Dissociating neural subsystems for grammar by contrasting word order and inflection

Abstract

An important question in understanding language processing is whether there are distinct neural mechanisms for processing specific types of grammatical structure, such as syntax versus morphology, and, if so, what the basis of the specialization might be. However, this question is difficult to study: A given language typically conveys its grammatical information in one way (e.g., English marks "who did what to whom" using word order, and German uses inflectional morphology). American Sign Language permits either device, enabling a direct within-language comparison. During functional (f)MRI, native signers viewed sentences that used only word order and sentences that included inflectional morphology. The two sentence types activated an overlapping network of brain regions, but with differential patterns. Word order sentences activated left-lateralized areas involved in working memory and lexical access, including the dorsolateral prefrontal cortex, the inferior frontal gyrus, the inferior parietal lobe, and the middle temporal gyrus. In contrast, inflectional morphology sentences activated areas involved in building and analyzing combinatorial structure, including bilateral inferior frontal and anterior temporal regions as well as the basal ganglia and medial temporal/limbic areas. These findings suggest that for a given linguistic function, neural recruitment may depend upon on the cognitive resources required to process specific types of linguistic cues.brain | language | sign language | syntax | neuroimaging D espite the great diversity of human languages, the neural basis of language processing has been documented in only a very few languages. To the extent that the neural underpinnings of language are truly universal, the available research may reflect quite accurately what would be found across languages. Alternatively, the fact that the grammars of different languages encode information in different ways may place different processing demands on the neurocognitive systems supporting language (1). For example, in English the order of the words in the sentence John gave his lunch to Mary encodes the grammatical "dependency relationships"-essentially, who did what to whom. Ordering the words differently would convey a different meaning or no meaning at all. In other languages such as German or American Sign Language, word order is less restricted because dependency relationships can be marked by other cues, such as tagging words with inflectional morphemes (e.g., in German, suffixes are added to words within the noun phrase to mark the noun's "case" or role in the sentence, e.g., as "doer" or "receiver" of an action). Whether these different strategies for encoding grammatical information rely on a unitary network of brain regions specialized for processing "grammar" in a broad sense, or whether they impose distinct processing demands relying on nonidentical neural mechanisms, is a fundamental question. It has implications for our understanding of the neurocognition of language, for its relationship to other ...

Neural systems supporting linguistic structure, linguistic experience, and symbolic communication in sign language and gesture

“…An extensive portion of the right anterior/middle STS was also activated exclusively in signers. This region showed no specialization for linguistically structured material, although in previous studies we found sensitivity of this area to both morphological and narrative/prosodic structure in ASL (17,18). It thus seems that knowledge of a visual-manual sign language can lead to this region's becoming more sensitive to manual movements that have symbolic content, whether linguistic or not, and that activation in this region increases with the amount of information that needs to be integrated to derive meaning.…”

“…Our data revealed that, when sign language and gesture stimuli are closely matched for content, and once perceptual contributions are properly accounted for, a much more restricted set of brain regions are commonly engaged across stimulus types and groupsrestricted to middle and anterior regions of the right STS. We have consistently observed activation in this anterior/middle right STS area in our previous studies of sign language processing, in both hearing native signers and late learners (16) and in deaf native signers both for ASL sentences with complex morphology [including spatial morphology (18), and narrative and prosodic markers (17)]. The present findings extend this to nonlinguistic stimuli in nonsigners, suggesting that the right anterior STS is involved in the comprehension of symbolic manual communication regardless of linguistic structure or sign language experience.…”

“…This includes the inferior frontal gyrus (IFG) (classically called Broca's area), superior temporal sulcus (STS) and adjacent superior and middle temporal gyri, and the inferior parietal lobe (IPL) (classically called Wernicke's area) including the angular (AG) and supramarginal gyri (SMG) (4,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Likewise, narrative and discourse-level aspects of signed language depend largely on right STS regions, as they do for spoken language (17,19).…”

Visual cortex entrains to sign language

“…Across signed and spoken language, bloodflow increases to the left inferior frontal gyrus (LIFG) and left inferior parietal lobe (IPL) during phonemic discrimination (49,50) and morphosyntactic processing (51). Similarly, word production in both signed and spoken languages activates LIFG, left IPL, and left temporal areas (52).…”

Syntactic diacrisis in a rigid and a free word order language

“…Some indirect support for this last claim seems to come from research on the neural basis of processing. Newman et al (2010) found out in a series of neuroimagining experiments that processing constructions in a language like English that "typically conveys grammatical information…. using word order" (positional languages in our terminology) activated "left-lateralized areas involved in working memory and lexical access" while "inflectional morphology sentences activated areas involved in building and analyzing combinatorial structure".…”