Prominent views in second language acquisition suggest that the age of L2 learning is inversely correlated with native-like pronunciation (Scovel, 1988; Birdsong, 1999). The relationship has been defined in terms of the Critical Period Hypothesis, whereby various aspects of neural cognition simultaneously occur near the onset of puberty, thus inhibiting L2 phonological acquisition. The current study tests this claim of a chronological decline in pronunciation aptitude through the examination of a key trait of American English – reduced vowels, or “schwas.” Groups of monolingual, early bilingual, and late bilingual participants were directly compared across a variety of environments phonologically conditioned for vowel reduction. Results indicate that late bilinguals have greater degrees of difficulty in producing schwas, as expected. Results further suggest that the degree of differentiation between schwa is larger than previously identified and that these subtle differences may likely be a contributive factor to the perception of a foreign accent in bilingual speakers.

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Acoustic and articulatory speech perception theories are proposed to explain how listeners map acoustic signals to phonetic categories. Different from acoustic theories, articulatory theories hypothesize that listeners would recover articulatory information during the mapping. To test this hypothesis, we altered the acoustic information of the Canadian English sibilants /s/ and /ʃ/ while keeping their articulatory information to signal places of articulation of the original sibilants. The manipulated sibilants were articulatorily cued as the original sibilants, but acoustically cued as the alternative sibilants (/s/ as /ʃ/ and /ʃ/ as /s/). We conducted an identification task to examine whether altering acoustic information would switch our Canadian English listeners’ identification. The listeners identified acoustically /s/-like /ʃ/ completely as the alternative sibilant /s/, but the acoustically /ʃ/-like /s/ as 60% the alternative sibilant /ʃ/ and 40% the original sibilant /s/. There was a categorical switch in the /ʃ/ stimuli but not the /s/ stimuli. This asymmetry of identification between two sibilants can be explained by two accounts: an acoustic plus articulatory account would be that the listeners relied more articulatory information only when identifying /s/ but not /ʃ/; and a purely acoustic account would be that the asymmetry was only a result of still existing small acoustic differences. While the acoustic plus articulatory account cannot explain why articulatory information only influenced the /s/ identification of the /s/ stimuli even after adding a set of assumptions, the purely acoustic account allows us to explain our results consistently without additional assumptions. Although our results cannot be used as evidence to reject the possibility that listeners will recover articulatory information, the results do suggest that even if we assume that articulatory information is recovered, acoustic information is more dominant than articulatory information in the identification process, at least for Canadian English /s/ and /ʃ/. / Thesis / Master of Science (MSc)