EPIGENESIS OF LANGUAGE

(S)tudies employing event-related brain potentials (ERPs) and function al magnetic resonance imaging (fMRI) were designed to study the effect s of different types of language experience on the development and org anization of neural systems important in language processing. Comparis ons of cerebral organization in normally hearing, monolingual English speakers with that observed in hearing and deaf late learners of Engli sh suggest that while systems important in lexical/semantic processing are relatively invulnerable to delays in exposure to a language, the development of systems important in grammatical processing, including the specialization of the left hemisphere, is affected by early langua ge experience. Studies of individuals who acquired American Sign Langu age (ASL) as a native language suggest that similar systems within the left hemisphere are employed in processing all natural languages inde pendently of the structure and modality of the language acquired. Thes e studies also reveal that additional areas within the right hemispher e can be recruited into the language system when the language depends on the perception of spatial location and motion. Studies of children acquiring their first language reveal that there is increasing differe ntiation of the neural systems important in processing the meaning of words and of the areas important in lexical and grammatical processing and that these increases in specialization are linked to language abi lities rather than to chronological age per se. Further studies sugges t that developmental language impairment can result from alterations i n one of several different systems important in language, and that som e indices of these functional neural systems may be predictive of lang uage impairment. (C) 1997 Wiley-Liss, Inc.