Within the context of Carruthers’ general analysis of the relation between language and thought, I present a specific hypothesis about how grammar uses perspective flow to unify disparate cognitions. This perspective hypothesis allows us to understand the neolithic burst in creativity as a cultural advance in methods for knitting together thoughts.

First, the importance of language in cognition is recognized. Nevertheless, this does not necessarily imply that the locus of thought is natural language (words, syntax, phonology). Then, difficulties with some of Carruthers’ hypotheses are stated: Is an account based on LFs capable of dealing with the complexities involved in what we call thought? Finally, mention of the issue of language production is made.

Cross-domain representations provide the foundation for language and are not its unique product. Modularity of a limited kind is confined to early infancy in humans and is succeeded by domain-general thinking and speaking. Representational language becomes accessible to the cognitive system during the preschool years as a supplement to experientially based conceptual processing, resulting in a dual-process system.

Carruthers presents evidence concerning the cross-modular integration of information in human subjects which appears to support the “cognitive conception of language.” According to this conception, language is not just a means of communication, but also a representational medium of thought. However, Carruthers overlooks the possibility that language, in both its communicative and cognitive roles, is a nonrepresentational system of conventional signals – that words are not a medium we think in, but a tool we think with. The evidence he cites is equivocal when it comes to choosing between the cognitive conception and this radical communicative conception of language.

Carruthers clearly identifies the basic issues involved in language and thought relations and argues for an adaptive central model. Similar conclusions were reached by classical research in the inner speech tradition. Sokolov (1968; 1972) especially emphasized that inner speech appears only when the task is difficult. The use of inner speech is not a necessity to transform representations, but it is called for when transformations become difficult. This might be related to the cognitive reorganizations leading to language as emphasized by Donald (2001).

Carruthers argues that natural language is the medium of non-domain-specific thought in humans. The general idea is that a certain type of thinking is conducted in natural language. It’ not exactly clear, however, what type of thinking this is. I suggest two different ways of interpreting Carruthers’ thesis on this point and argue that neither of them squares well with central-process modularism.

A central claim of the target article is that language is the medium of domain-general, cross-modular thought; and according to Carruthers, the main, direct evidence for this thesis comes from a series of fascinating studies on spatial reorientation. I argue that the these studies, in fact, provide us with no reason whatsoever to accept this cognitive conception of language.

Carruthers’ notion that natural language(s) might serve as the medium of non-domain-specific, propositionally based inferential thought is extended to the case of effortful retrieval of autobiographical memory among bilinguals. Specifically, the review suggests that the resources of bilingual inner speech might play a role in the cyclical activation of information from various informational domains during memory retrieval.

The possible role of language in intermodular communication and non-domain-specific thinking is an empirical issue that is independent of the “vehicle” claim that natural language is “constitutive” of some thoughts. Despite noting objections to various forms of the thesis that we think in language, Carruthers entirely neglects a potentially fatal objection to his own preferred version of this “cognitive conception.”

Carruthers’ “mentalese expressions” take the form of English sentences, thus suggesting an isomorphism between thought and language that ignores linguistic diversity. Furthermore, complex syntax is not the only linguistic means of combining information from various domain-specific modules into domain-general expressions, nor is such syntax the preferred means of encoding basic experiences in all languages. The analysis seems to rest on an unacknowledged version of linguistic determinism.

The hypothesis that nonhuman species, lacking verbal language, do not really integrate information from different modules, but use instead information sequentially, appears difficult to put under empirical scrutiny. Evidence is discussed showing that in nonhuman species storing of geometric information occurs spontaneously even when landmark information suffices for spatial reorientation, suggesting simultaneous encoding, if not use, of information from different modules.

We examine Carruthers’ proposal that sentences in logical form serve to create flexibility within central system modularity, enabling the combination of information from different modalities. We discuss evidence from aphasia and the neurobiology of input-output systems. This work suggests that there exists considerable capacity for interdomain cognitive processing without language mediation. Other challenges for a logical form account are noted.

