| The purpose of this dissertation is to provide an objective test of Lenneberg's Critical Period Hypothesis. The hypothesis is tested by studying the acquisition of sign language by a deaf adult who had not been previously exposed to language.;Both longitudinal and non-longitudinal data are used in this study to test tenets of Lenneberg's hypothesis. The results of the study suggest that the subject has developed considerable language competence. He has demonstrated marked improvement in his ability to respond correctly to yes/no and wh-questions. His performance on comprehension tests improved over time and this suggests his underlying competence has increased. The subject has expressed in his utterances all the semantic relations found in the language of children. Furthermore, his performance on an imitation test revealed the same types of reduction patterns found in child language. Finally, the subject has developed a rudimentary knowledge of Signed English, written English and some basic math skills. These are taken as evidence of cognitive development which is not predictable according to the Critical Period Hypothesis.;On the basis of the results of the study, it would appear that several of the main tenets of Lenneberg's hypothesis are weak. First, it does not seem that cerebral reorganization of function is lost after puberty. Second, there does not appear to be an absolute terminal point with respect to the categorization process after which new conceptual information cannot be learned. Finally, the idea of a structural matrix to account for all language learning after puberty does not seem to be supported by the evidence.;Language acquisition in general is discussed as well as the various models of language which have been proposed to account for the acquisition process. Then, the nature and structure of ASL is discussed in order to isolate the similarities and differences which exist between spoken and gestural languages. The concept of the critical period, its origin and the problems and implications it poses for language acquisition in a visual-gestural modality are also discussed. |
