The question addressed in our study is whether the acquisition of two or more languages can be qualified as an instance of multiple first language acquisition or whether there are qualitative differences between monolingual and multilingual development. Our basic assumption is that the human language faculty is an endowment for multilingualism. The human Language Making Capacity (LMC) is nevertheless subject to maturational changes, i.e. neural maturation opens a window of opportunities for multiple L1 acquisition. However, in the course of further development the LMC becomes partially inaccessible. In order to test these assumptions, we contrast bilingual first language acquisition (2L1) both with monolingual first language acquisition (L1) and with child and adult second language acquisition (L2). The main focus of our analysis is placed on the acquisition of finiteness and the position of the verb, the left periphery, tense and aspect, and clitic pronouns.
More specifically, two hypotheses have been investigated by this research project, namely the Autonomy Hypothesis and the Maturation Hypothesis. The hypothesis of autonomous grammatical development is based on the Critical Period Hypothesis according to which the language capacity can be activated during sensitive phases of cognitive development in which Universal Grammar (UG) becomes accessible; its principles determine the nature of the grammatical system at each stage of language acquisition. The claim here is that both languages in bilingual development will thus develop in the same fashion as in monolingual acquisition. This is the reason why no qualitative differences are expected to emerge in bilingual acquisition, when compared to monolingual development in the respective languages. In other words, no cross-linguistic influences between the grammars of the two languages are expected to happen. We analyzed the language production of French-German, Spanish-Basque, and Portuguese-German bilinguals. The results obtained so far in our comparison of 2L1 with monolingual L1 acquisition confirm these predictions. The linguistic systems of the two languages are differentiated form early on and grammatical development proceeds through the same developmental sequences as in monolingual acquisition.
In order to put our hypotheses to a test, we place special focus on the grammatical development of unbalanced bilingual children. The question in this context is whether the same conclusions are warranted in cases in which one of the languages appears to be significantly weaker than the other. Our results suggest that the rate of development may be delayed, in some cases quite significantly, but that qualitative differences do not arise. Our preliminary conclusion is therefore that the Autonomy Hypothesis is indeed correct. Currently, we are further exploring these claims, by means of analyzing apparently vulnerable domains in the grammars of the structurally distinct and genetically unrelated languages Basque and Spanish.
The Maturation Hypothesis is derived from the assumption that access to the LMC is developmentally limited, i.e. it is no longer directly accessible in second language acquisition. In order to test this hypothesis we compare bilingual and monolingual L1 development with child and adult L2 acquisition. Our preliminary results confirm the claim that successive acquisition of two or more languages differs substantially from both monolingual and bilingual first language acquisition. Language acquisition is, of course, still possible, but L2 learners have to resort to other cognitive capacities in order to compensate for those which are no longer available. Based on previous results both from linguistic and neurological studies, our assumption is that the optimal period for grammatical acquisition begins to fade out as early as the age of 3 or 4, i.e. considerably earlier than generally assumed. Further major changes in the LMC seem to occur around the age of 8. We therefore distinguish between (2) L1 (age of onset before or at the age of 3 to 4), child L2 (age of onset during the age period ranging from approximately age 4 through 8), and adult L2 acquisition (age of onset at around 8 or later).
The aim of our current research is to determine which features are shared by cL2 and aL2, distinguishing both from L1, and which linguistic properties cL2 shares with (2) L1 but not with adult L2. Our hypothesis is that child L2 resembles adult L2 in crucial aspects of grammatical development, particularly in the domain of grammatical morphemes and possibly also in some areas of syntax. These claims are currently being put to a test in a study with German children acquiring French as of age 3.
In order to corroborate the results obtained by linguistic analyses on learners´ language use, we have conducted a fmRI study in collaboration with a research group at the Institut für Systemische Neurowissenschaften Universitätsklinikum Hamburg-Eppendorf (http://www.uke.uni-hamburg.de/institute/systemische-neurowissenschaften) comparing 2L1 subjects who acquired French and German simultaneously to highly proficient French L2 learners of German and German L2 learners of French. Our results suggest that syntactic processing in the second language causes a stronger activation in the typical areas of the brain
the L1. Since no such effect can be found in early bilinguals,
one can argue that the age of onset of acquisition causes these differences.