The influence of phonetic experience on perceptual flexibility and auditory plasticity in bilinguals



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The goal of this dissertation was a) to investigate how phonetic experience in two languages influences the perception of novel speech sounds and b) reveal the underlying neural mechanisms involved in novel speech learning. Adult English monolinguals (n = 20) and early Spanish-English bilinguals (n = 24) participated in four consecutive sessions of phonetic discrimination training (same vs. different) while listening to Hungarian non-words that contained the novel speech phonemes /ø/, /ø:/, /u:/, /u/, /o:/, /y/, /y:/, /o/. Participants completed two fMRI sessions, one before training and the other after training. The in-scanner task consisted of passively listening to the novel speech stimuli with which participants trained outside the scanner. The behavioral results indicated that monolinguals and bilinguals both learned after training, and discrimination of novel speech did not differ between groups. Nonetheless, the neural processes engaged by monolinguals and bilinguals differed after training (left anterior cingulate gyrus in monolinguals and bilateral parietal regions in bilinguals). A separate post-hoc regression analysis examined how participants’ overall discrimination performance predicted brain activity before and after training. Here it was found that better perceivers were more likely to recruit sensory-perceptual areas (bilateral superior temporal gyrus and cerebellar vermis), whereas worse perceivers were more likely to recruit higher-order cognitive areas after training (right postcentral gyrus, superior parietal lobule, and left supramarginal gyrus). These findings suggest that growing up in bilingual phonetic environments does not facilitate novel speech learning. Instead, the ability to discriminate novel speech appears to originate from individual enhanced perceptual abilities present prior to training.



Perception, Learning, Neurosciences, Bilingualism