Non-native Vowel Perception Research Articles

Asymmetries in Infants' Vowel Perception: Changes in Vowel Discrimination in German Learning 6- and 9-Month-Old Infants.

Infants' speech perception is characterized by substantial changes during the first year of life that attune the processing mechanisms to the specific properties of the ambient language. This paper focuses on these developmental changes in vowel perception. More specifically, the emergence and potential cause of perceptual asymmetries in vowel perception are investigated by an experimental study on German 6- and 9-month-olds' discrimination of a vowel contrast that is not phonemic in German. Results show discrimination without any asymmetry in the 6-month-olds but an asymmetrical pattern with better performance when the vowel changes from the less focal to the more focal vowel than vice versa by the 9-month-olds. The results concerning the asymmetries are compatible with the Natural Referent Framework as well as with the Native Language Magnet model. Our results foster two main conclusions. First, bi-directional testing must be mandatory when testing vowel perception. Second, when testing non-native vowel perception, the relation of the stimuli to the native language vowel system has to be considered very carefully as this system impacts the perception of non-native vowels.

Language Experience and Subjective Word Familiarity on the Multimodal Perception of Non-native Vowels.

The present study investigated native (L1) and non-native (L2) speakers' perception of the French vowels /ɔ̃, ɑ̃, ɛ̃, o/. Thirty-four American-English learners of French and 33 native speakers of Parisian French were asked to identify 60 monosyllabic words produced by a native speaker in three modalities of presentation: auditory-only (A-only); audiovisual (AV); and visual-only (V-only). The L2 participants also completed a vocabulary knowledge test of the words presented in the perception experiment that aimed to explore whether subjective word familiarity affected speech perception. Results showed that overall performance was better in the AV and A-only conditions for the two groups with the pattern of confusion differing across modalities. The lack of audiovisual benefit was not due to the vowel contrasts being not visually salient enough, as shown by the native group's performance in the V-only modality, but to the L2 group's weaker sensitivity to visual information. Additionally, a significant relationship was found between subjective word familiarity and AV and A-only (but not V-only) perception of non-native contrasts.

Training non-native vowel perception: In quiet or noise.

Noise makes speech perception much more challenging for non-native listeners than for native listeners. Training for non-native speech perception is usually implemented in quiet. It remains unclear if background noise may benefit or hamper non-native speech perception learning. In this study, 51 Chinese-native listeners were randomly assigned into three groups, including vowel training in quiet (TIQ), vowel training in noise (TIN), and watching videos in English as an active control. Vowel identification was assessed before (T1), right after (T2), and three months after training (T3) in quiet and various noise conditions. Results indicated that compared with the video watching group, the TIN group improved vowel identification in both quiet and noise significantly more at T2 and at T3. In contrast, the TIQ group improved significantly more in quiet and also in non-speech noise conditions at T2, but the improvement did not hold at T3. Moreover, compared to the TIQ group, the TIN group showed significantly less informational masking at both T2 and T3 and less energetic masking at T3. These results suggest that L2 speech training in background noise may improve non-native vowel perception more effectively than TIQ background only. The implications for non-native speech perception learning are discussed.

The Role of Acoustic Similarity and Non-Native Categorisation in Predicting Non-Native Discrimination: Brazilian Portuguese Vowels by English vs. Spanish Listeners

This study tests whether Australian English (AusE) and European Spanish (ES) listeners differ in their categorisation and discrimination of Brazilian Portuguese (BP) vowels. In particular, we investigate two theoretically relevant measures of vowel category overlap (acoustic vs. perceptual categorisation) as predictors of non-native discrimination difficulty. We also investigate whether the individual listener’s own native vowel productions predict non-native vowel perception better than group averages. The results showed comparable performance for AusE and ES participants in their perception of the BP vowels. In particular, discrimination patterns were largely dependent on contrast-specific learning scenarios, which were similar across AusE and ES. We also found that acoustic similarity between individuals’ own native productions and the BP stimuli were largely consistent with the participants’ patterns of non-native categorisation. Furthermore, the results indicated that both acoustic and perceptual overlap successfully predict discrimination performance. However, accuracy in discrimination was better explained by perceptual similarity for ES listeners and by acoustic similarity for AusE listeners. Interestingly, we also found that for ES listeners, the group averages explained discrimination accuracy better than predictions based on individual production data, but that the AusE group showed no difference.

