This thesis has been undertaken with the purpose of investigating how adult speech processing systems are affected by. and how they cope with, the presence of different regional and foreign accents in speech, and to investigate the developmental origins of adult accent perception capabilities. Experiments 1 to 4 were designed to investigate the long term effects of exposure to different accents, and whether short term adaptation to an accent was possible, using a lexical decision task. The results demonstrated an effect of accent familiarity but no short term adaptation was evident. Experiments 5 to 7 investigated the short term effects of accents by looking at the length of activation of accent-related information in working memory by using a cross-modal matching task. The results found that selective accent related effects were reduced after a 1500 millisecond delay. Experiments 8 to 11 investigated infants' discrimination abilities for regional and foreign accents using a preferential looking habituation method, and found infants at 5 and 7 months could discriminate their own accent from another, unfamiliar regional accent, but could not discriminate two unfamiliar regional accents at 5 months or a foreign accent from their own at 7 months. Experiments 12 and 13 investigated how accents affected infants' word segmentation abilities with continuous speech at 10 months, and found that segmentation was impaired in the presence of regional and foreign accents. Using these results, the Accent Training Model (ATP) is proposed, which attempts to explain how accent related indexical information is processed in the speech processing system. The findings of the infant studies further our understanding of the effect of indexicat variation in early speech perception.

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