Vowel Categories Research Articles

Vowel qualities in monosyllabic words in Namibian English

This study investigated how Namibian English speakers produce vowel qualities in controlled speech. Participants were 14 proficient Namibian English speakers, who produced monosyllabic English CVC words, presented in orthographic form. The first and second formant values were extracted from the speakers’ productions to determine the vowel qualities in each word. The formant values produced by the Namibian English speakers were then compared to those produced by nine British English speakers, obtained from a previous study, in order to examine how Namibian English vowel qualities relate to British English vowel categories. The results showed a great deal of variation and overlap in the Namibian vowel categories, particularly in the close front vowels and open and close back vowels. This resulted in the formation of five to six clusters of vowel qualities. This is likely an effect of the varied linguistic backgrounds of the participants. Furthermore, the Namibian English vowels differed significantly from most British English vowels, especially in the F2 formant. Some commonalities with earlier research into Namibian English vowel qualities was found in the fronting, backing and mergers of some vowel categories.

The acoustic characteristics of Swedish vowels.

The Swedish vowel space is relatively densely populated with 21 categories that differ in quality and quantity. Existing descriptions of the entire space rest on recordings made in the late 1990s or earlier, while recent work in general has focused on subsets of the space. The present paper reports on static and dynamic acoustic analyses of the entire vowel space using a recently released database of h-VOWEL-d words (SwehVd). The results highlight the importance of static and dynamic spectral and temporal cues for Swedish vowel category distinction. The first two formants and vowel duration are the primary acoustic cues to vowel identity, however, the third formant contributes to increased category separability for neighboring contrasts presumed to differ in lip-rounding. In addition, even though all long-short vowel pairs differ systematically in duration, they also display considerable spectral differences, suggesting that quantity distinctions are not separate from quality distinctions in Swedish. The dynamic analysis further suggests formant movements in both long and short vowels, with [e:] and [o:] displaying clearer patterns of diphthongization.

The Stability of the trap-bath Split in the East Midlands

This article reviews the status of the trap-bath split in the counties of Leicestershire, Nottinghamshire, and Derbyshire in the East Midlands of England. The East Midlands forms a linguistic transition zone between northern English varieties which lack (part of) the trap-bath split, and southern English varieties which have this split. We examine the acoustic properties of trap and bath in the region to determine whether this pattern is stable over time or diffusing. Reading-passage data, stratified by age group, sex, and location are used to provide an apparent time and multilocal view on the distribution of the two vowel categories. Results suggest there is no complete overlap between these vowel sets in the region, although it varies across the East Midlands. Furthermore, we find the East Midlands apparently occupies a stable middle ground between northern and south-eastern varieties.

Dynamic acoustic vowel distances within and across dialects.

Vowels vary in their acoustic similarity across regional dialects of American English, such that some vowels are more similar to one another in some dialects than others. Acoustic vowel distance measures typically evaluate vowel similarity at a discrete time point, resulting in distance estimates that may not fully capture vowel similarity in formant trajectory dynamics. In the current study, language and accent distance measures, which evaluate acoustic distances between talkers over time, were applied to the evaluation of vowel category similarity within talkers. These vowel category distances were then compared across dialects, and their utility in capturing predicted patterns of regional dialect variation in American English was examined. Dynamic time warping of mel-frequency cepstral coefficients was used to assess acoustic distance across the frequency spectrum and captured predicted Southern American English vowel similarity. Root-mean-square distance and generalized additive mixed models were used to assess acoustic distance for selected formant trajectories and captured predicted Southern, New England, and Northern American English vowel similarity. Generalized additive mixed models captured the most predicted variation, but, unlike the other measures, do not return a single acoustic distance value. All three measures are potentially useful for understanding variation in vowel category similarity across dialects.

Factors influencing vowel adaptation in English loanwords in Korean

Abstract This study explores the extent to which perceptual and other factors (i.e., orthography and standardization) affect vowel adaptation in English loanwords in Korean. It also examines whether perceptual variability gives rise to adaptation variability, and it further addresses whether the degree of perceptual influence in vowel adaptation is different from that in consonant adaptation. Data on Korean listeners’ perceptual mapping patterns for English vowels were collected in an English-to-Korean vowel category mapping experiment and compared to the patterns in a loanword database. The results indicate that perceptual factors have a great impact on the adaptation of English vowels into Korean, in line with de Jong and Cho’s (de Jong, Kenneth & Mi-Hui Cho. 2012. Loanword phonology and perceptual mapping: Comparing two corpora of Korean contact with English. Language 88. 341–368) findings for the adaptation of English consonants into Korean. Consequently, factors such as orthography and standardization are viewed as deviations from these perceptual influences. The impact of perceptual adaptation is, however, rather limited because the correlation between perceptual mappings and loanword mappings is less robust for English vowel adaptation than for English consonant adaptation possibly due to the less categorical nature of vowels relative to consonants. Additionally, the results show that increased strength of modal perceptual mappings is related to less loanword variability in vowel adaptation.