Models of working memory challenge some aspects of Carruthers’ account but enhance others. Although the nature of the phonological store and central executive appear fully congruent with Carruthers’ proposal, current models of the visuo-spatial sketchpad provide a better account of skilled action. However, Carruthers’ model may provide a way around the homunculus problem that has plagued models of working memory.

Perhaps in addition to language being a potential medium of domain-general thought, as suggested by Carruthers, language may also play another role in conceptual development: Words are “essence placeholders.” Evidence is presented from studies on categorization, object individuation, and inductive inference in infancy. The assumption that words are essence placeholders may be a mechanism by which infants acquire kind concepts.

The present response elucidates, elaborates, and defends the main thesis advanced in the target article: namely, that natural-language sentences play a constitutive role in some human thought processes, and that they are responsible for some of the distinctive flexibility of human thinking, serving to integrate the outputs of a variety of conceptual modules. Section R1 clarifies and elaborates this main thesis, responding to a number of objections and misunderstandings. Section R2 considers three contrasting accounts of the mechanism of intermodular integration. Section R3 discusses objections to some of the empirical data supporting my main thesis. Section R4 criticizes some competing theories of the role of language in cognition. And section R5 considers some proposed supplementary cognitive roles that language might play.

It is often assumed that similar domain-specific behavioural impairments found in cases of adult brain damage and developmental disorders correspond to similar underlying causes, and can serve as convergent evidence for the modular structure of the normal adult cognitive system. We argue that this correspondence is contingent on an unsupported assumption that atypical development can produce selective deficits while the rest of the system develops normally (Residual Normality), and that this assumption tends to bias data collection in the field. Based on a review of connectionist models of acquired and developmental disorders in the domains of reading and past tense, as well as on new simulations, we explore the computational viability of Residual Normality and the potential role of development in producing behavioural deficits. Simulations demonstrate that damage to a developmental model can produce very different effects depending on whether it occurs prior to or following the training process. Because developmental disorders typically involve damage prior to learning, we conclude that the developmental process is a key component of the explanation of endstate impairments in such disorders. Further simulations demonstrate that in simple connectionist learning systems, the assumption of Residual Normality is undermined by processes of compensation or alteration elsewhere in the system. We outline the precise computational conditions required for Residual Normality to hold in development, and suggest that in many cases it is an unlikely hypothesis. We conclude that in developmental disorders, inferences from behavioural deficits to underlying structure crucially depend on developmental conditions, and that the process of ontogenetic development cannot be ignored in constructing models of developmental disorders.

Cognitive frameworks provide important means for uniting concepts of specificity, cognition, and dynamic change in development. Two points are challenged by evidence from special populations: (1) that boundary constraints such as Residual Normality and a cognitive “endstate” compromise the use of cognitive models; and (2) the developmental process itself automatically rejects either Residual Normality or residual deviance from typical development.

Cognitive developmental disorders cannot be properly understood without due attention to the developmental process, and we commend the authors’simulations in this regard. We note the contribution of these simulations to the nascent field of connectionist modeling of developmental disorders and outline a set of criteria for assessing individual models in the hope of furthering future modeling efforts.

Thomas & Karmiloff-Smith’ (T&K-S’) argument that the Residual Normality assumption is not valid for developmental disorders has implications for models of cognition in schizophrenia, a disorder that may involve a neurodevelopmental pathogenesis. A limiting factor for such theories is the lack of understanding about the nature of the cognitive system (modular components versus global processes). Moreover, it is unclear how the proposal that modularization emerges from developmental processes would change that fundamental question.

Thomas & Karmiloff-Smith (T&K-S) correctly identify Residual Normality (RN) as a critical assumption of some theorising about mental structure within developmental psychology. However, their simulations provide only weak support for the conditions under which RN may occur because they explore closely related architectures that share a learning algorithm. It is suggested that more work is required to establish the limits of RN.