Perceptual Learning of Accented Speech by First and Second Language Listeners

This dissertation explores the processes that drive perceptual adaptation to variation in speech by examining how sources of prediction and uncertainty modulate perceptual learning processes. In particular, we examined how the perceptual system leverages different types of information during adaptation, varying in the degree to which they predict the relevant phonemic categories in the speech input, and how linguistic experience mediates this process.;In Study 1, we examined the relative contribution of different levels of linguistic information (e.g., phonemic, lexical, prosodic) by presenting listeners with Mandarin-accented English sentences followed by native-accented feedback that aligned with the target to varying degrees. Listeners provided with any kind of native English-accented feedback (matched or mismatched sentences) significantly outperformed those who were not presented with this kind of feedback, suggesting that listeners drew upon points of alignment between the native- and Mandarin-accented sentences beyond the lexical and that the perceptual system will leverage any linguistically-relevant information during adaptation, even if it is not highly predictive of the input.;Study 2 compared the contribution and interaction of different types of information, namely linguistic knowledge (lexical vs. semantic context) and signal-based information (single vs. multi-talker training) during exposure to a novel English accent. Additionally, the impact of uncertainty during adaptation was also explored by comparing first (L1) and second (L2) language listeners, who vary in the amount of linguistic uncertainty they maintain about the target language. Significant adaptation found by both L1 and L2 listeners highlight the remarkable flexibility and efficiency of the perceptual learning system, capable of leveraging any relevant information available in the context, regardless of its predictive strength. Moreover, linguistic experience was found to play a dynamic role in adaptation, demonstrating a combination of plasticity and stability within the system as a function of the type of phonemic contrast employed in the accent pattern. These results point to perceptual adaptation involving a dynamic interaction of prior knowledge and uncertainty with current beliefs about the observed auditory input.