The general objective of this research is to study the neurobiology of language using ASL, a language which displays complex linguistic structure but (unlike spoken language) does so in large part by manipulating spatial relations. Space is used in ASL to encode grammatical relations, discourse relations, and spatial layouts. The investigators plan to explore the properties of each of these uses of space, their interaction, and their neurobiological substrates, using new methods of brain imaging, and language and cognitive probes specially developed for these studies. The studies involve deaf life-long signers who have focal lesions to the left or right hemisphere. The proposal has three foci. (1) Left hemisphere organization for ASL grammar. Having shown in previous work that the core aspects of ASL grammar are predominantly left hemisphere functions, the investigators now focus on the neural organization of ASL within the left hemisphere. The goals are to specify the neural systems and pathways underlying ASL grammar, and to investigate relations between language and nonlanguage aspects of cognition. (2) Right hemisphere organization for spatialized discourse and mapping. Signers with lesions in their right hemispheres have no difficulty with the grammatical aspects of ASL but do often show impairments for extragrammatical functions that involve space. The goal is to investigate selective impairments of specific components of ASL spatialized discourse, and to illuminate the functions of the right hemiphere in processing linguistically-encoded spatial relations. (3) Neural systems underlying sign language. Five fMRI experiments that complement the lesion studies are propose to further probe the basis of sign language structure.