Effects of high variability phonetic training on cue reweighting in non-native vowel perception by adult Chinese learners

While native English speakers have been found to primarily use vowel spectrum on /i/-/ɪ/ perception, Chinese learners of English dominantly use vowel duration. This study examined training effects on cue reweighting in perceiving /i/-/ɪ/ by Chinese learners. We modified the canonical HVPT paradigm with introducing variability along the secondary dimension for the contrast distinction (i.e., duration). Forty native Chinese-speaking adults were randomly assigned to two groups: the training group and the control group. Pre- and post- training tests used the tasks of natural word identification and synthetic phoneme identification. Synthesized phoneme stimuli were the two-dimensional (spectrum and duration) stimulus continua ranging from English /i/ to /ɪ/, and the natural word stimuli included both trained and untrained words produced by novel talkers. The results demonstrated that the training group showed more reliance on the primary spectral cue and less reliance on the secondary durational cue after training. The corroborating data from the word identification showed the training group improved significantly and generalized learning to new talkers and phonetic contexts. The control group did not show similar changes. These results indicated that high variability phonetic training is effective on helping L2 learners to retune attention to primary cues which facilitate generalization outcomes.

Acoustic Properties Predict Perception of Unfamiliar Dutch Vowels by Adult Australian English and Peruvian Spanish Listeners.

Research suggests that the size of the second language (L2) vowel inventory relative to the native (L1) inventory may affect the discrimination and acquisition of L2 vowels. Models of non-native and L2 vowel perception stipulate that naïve listeners' non-native and L2 perceptual patterns may be predicted by the relationship in vowel inventory size between the L1 and the L2. Specifically, having a smaller L1 vowel inventory than the L2 impedes L2 vowel perception, while having a larger one often facilitates it. However, the Second Language Linguistic Perception (L2LP) model specifies that it is the L1–L2 acoustic relationships that predict non-native and L2 vowel perception, regardless of L1 vowel inventory. To test the effects of vowel inventory size vs. acoustic properties on non-native vowel perception, we compared XAB discrimination and categorization of five Dutch vowel contrasts between monolinguals whose L1 contains more (Australian English) or fewer (Peruvian Spanish) vowels than Dutch. No effect of language background was found, suggesting that L1 inventory size alone did not account for performance. Instead, participants in both language groups were more accurate in discriminating contrasts that were predicted to be perceptually easy based on L1–L2 acoustic relationships, and were less accurate for contrasts likewise predicted to be difficult. Further, cross-language discriminant analyses predicted listeners' categorization patterns which in turn predicted listeners' discrimination difficulty. Our results show that listeners with larger vowel inventories appear to activate multiple native categories as reflected in lower accuracy scores for some Dutch vowels, while listeners with a smaller vowel inventory seem to have higher accuracy scores for those same vowels. In line with the L2LP model, these findings demonstrate that L1–L2 acoustic relationships better predict non-native and L2 perceptual performance and that inventory size alone is not a good predictor for cross-language perceptual difficulties.

Influences of listeners' native and other dialects on cross-language vowel perception.

This paper examines to what extent acoustic similarity between native and non-native vowels predicts non-native vowel perception and whether this process is influenced by listeners' native and other non-native dialects. Listeners with Northern and Southern British English dialects completed a perceptual assimilation task in which they categorized tokens of 15 Dutch vowels in terms of English vowel categories. While the cross-language acoustic similarity of Dutch vowels to English vowels largely predicted Southern listeners' perceptual assimilation patterns, this was not the case for Northern listeners, whose assimilation patterns resembled those of Southern listeners for all but three Dutch vowels. The cross-language acoustic similarity of Dutch vowels to Northern English vowels was re-examined by incorporating Southern English tokens, which resulted in considerable improvements in the predicting power of cross-language acoustic similarity. This suggests that Northern listeners' assimilation of Dutch vowels to English vowels was influenced by knowledge of both native Northern and non-native Southern English vowel categories. The implications of these findings for theories of non-native speech perception are discussed.

Perceptual Assimilation and Discrimination of Non-Native Vowel Contrasts

Research on language-specific tuning in speech perception has focused mainly on consonants, while that on non-native vowel perception has failed to address whether the same principles apply. Therefore, non-native vowel perception was investigated here in light of relevant theoretical models: the Perceptual Assimilation Model (PAM) and the Natural Referent Vowel (NRV) framework. American-English speakers completed discrimination and native language assimilation (categorization and goodness rating) tests on six nonnative vowel contrasts. Discrimination was consistent with PAM assimilation types, but asymmetries predicted by NRV were only observed for single-category assimilations, suggesting that perceptual assimilation might modulate the effects of vowel peripherality on non-native vowel perception. © 2014 S. Karger AG, Basel

