Implicit and Explicit Neural Mechanisms Supporting Language Processing
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Despite the enormous complexity inherent to language, almost all humans acquire and use their native language with apparent effortlessness, simply from being immersed in a normal social environment. It has been hypothesized that conscious processes play only a limited role in language, which may explain how language can be acquired and processed with so little effort. Using event-related potentials, this dissertation addresses this hypothesis by investigating the contributions of implicit and explicit neural mechanisms to different aspects of language. In the first study, the neural mechanisms mediating semantic and syntactic processing of word pairs were examined, using the attentional blink (AB) to manipulate awareness of target words. In the semantic condition, correctly reported target words elicited an N400 effect, while missed target words did not elicit an N400. These results provide evidence that awareness plays a critical role in semantic processing. In the second study, the neural mechanisms that support syntactic processing of full sentences were investigated, using a cross-modal AB to manipulate awareness of syntactic violations. Syntactic violations that were not consciously detected nonetheless elicited a left anterior negativity, indicating that syntactic processing is subserved by implicit neural mechanisms. In the third study, the neural mechanisms underlying semantic acquisition were examined, using a task in which the meanings of novel pseudowords were learned through context. Novel pseudowords elicited a robust N400 effect after remarkably little exposure but only during an explicit task and only when word meanings could be explicitly recognized, indicating that vocabulary acquisition is primarily mediated by explicit neural mechanisms. In the fourth study, the neural mechanisms that support the acquisition of second language (L2) syntax were investigated, using a language-learning task in which participants were trained either implicitly or explicitly. Regardless of training condition, learners who successfully learned the novel L2 syntactic rules showed P600 effects, suggesting that explicit mechanisms play a crucial role in acquiring L2 syntax. Taken together, results from these studies suggest that awareness plays a critical yet constrained role in language processing, yielding new insight into how language is spoken and understood so effortlessly. This dissertation includes previously published and co-authored material.