Perception of American English Vowels by Spanish-English bilingual listeners

Cross-linguistic studies have demonstrated that learning of a second language (L2) is influenced by the phonological system of the native language (L1), with L2 learners forming mental representations of new, non-native sounds by a process of assimilation to familiar native sounds (Best, 1995; Flege, 1995). Adult sequential successive bilingual Spanish-English speakers may be specifically challenged in perceiving and acquiring American English (AE) vowel contrasts that are signaled by multiple cues not phonemically relevant in their native language. Much of the existing research on vowel perception in L1-Spanish adults has focused on the AE vowel contrast /i/ vs. /ɪ/, as in sheep vs. ship, because discrimination errors between these two vowels are common (Escudero, 2000; Morrison, 2006; 2008; 2009). However, other vowel contrasts /ʌ/-/ɑ/ (as in hut vs. hot) have also been reported to present perceptual challenges for native Spanish-speaking learners of English (Flege, Munro & Mackay, 1995; Escudero & Chládková, 2010). It is assumed that such perceptual issues contribute to poor performance in second language acquisition and processing, and have implications for access to employment and academic opportunities for a large and growing immigrant population in the United States (Labor Employment and Training Administration Report, 2005). The aim of this study is to implement electrophysiological and behavioral methods to further elucidate the perceptual and processing abilities of L1-Spanish adult learners of English, while examining less-studied AE vowel contrasts /ʌ/-/ɑ/, and to evaluate whether specific properties of these speech sounds, such as spectral and duration differences, contribute directly to difficulties encountered in L2 acquisition. More specifically, in this study we will examine response accuracy and reaction time, as well as Mismatch Negativity (MMN) and P300 Event-Related Potentials in two listening conditions: natural vowel duration, where target vowel sounds are presented naturalistically, and neutral vowel duration, in which speech sound discrimination is possible based on spectral cues alone. Event Related Potentials (ERPs - MMN and P300) are neurophysiological indices that can reflect native and non-native mental phonological representations. Findings from the pilot study that utilized natural and neutralized duration speech sounds revealed behavioral and neurophysiological differences between Spanish-English bilingual listeners and native English speakers responses to natural AE vowel contrasts. This raised a question of whether adult Spanish-English bilinguals relied on speech cues in a similar fashion to native English speakers when perceiving these AE vowel contrasts. It is understood that language-specific use of speech cues (e.g. spectral and durational) helps to distinguish between perceptually similar speech sounds. Therefore, it was assumed that removal of duration distinctions between the target vowels would reveal any underlying differences in the processing mechanism and how much L1-Spanish listeners rely on durational cues to perceive subtle differences between vowel pairs. Findings from this dissertation study indicate that adult sequential Spanish-English bilingual listeners (Study group) showed indices of discrimination and identification of AE vowel /ɑ/ but not /ʌ/ at the attentional level, when both spectral and durational information about the vowels was perceptually available in the natural vowel duration condition, but also when duration was neutralized leaving only spectral cues available to distinguish the vowels. The current findings show that Spanish-English bilinguals may use spectral and durational cues, like native English speakers, to perceive the English vowel contrast /ɑ/-/ʌ/. However, this cannot be described as an "end state" in the sense of Escudero (2005), since the neurophysiological evidence shows that these L2 learners are able to reach native-like discrimination only when they recruit attentional and cognitive resources to facilitate the perceptual process