An investigation of the effects of proficiency and age of acquisition on neural organization for syntactic processing using ERPs and fMRI
Pakulak, Eric Robert
Improvements in neuroimaging techniques have made it possible to answer questions regarding the neural organization for the processing of syntax in normal participants. In this series of experiments we examined the effects of linguistic proficiency and age of second language acquisition on neural organization for syntactic processing. We examined these factors using two complementary methodologies: event-related potentials (ERPs), which affords a temporal resolution on the order of milliseconds, and functional magnetic resonance imaging (fMRI), with spatial resolution on the order of millimeters. In order to compare results across methodologies, we used an auditory syntactic violation paradigm with similar experimental parameters in each methodology. In Chapter II we examined neural organization for syntactic processing using ERPs in monolingual native speakers of higher and lower proficiency and found that violations elicited an early onset (100 ms) anterior negativity (EOAN) followed by a later positivity (P600) in all participants. Compared to lower proficiency participants, higher proficiency participants showed an EOAN that was more focal spatially and temporally, and showed a larger P600. These results were supported by a correlational analysis of a larger group of monolingual native speakers with a wide range of proficiency scores. This analysis also found a relationship between childhood socioeconomic status and the recruitment of the EOAN over left hemisphere sites, raising the hypothesis that effects of childhood experience may endure into adulthood. In Chapter III we examined the effects of age of acquisition on syntactic processing by recruiting a group of late learners of English who were matched for proficiency with a group of monolingual native speakers from Chapter II. While in native speakers violations elicited a robust EOAN, this effect was absent in the late learner group, suggesting that early language exposure is important for the recruitment of resources reflected in this effect and independently of proficiency. In Chapter IV we gathered ERP and fMRI data from monolingual native speakers and found proficiency differences in the recruitment for syntactic processing of left inferior frontal and posterior regions. We linked proficiency-related modulations in the different ERP syntactic effects to specific fMRI activations indexing syntactic processing.