The general objective of our research is to study the neurobiology of language. American Sign Language (ASL) displays complex linguistic structure, but unlike spoken language conveys much of its structure by manipulating spatial relations. Space is used in ASL in a multifunctional way: (l) to encode grammatical relations within individual signs (phonology & morphology) and among those signs within a sentence (syntax); (2) to encode discourse relations among the referents in a discourse across sentences; and (3) to encode spatial relations themselves in the context of describing spatial layouts. We propose to explore the properties of each of these uses of space in ASL, their interaction, how they relate to non-linguistic spatial cognition, and their underlying neurobiology. Left Hemisphere Organization for ASL Grammar. Our research strongly supports a linguistic basis for the left hemisphere specialization for language. In the renewal, we investigate the neural organization of sign language within the left hemisphere. We propose new experiments designed to elucidate the ways in which various grammatical components of ASL break down following brain damage, with emphasis on the unique encoding of grammatical information in ASL (e.g. via facial expression & spatial contrasts). Right Hemisphere Organization for ASL Spatial Discourse. ASL discourse representations are encoded in space, and discourse functions are achieved by manipulations of spatial-discourse frameworks. RHD signers show no signs of aphasia but frequently show impairments at the discourse level. We will use a new tasks to follow up on evidence for a selective impairment of specific components of sign discourse. The Use of Space to Represent Spatial Relations in ASL. Besides using space to represent grammatical and discourse relations, ASL uses space to represent spatial relations themselves. In spatial mapping, the spatial relations among points in signing space map onto real-world spatial relations in an isomorphic fashion. We will investigate the basis of RHD deficit in this area, which contrasts with RHD subjects' unimpaired usage of space for syntactic functions. Brain Organization for Spatial Cognition. We will study the relation between various spatial cognitive functions and the use of space in ASL (discourse & spatial mapping). We will also investigate mental imagery in signers, following up on preliminary indications that signers may show enhancement of specific facets of image manipulation. We will compare performance in deaf signers with hearing non-signers to probe effects of linguistic experience on brain organization for spatial cognition. The Neural Systems Underlying Sign Language: Modality Dependent and Independent Effects. Using a recent dramatic improvement in neuroimaging (BrainVox) that allows 3-D in vivo visualization of brains, we initiate a new program aimed at mapping out the neural systems underlying ASL processing, bearing directly on the issue of neuronal plasticity and the effects of linguistic experience on brain organization.
