This thesis explores the role of age in second language (L2) acquisition and first language (L1) attrition. The focus is on Voice Onset Time (VOT) in the production and categorical perception of word-initial L1 and L2 stops in highly advanced L1 Spanish learners of L2 Swedish. Using as the point of departure a maturational constraints perspective and the Critical Period Hypothesis (CPH), Study I examines the impact of age of onset (AO) of L2 acquisition on the production of L2 Swedish voiceless stops. The results show that there are AO effects even in the speech of highly advanced L2 learners and that the incidence of nativelike L2 learners is considerably lower than earlier assumed. However, conclusions like these are only possible when speaking rate is accounted for, thereby highlighting the importance of speaking rate effects on VOT as a measure of nativelikeness. Like Study I, Study II reveals age effects on the same L2 learners’ categorical perceptions of L2 Swedish stops. Moreover, after combining the results with the data from Study I, the incidence of nativelike behavior drops remarkably with no late L2 learner performing within the range of native-speaker production and perception. The results suggest that L2 acquisition of phonetic/phonological aspects is especially sensitive to AO effects. It is concluded that theories on maturational constraints, including the CPH, cannot be refuted on the basis of the present data. Study III concerns the same participants’ production and perception of L1 Spanish stops. Age of reduced contact (ARC) is identified as an important predictor for L1 attrition and retention of voiceless stop production, although not of stop perception. This discrepancy is related to different activation thresholds as proposed by the Activation Threshold Hypothesis (ATH). It is further suggested that early bilinguals are more dependent on high-frequency L1 use than late bilinguals when compensating for age effects, but only in production. / <p>At the time of doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Accepted. Paper 2: In press. Paper 3: Manuscript.</p> / Age of onset and ultimate attainment in second language acquisition, The Bank of Sweden Tercentenary Foundation, grant no. 1999-0383:01 / First language attrition in advanced second language speakers, Swedish Research Council, grant no. 421-2004-1975

The nature of the bilingual mental lexicon and how the L1 and the L2 interact in language production and processing has been the focus of decades of research from linguistic, psycholinguistic and neurolinguistic perspectives. In spite of this significant body of evidence, the degree to which the L1 influences L2 production and processing remains an area of debate, especially with respect to formal features such as grammatical gender. While it is clear that non-nativelike production and processing of L2 grammatical gender persist even in highly-proficient adult bilinguals, the underlying representation of the L1 and L2 gender features and how this representation affects the use of gender in the L2 is currently unclear. Furthermore, there is no evidence at present regarding the nature of the L1-L2 grammatical gender system when the L1 and the L2 have asymmetric gender systems (in other words, differ in number of gender values), as is the case with German, which bears three gender values (masculine, feminine and neuter), and Spanish and French, which each display two gender values (masculine and feminine). This dissertation investigates the representation of and interactions between the L1 and the L2 at the level of the formal gender feature, with a particular focus on language pairings with asymmetric gender systems. Through complementary data from L2 production and processing, I examine the representation of the asymmetric grammatical gender systems in the mental lexicon of L1 Spanish-L2 German and L1 French-L2 German bilinguals and the consequences this asymmetry between the L1 and L2 gender systems has on gender use strategies in the L2. From the perspective of bilingual lexical access, this research contributes new evidence to inform existing psycholinguistic theories of L1-L2 gender interactions and also proposes the Asymmetric gender representation hypothesis, a new model to account for the unique integrated nature of the gender system in bilinguals with L1-L2 asymmetric gender systems. From a language acquisition perspective, the present study provides new data on L2 gender use strategies with asymmetric gender systems, formulating the L1 transfer continuum, which extends existing proposals to include the degree of (a)symmetry between the L1 and the L2. This research also connects theoretical proposals regarding gender agreement in functional-lexical code-switches (specifically, switches within the Determiner Phrase such as dieGER-F mesaSPA-F or elSPA-M TischGER-M) to bilinguals’ preferences in code-switching between two languages that display formal gender. Taken together, all of these complementary perspectives addressed in this dissertation offer a well-rounded perspective of grammatical gender in asymmetric gender systems specifically, and contribute novel evidence regarding the interactions between the L1 and the L2 in the bilingual mental lexicon in general.