Effect of age of first exposure to L2 on L2 contextual lexical semantic learning : evidence from event-related potentials

Abstract

This research aims to study the influence of age of first exposure (AoFE) to L2 on the process of integrating novel words into both episodic and semantic memory systems during multi-contextual learning. To achieve this, we conducted three different but related studies. Eighty-eight participants were recruited to participate in the experiment. They were presented with multi-contextual discourses to learn L2 novel concepts and were tested with three types of discourses or sentences while their EEGs were recorded. These discourses or sentences were designed to be congruous or incongruous by putting different novel words in the final position for participants to make judgments. Study 1 aims to explore the neural mechanism of learning L2 unknown concepts under various contexts and figure out the roles played by different types of memory and semantic relations in this process. We used the N400 component from event-related potentials (ERPs) as a neural indicator of the learning performance for the novel words. N400 is elicited by the incongruency between a target word and its contextual discourse and is assumed to be stronger for better-learned words. It was found that a significant N400 effect was generated when participants were tested on the same (recurrent) materials and new materials with new themes, but not on new materials with new category descriptions. These results showed that multi-contextual learning can effectively support the formation of episodic memory, as well as semantic memory through the establishment of thematic relations. Study 2 focuses on the main issue of this thesis: examining the AoFE effect on the novel concepts’ acquisition. To control various confounding factors, participants’ information closely related to their L2 learning was collected, including their L2 proficiency, working memory capacity, amount of total exposure (AoTE), gender, L2 learning personality, and socioeconomic status (SES). Multiple regression models were adopted to analyze the effect of individual differences on N400 amplitudes elicited by different types of discourses and sentences. It was found that AoFE has a positive effect on the N400 in both recurrence type and new-theme type discourses, which demonstrated the advantages of early learners in the integration of L2 unknown concepts into both episodic and semantic memory. The effect on semantic memory was mainly achieved by the establishment of thematic linkage in the semantic network. Besides, the positive effects of participants’ AoTE, L2 proficiency, and L2 learning personality have also been confirmed by Study 2. Study 3 further investigates the gender difference in the process of absorbing L2 unknown concepts into the memory systems. The analysis of the variance of two-factor mixed design was conducted in this study. The N400 amplitudes elicited by female group and male group in three types of discourses and sentences were separately analyzed. The results show that females are advantageous in processing episodic information, which can be reflected in the significant N400 effect in recurrence type and new-theme type discourses, and males showed stronger neural activity in the generalization and categorization of concepts, which is shown in their stronger N400 effect in category-feature sentences.