categorization, and produces categorical inferences. These simulators further support productivity, propositions, and abstract concepts, thereby implementing a fully functional conceptual system. Productivity results from integrating simulators combinatorially and recursively to produce complex simulations. Propositions result from binding simulators to perceived individuals to represent type-token relations. Abstract concepts are grounded in complex simulations of combined physical and introspective events. Thus, a perceptual theory of knowledge can implement a fully functional conceptual system while avoiding problems associated with amodal symbol systems. Implications for cognition, neuroscience, evolution, development, and artificial intelligence are explored.

Holistically ignited Hebbian models are fundamentally different from the serially organized connectionist implementations of language. This may be important for the recovery of language after injury, because connectionist models have provided useful insights into recovery of some cognitive functions. I ask whether cell assembly modelling can make an important contribution and whether the apparent incompatibility with successful connectionist modelling is a problem.

We discuss several issues raised by Caplan & Waters's distinction between interpretative and post-interpretative processes in sentence comprehension, including the nature and properties of the two systems, problems with measuring their respective capacities, and the relationship between the hypothesized separate-language-interpretation-resource (SLIR) and the general verbal working memory system that supports post-interpretive processing.

We applaud Dienes & Perner's efforts while raising some concerns regarding their assimilation of diverse data into a unifying framework. Some of the findings need not fit the framework they suggest. It is also not always clear what, above logico-semantic consistency, assimilation adds to the data that do fit their framework. These concerns are highlighted with reference to their arguments regarding the developmental data and the neuropsychological data, respectively.

It is argued that given the task Palmer sets himself, there are no constraints on his colour experiences whatsoever.

Various defenses of amodal symbol systems are addressed, including amodal symbols in sensory-motor areas, the causal theory of concepts, supramodal concepts, latent semantic analysis, and abstracted amodal symbols. Various aspects of perceptual symbol systems are clarified and developed, including perception, features, simulators, category structure, frames, analogy, introspection, situated action, and development. Particular attention is given to abstract concepts, language, and computational mechanisms.

Pylyshyn acknowledges that cognition intervenes in determining the nature of perception when attention is allocated to locations or properties prior to the operation of early vision. I present evidence that scale perception (one function of early vision) is cognitively penetrable and argue that Pylyshyn's criterion covers not a few, but many situations of recognition. Cognitive penetrability could be their modus operandi.

Individuals may differ in the general-attention executive component or in the subordinate domain-specific “slave” components of working memory. Tasks requiring sustained memory representations across attention shifts are reliable, valid indices of executive abilities. Measures emphasizing specific processing skills may increase reliability within restricted samples but will not reflect the attention component responsible for the broad predictive validity of span tasks.

Pylyshyn's target article argues that perception is not inferential, but this is true only under a narrow construal of inference. A more general construal is possible, and has been used to provide formal theories of many visual capacities. This approach also makes clear that the evolution of natural constraints need not converge to the “veridical” state of the world.