Second language acquisition (SLA) has been a dominant field in linguistics research over the past several decades. In this field, researchers have investigated what makes learning the grammar of a second language difficult and they have identified many factors that may contribute to this difficulty, including agreement processing. In linguistic terms, agreement refers to the necessary covariation of grammatical features between two of more syntactic constituents. In prior years of agreement processing research, some authors examined how native speakers process varying grammatical features (e.g. number and gender) in agreement relations. In recent years, however, they have turned towards L2 learners and have investigated whether learners can attain native-like levels of processing agreement in a second language.While some researchers have investigated differences between learners and native speakers, others have examined the effect of individual differences on agreement processing. Of particular interest to this thesis is working memory capacity (WMC) and its effect during the different processing stages of agreement. Lastly, features expressed through agreement may affect individuals' processing behavior. Different features (e.g. person, number, gender) are regularly expressed in agreement relations by different manifestations of exponence. Many authors have investigated the effect different features have on processing agreement when those features are expressed by separative exponence. Fewer have examined the effect of cumulative exponence on agreement processing.Eye tracking is a useful psycholinguistic tool to investigate these questions. Using eye tracking, I examine English learners of Spanish and their eye behavior as they processed Spanish verbal agreement and investigate whether they demonstrate sensitivity similar to native Spanish speakers while processing verbal agreement errors. I investigate if individuals demonstrate similar sensitivity when processing three different types of verbal agreement errors—number, person, and tense. Additionally, I examine whether individuals' sensitivity to agreement errors is affected by working memory capacity. Using a linear mixed effects model, I analyze the eye tracking data and share the results of the analyses and their implications for L2 research in agreement processing.

The present dissertation investigates grammatical gender representation and processing in Modern Standard Arabic (MSA) as a first (L1) and a second (L2) language. It mainly examines whether L2 can process gender agreement in a native-like manner, and the extent to which L2 processing is influenced by the properties of the L2 speakers’ L1. Additionally, it examines whether L2 gender agreement processing is influenced by noun animacy (animate and inanimate) and word order (verb-subject and subject-verb). A series of experiments using both online and offline techniques were conducted to address these questions. In all of the experiments, gender agreement between verb and nouns was examined. The first series of experiments examined native speakers of MSA (n=49) using a self-paced reading task (SPR), an event-related potential (ERP) experiment, and a grammaticality judgment (GJ) task. Results of these experiments revealed that native speakers were sensitive to grammatical violations. Native speakers showed longer reaction times (RT) in the SPR task, and a P600 effect in the ERP, in responses to sentences with mismatched gender agreement as compared to sentences with matched gender agreement. They also performed at ceiling in the GJ task. The second series of experiments examined L2 speakers of MSA (n=74) using an SPR task, and a GJ task. Both experiments included adult L2 speakers whom were divided into two subgroups, -Gender and +Gender, based on whether or not their L1s has a grammatical gender system. The results of both experiments revealed that both groups were sensitive to gender agreement violations. The L2 speakers showed longer RTs, in the SPR task, in responses to sentences with mismatched gender agreement as compared to sentences with matched gender agreement. No difference was found between the L2 groups in this task. The L2 speakers also performed well in the GJ task, as they were able to correctly identify the grammatical and ungrammatical sentences. Interestingly in this task, the -Gender group outperformed +Gender group, which could be due to proficiency in the L2 as the former group obtained a better score on the proficiency task, or it could be that +Gender group showed negative transfer from their L1s. Based on the results of these two experiments, this dissertation argues that late L2 speakers are not restricted to their L1 grammar, and thus, they are able to acquire gender agreement system of their L2 even if this feature is not instantiated in their L1. The results provide converging evidence for the FTFA rather than FFFH model, as it appears that the -Gender group was able to reset their L1 gender parameter according to the L2 gender values. Although the L2 speakers were advanced, they showed slower RTs than the native speakers in the SPR task, and lower accuracy in the GJT. However, it is possible that they are still in the process of acquiring gender agreement of MSA and have not reached their final stage of acquisition. This is supported by the fact that some L2 speakers from both -Gender and +Gender groups performed as well as native speakers in both SPR and GJ tasks. Regarding the effect of animacy, the L2 speakers had slower RT and lower accuracy on sentences with inanimate nouns than on those with animate ones, which is in line with previous L2 studies (Anton-Medez, 1999; Alarcón, 2009; Gelin, & Bugaiska, 2014). The native speakers, on the other hand, showed no effect of animacy in both SPR task and GJT. Further, no N400 effect was observed as a result of semantic gender agreement violations in the ERP experiment. Finally, the results revealed a potential effect of word order. Both the native and L2 speakers showed longer RTs on VS word order than SV word order in the SPR task. Further the native speakers showed earlier and greater P600 effect on VS word order than SV word order in the ERP. This result suggests that processing gender agreement violation is more complex in the VS word order than in the SV word order due to the inherent asymmetry in the subject-verb agreement system in the two-word orders in MSA.