Native Catalan learners' perception and production of English vowels

This paper reports two experiments on nonnative vowel perception and production. In Experiment 1, three groups of Catalan learners varying in English proficiency were tested on their ability to discriminate seven Catalan–English (C–E) and four English–English (E–E) vowel contrasts. The vowel contrasts were natural speech tokens obtained from native Catalan and native American English speakers. On average, listeners distinguished the C–E /i–ɪ/ contrast relatively well, and they could partially distinguish /i–i/, /u–u/, and /a–ɑ/, but they had great difficulty with the /a–ʌ/, /a–æ/ and /ɛ–ɛ/ contrasts. As for the E–E pairs, the learners could discriminate the speech sounds in the /i–ɪ/ and /u–ʊ/ pairs, suggesting that learners may have established new phonetic categories for /ɪ/ and /ʊ/. In Experiment 2, a subgroup of the Catalan learners and a control group of native English speakers produced words containing one of the English vowels /i/, /ɪ/, /ɛ/, /æ/, /ɑ/, /ʌ/, /ʊ/, and /u/. Vowel accuracy was assessed by means of acoustic measurements and by native listener judgments. The acoustic measurements revealed that, in spectral terms, learners produced vowels that were less peripheral than the native English (NE) versions, although there was a tendency for vowel expansion as a function of language proficiency. Vowel duration in the tense–lax vowel pairs also progressed toward more nativelike values in the productions of the more proficient learners. Finally, the NE listener judgments showed that most learners produced the vowels /ɪ/, /æ/, /ʊ/, and /u/ intelligibly but with significantly lower goodness ratings than did the NE speakers.

Neuroanatomical markers of individual differences in native and non-native vowel perception

Abstract Although most human beings experience no difficulty in perceiving their native language, strong individual differences are observed for certain foreign phonemic contrasts. Diaz, Baus, Escera, Costa, and Sebastian-Galles (2008 , Brain potentials to native phoneme discrimination reveal the origin of individual differences in learning the sounds of a second language. Proceedings of the National Academy of Sciences of the United States of America, 105, 16083–16088) reported a correlation between event-related potential (ERP) responses to native and non-native vowels in a group of early and highly-skilled bilinguals. In the present study, we compared the brain morphology of two groups of bilinguals who were equally proficient in their second language but differed in their perception of both native and non-native vowels. A whole brain, voxel-based morphometry analysis (VBM) revealed larger white matter volume in the right insulo/fronto-opercular region in individuals who exhibited poorer perceptual discrimination of native and non-native vowels. As the volume of the left Heschl’s gyri has previously been shown to correlate with the ability to perceive foreign phonemic contrasts (between consonants), we also measured the white and grey matter volumes of Heschl’s gyri in our subjects. We did not observe any significant relation between these volumes and vowel discrimination capabilities. This result allows the identification of anatomical brain differences related to individual differences in vowel perception. The present results add to the relatively unexplored area of the relationship between brain structure and language function in adult healthy population.

Across-talker effects on non-native listeners’ vowel perception in noise

This study explored how across-talker differences influence non-native vowel perception. American English (AE) and Korean listeners were presented with recordings of 10 AE vowels in /bVd/ context. The stimuli were mixed with noise and presented for identification in a 10-alternative forced-choice task. The two listener groups heard recordings of the vowels produced by 10 talkers at three signal-to-noise ratios. Overall the AE listeners identified the vowels 22% more accurately than the Korean listeners. There was a wide range of identification accuracy scores across talkers for both AE and Korean listeners. At each signal-to-noise ratio, the across-talker intelligibility scores were highly correlated for AE and Korean listeners. Acoustic analysis was conducted for 2 vowel pairs that exhibited variable accuracy across talkers for Korean listeners but high identification accuracy for AE listeners. Results demonstrated that Korean listeners' error patterns for these four vowels were strongly influenced by variability in vowel production that was within the normal range for AE talkers. These results suggest that non-native listeners are strongly influenced by across-talker variability perhaps because of the difficulty they have forming native-like vowel categories.

The Effect of L1 Orthography on Non-native Vowel Perception

Previous research has shown that orthography influences the learning and processing of spoken non-native words. In this paper, we examine the effect of L1 orthography on non-native sound perception. In Experiment 1, 204 Spanish learners of Dutch and a control group of 20 native speakers of Dutch were asked to classify Dutch vowel tokens by choosing from auditorily presented options, in one task, and from the orthographic representations of Dutch vowels, in a second task. The results show that vowel categorization varied across tasks: the most difficult vowels in the purely auditory task were the easiest in the orthographic task and, conversely, vowels with a relatively high success rate in the purely auditory task were poorly classified in the orthographic task. The results of Experiment 2 with 22 monolingual Peruvian Spanish listeners replicated the main results of Experiment 1 and confirmed the existence of orthographic effects. Together, the two experiments show that when listening to auditory stimuli only, native speakers of Spanish have great difficulty classifying certain Dutch vowels, regardless of the amount of experience they may have with the Dutch language. Importantly, the pairing of auditory stimuli with orthographic labels can help or hinder Spanish listeners' sound categorization, depending on the specific sound contrast.

