The Interface Hypothesis (Sorace and Filiaci, 2006) conjectures that adult second language learners (L2 learners) who have reached near-native levels of proficiency in their second language exhibit difficulties at the interface between syntax and other cognitive domains, most notably at the syntax-discourse interface. However, research in this area was limited, in that the data were offline, and thus unable to provide evidence for the nature of the deficit shown by L2 learners. This thesis presents online data which address the question of the underlying nature of the difficulties observed in L2 learners at the syntaxdiscourse interface. This thesis has extended work on the syntax-discourse interface in L2 learners by investigating the acquisition of two phenomena at the syntax-discourse interface in German: the role of word order and pronominalization with respect to information structure (Experiments 1-3), and the antecedent preferences of anaphoric demonstrative (the der, die, das series homophonous with the definite article) and personal pronouns (the er, sie, es series) (Experiments 4- 8). Crucially, this work has used an on-line methodology, the visual-world paradigm, which allows an insight into the incremental interpretation of interface phenomena in real-time processing. The data from these experiments show that L2 learners have difficulty integrating different sources of information in real-time comprehension efficiently, supporting the Interface Hypothesis. However, the nature of the processing difficulties which L2 learners demonstrate in on-line processing was not determined by these studies, resulting in the question: are L2 learners’ difficulties a result of a limitation of processing resources, or the inability to deploy those resources effectively? A novel dualtask experiment (Experiment 9), in which native speakers of German were placed under processing load simulated the results previously obtained for L2 learners. It is concluded that syntactic dependencies were constrained by resource limitation, whereas discourse based dependencies were constrained by processing resource allocation.

This thesis focuses on the cross-linguistic differences between Italian and Spanish regarding the pragmatic restrictions on the resolution of null and overt subject pronouns (NS and OSP). It also tries to identify possible links between such cross-linguistic differences and morpho-syntactic differences at the level of the verbal morphology of the two languages. Spanish and Italian are typologically related and morpho-syntactically similar and have been assumed to instantiate the same setting of the NS parameter with respect to not only its syntactic licensing conditions, but also the pragmatic constraints determining the distribution of null and overt subject pronouns, and this assumption has had important implications for cross-linguistic research. The first aim of this study was to test directly for the first time the assumption about the equivalence of Italian and Spanish; in order to do so, I run a series of self-paced reading experiments using the same materials translated in each language, so that the results were directly comparable. The experiments were based on Carminati’s (2002) study on antecedent preferences for Italian NSs and OSPs in intra-sentential anaphora, testing the Position of Antecedent Strategy. The results suggest that while in Italian there is a strict division of labour between NS and OSP (confirming Carminati’s findings), this division is not as clear-cut in Spanish. More precisely, while Italian personal pronouns unambiguously signal a switch in subject reference, the association between OSPs and switch reference seems to be much weaker in Spanish. These results, which are interpreted in terms of Cardinaletti and Starke’s (1999) cross-linguistic typology of deficient pronouns, highlight an asymmetry between the strength of NS and OSP biases in Spanish that could not have emerged through the traditional methodology used by the numerous variationist studies on the subject, based on corpus analysis. A subsequent pair of experiments tested the hypothesis that the cross-linguistic differences attested might be related to the relative syncretism of the Spanish verbal morphology compared to the Italian one with regard to the unambiguous expression of person features on the verbal head. The results only provided weak support for the hypothesis, although they did confirm the presence of the cross- linguistic differences in the processing and resolution of anaphoric NS and OSP dependencies revealed by the previous experiments.

It has long been theorized that, after the so-called critical period has passed, acquiring language becomes a more difficult enterprise. While general differences between adult second language (L2) learners and normally developed child (L1) acquirers have been more or less empirically established, a strand of recent L2 accounts have focused on the specific locus of these differences. The main goal of this dissertation project is to test the predictions of one such account: Clahsen and Felser's Shallow Structure Hypothesis (SSH; Clahsen & Felser 2006a, 2006b). The SSH places emphasis on the empirical testing of native/non-native language processing asymmetries, which are argued to be due to less detailed L2 grammatical representations. This dissertation tests the predictions of the SSH using a long-distance dependency: Clitic Left Dislocation (CLLD) in L2 Spanish. The study includes on-line and an off-line tasks, which were completed by a control group of native speakers of Spanish and an experimental group constituted by L2 learners of Spanish whose first language was English. In view of the well-known fact that L2 learning outcomes vary widely across individuals, a secondary goal of this dissertation project is to determine whether variability in individual learning abilities, such as inhibitory control and statistical learning predicts variability in L2 learning. Part of L2 learning involves detecting the probabilistic patterns of a language (Saffran, Aslin, & Newport, 1996), such that individuals who are better pattern learners may be better able to learn the structural regularities of the L2 input. Results were analyzed in order to determine whether the predictions of the SSH could account for the patterns present in the data. These results suggest that although the acquisition of long-distance dependencies is a protracted process, both intermediate and advanced L2 learners of Spanish could anticipate (predict) a syntactic element based in previously occurring cues. Thus, these results fail to support the predictions of the SSH. In terms of individual differences, overall, neither statistical learning nor inhibitory control appear to modulate the on-line processing of this particular long-distance dependency in Spanish.