PARAMETER SETTING: EVIDENCE FROM USE, ACQUISITION, AND BREAKDOWN IN AMERICAN SIGN LANGUAGE (NULL ARGUMENTS, APHASIA, SYNTAX)

In American Sign Language, null arguments (phonologically non-overt subjects and objects) can appear freely with verbs which take agreement, and to a limited extent with verbs which do not take agreement. The null arguments which appear with agreement are analyzed as pro, and with this class of verbs ASL can be analyzed similarly to many null argument languages, such as Irish and Italian. However, the null arguments which appear without agreement are more like the null arguments found in Chinese and Japanese, in their distribution and behavior. These null arguments are analyzed as variables coindexed with a null topic. Thus, two types of null arguments are found in one language.; The acquisition of these two types of null arguments was also studied, in production, imitation, and comprehension tests. It was found that complete competence with the null arguments of agreeing verbs was not attained until relatively late, 5-6 years of age. However, it was argued that this lateness reflects not a lateness in the correct setting of the Null Argument Parameters, but interference from the acquisition of the complex morphology involved in the verb agreement system. Since aspects of the complex verb morphology are not acquired until 5-6 years, an overt manifestation of the correct setting on the Null Argument Parameter is not possible until this time.; Furthermore, studies of adult deaf aphasic patients also support the above analysis of null arguments as dependent on agreement. One aphasic patient often failed to use agreement, and likewise did not use the null arguments which are sanctioned by agreement, although he did use the second type of null argument. Another aphasic patient used the verb agreement system well, and used null arguments with verb agreement; however, she often had problems specifying the reference of overt and null pronominals.; This study, encompassing theoretical linguistics, psycholinguistics, and neurolinguistics, brings cross-disciplinary support to an analysis of ASL within the proposals for Universal Grammar containing language-independent principles along with language-particular parameters.