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MITECS: Modularity and Language

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Modularity and Language
Is language a separate mental faculty? Or is it just part of a monolithic general-purpose cognitive system? The idea that the human mind is composed of distinct faculties was hotly debated in the nineteenth century, and the debate continues today. Genetic disorderssuch as Williams syndrome show that individuals who cannot count to three or solve simple spatial tasks nevertheless develop remarkable language skills that resemble those of a fully fluent and proficient second-language learner (Bellugi et al. 1993; Karmiloff-Smith et al. 1997). The striking disparity in the levels of attainment of Williams syndrome individuals in different cognitive domains clearlyargues for differentiated mental capacities.
Studies of the brain lead to the same conclusion. The left hemisphere of the brain is the language-dominant hemisphere for right-handed individuals. In 1861, Paul BROCA identified the third frontal gyrus of the language-dominant hemisphere as an important language area. Performing autopsies on brain-damaged individuals with expressive difficultiescharacterized by slow, effortful "telegraphic" speech, he found that their lesions involved the third frontal gyrus, now known as "Broca's area." Using modern neuroimaging techniques, Smith and Jonides (1997) have implicated Broca's area specifically in the rehearsal of material in verbal WORKING MEMORY in normal adults, showing an increase in activation with increasing memory load. Spatial tasksrequiring active maintenance of spatial information in working memory do not activate Broca's area in the left hemisphere but rather the premotor cortex of the right hemisphere. Though the overall picture of language representation in the brain is far from clear, the debates today mostly concern, not whether areas specialized for language (or object recognition or spatial relations) exist, but howthese areas are distributed in the brain and organized. In studies of normal adult language processing, modularity is discussed in broad terms where the questions concern the separability of grammatical processing from general cognitive processing and in narrow terms where the questions concern the isolability of distinct components of the grammar. One central question is whether a syntactic parserexists that is concerned only with the construction of syntactic structure in production or the identification of syntactic structure in comprehension. In studies of sentence production, Bock (1989) presents evidence for purely syntactic priming not dependent on semantic content or the particular words in a sentence. In other words, having just produced a sentence with a particular syntacticstructure, speakers tend to use that same structure again even under circumstances where there is no semantic relation between the two sentences. This result is expected if syntax is a specialized component of a modular language processor in the narrow sense. Similarly in comprehension, Clifton (1993) has shown that a phrase following an optionally transitive verb is first analyzed as an object of thatverb even if semantic properties of the clause dictate that ultimately it must be the subject of a following clause. Both studies provide

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10/02/2009 11:57

MITECS: Modularity and Language

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evidence for the existence of autonomous syntactic structures that participate in language processing. Laying out a veryspecific modularity thesis, Fodor (1983) hypothesizes that perceptual, or "input," systems share several important characteristics. They apply only to a limited domain, visual inputs, for example. Only domain-specific information (e.g., visual information) is applied in the input system. The operation of the input system is fast and reflexive (automatic and mandatory). There is limited access to...