Korean listeners’ sensitivity to language-specific phonetic details of children and adults’ vowel production in five different languages.

Systematic differences in vowel production across languages have been demonstrated, even for so-called “shared” vowels. Starting from 10 months of age, language-specific vowel production patterns emerge in babbling [Boysson-Bardies et al. (1989)]. Vowel production data from a word repetition task in our laboratory also showed language-specific patterns emerging at 2 years of age. While there is research on adult and infant perception of non-native vowels produced by adults, there is little work on adult perception of children’s non-native vowels of different languages. The current study examined Korean adult listeners’ perception of vowels from five languages, Cantonese, English, Greek, Japanese, and Korean, produced by 2-, 5-year-old children, and adults. Consonant-vowel and vowel only stimuli were extracted from our vowel production data. Target vowels included /i/, /a/, and /u/, following velar and alveolar stops. Twenty native Korean adult listeners were asked to identify the vowels and rated their goodness. Results will be analyzed using both the formant frequencies and listeners’ judgments using a mixed effect model. [Supported by a Fulbright fellowship, NIDCD Grant 02932, and NSF Grant 0729140.]

Discriminability and identification of English vowels by native Japanese speakers in different consonantal contexts

The purpose of the present experiment was to examine the effects of consonantal context on discrimination and identification of English vowels by native Japanese speakers learning English in Japan. A number of studies have assessed the effects of consonantal contexts on the perception of nonnative vowels. For instance, Strange et al. (1996, 2001) found that perceptual assimilation of nonnative vowels is affected by consonantal contexts, and Morrison (2002) has shown that Japanese speakers use durational cues to perceive English /i/–/I/. The present study revealed that consonantal context affects discriminability and identification of each English vowel differently. Of all the six vowel contrasts tested, /i/–/I/ was the most likely to be affected by voicing status of the surrounding consonants with it being easier to discriminate in voiceless consonantal contexts. Moreover, /I/ is more likely to be equated with the Japanese short vowel /i/ in a voiceless consonantal context which is in keeping with Morrison (2002). /æ/–/ɑ/, on the other hand, is the most strongly affected by the place of articulation of the preceding consonants. [Work supported by Grant-in-Aid for Scientific Research (C)(1)(1410635).]

Cross-language vowel perception and production by Japanese and Korean learners of English

This paper investigates the roles of language-specific phonological learning and inherent phonetic contrastiveness in the perception of non-native vowels. Native speakers of Korean and Japanese, at two levels of English language experience, were assessed on the perception and production of Australian English monophthongal non-back vowels: /i: ı e æ a:/. Prototypicality ratings, or perceived similarities of the foreign vowels to their nearest native (L1) phonemic targets, were also examined, to assess models of cross-language vowel perception. Korean is of interest because of a recent phonological merger of two front vowels (/e/ and /ϵ/), which has produced a generation split among speakers of Seoul dialect above and below 45–50 years of age (Hong, 1991). The present study is the first reported case of how a phonemic merger, resulting in cross-generation differences within a speech community, can influence speakers' perception and production of non-native vowels. The effects of L1 phonological learning on vowel perception were also observed in the tendency of the Japanese, but not the Korean listeners, to normalize tokens of non-native vowels for speaker-dependent durational variation, consistent with the respective phonological roles of vowel length in Japanese and Korean.

A developmental study of native and non-native vowel perception

Two vowel continua were created using the Klatt synthesizer. F1 frequency varied in the same eight equal mel steps in both. F2 frequency also varied in eight equal mel steps but, whereas it increased relative to /i/ in one continuum, it decreased relative to /i/ in the other. As a result, vowels in the ‘‘native–native’’ continuum ranged from /i/ to /i/, those in the native-foreign continuum from /i/ to a vowel symbolized as /Y/. Adults and children ranging in age from 4 to 12 years (ten per group) were trained to identify the endpoints of both continua as either /i/ or ‘‘the other vowel.’’ There was no effect of subjects’ age on the number of stimuli identified as /i/. This failed to support the hypothesis that vowels not bounded by another native language category−such as /i/ in the /i/–/Y/ but not the /i/–/i/ continuum−will expand outward with age. Slope analyses revealed that the 4- to 6-year-old children had shallower identification functions than the adults. Much the same effect of age was evident for the /i/–/i/ and /i/–/Y/ continua. This argues against attributing the observed age effect on slopes to a poorer definition of vowel categories by the 4- to 6-year-olds than by the adults. In metalinguistic tests, the 4-year-olds performed a rhyming task more poorly than 5- to 8-year-olds. The 4- and 5-year-olds were less able than 6- to 8-year-olds to segment initial and final consonants. The slope differences may therefore have arisen from age-related differences in ability to perform perceptual tasks involving localized sound segments. [Work supported by NIH.]