More foreign-accented but more comprehensible: Attrition and amelioration of L1 speech in proficient L2 learners.

There is an increasing interest in cross-linguistic influences of the second language (L2) on the first (L1), but its communicative impact remains to be elucidated. This study investigates how L2 learners' L1 pronunciation is perceived as foreign-accented and (in) comprehensible as a function of their L2 learning experience and proficiency levels. Read speech of 154 L1 Japanese learners of L2 English in the J-AESOP corpus was examined, where approximately one-third of them had lived in English-speaking countries and the rest had never lived outside of Japan. Their L1 speech was rated by another group of native Japanese listeners for accentedness and comprehensibility (from October 25, 2022 to August 20, 2023), while their L2 speech was previously rated by native American English listeners for nativelikeness or proficiency. The speakers' vowel acoustics were also examined. More proficient L2 speakers were perceived as more foreign-accented in their L1, but only if they had lived overseas; their length of residence abroad predicted the degree of perceived accentedness. In contrast, more proficient L2 speakers were consistently perceived as more comprehensible in the L1, regardless of prior overseas experience. Acoustic analyses indicated that perceived accentedness is associated with a clockwise chain shift of all vowel categories in the vowel space. It was also revealed that the dispersion, rather than compactness, of vowel production contributed to perceived comprehensibility, although the degree of L1 vowel dispersion did not predict L2 proficiency. The overall results suggest two main conclusions. First, perceptible L1 foreign accent likely results from L1 disuse rather than L2 interference, thereby L1 pronunciation differs from native norms at a system-wide rather than category-specific level. Second, L2 learning has a positive influence on perceived L1 comprehensibility, rather than individuals with clearer and more comprehensible L1 speech being inherently better L2 learners.

The Articulatory and Acoustic Representation of Second-Language French Vowels.

This study examines how L1 English-L2 French learners use L1 articulatory and acoustic categories to produce L2 vowels that are both similar to and different from their L1 vowels. Previous studies examining the relationship between L1 and L2 sound inventories have found that learners reuse L1 phone categories to produce L2 phones that are perceived as similar, but importantly, there is a lack of articulatory data included in these types of studies, which has reinforced the assumption that vowel categories can be solely represented by their acoustic properties. The present study uses ultrasound tongue imaging data and videos of lip rounding in addition to acoustic data to examine how L1 English-L2 French learners produce the French vowels /i y u e ø o/ compared with their English vowels /i u e o/. The results focus on individual paths to category formation to show how learners articulate L2 vowels, and reveal that they tend to reuse L1 tongue body gestures to produce the French vowels /i u e o/, and lip rounding gestures to produce the round vowels /y u o/. This study demonstrates that transfer of articulatory gestures depends on vowel quality and emphasizes the importance of using articulatory data to inform theories of L2 category formation.

Crossmodal correspondence between lexical tones and visual motions: a forced-choice mapping task on Mandarin Chinese

Abstract Crossmodal correspondence refers to the phenomenon in which individuals match stimulus features (e.g., auditory pitch) with different sensory modalities (e.g., visual size). While studies on correspondences exhibited by suprasegmentals have mostly focused on pitch-size and pitch-shape associations, audiospatial binding observed in the production and perception of Mandarin tones, where pitch of the syllable distinguishes word meanings, sheds light on the symbolic potential of auditory pitch. In the present study, a forced-choice mapping task was conducted in the form of a word guessing game, where native Mandarin listeners select the meaning of an auditory “alien” word from two visual motions. The results showed that: (1) listeners reliably match auditory tones with visual motions in the way that pitch trajectories are congruent with spatial movements, (2) vowel category impacts tone-motion correspondence when syllables are articulated in non-contour tones, and (3) the capacities in driving the tone-motion correspondence are different across tonal categories. These findings further contribute to our understanding of the sound symbolic potential of lexical tones and expand the boundary of crossmodal correspondence that can be demonstrated by pitch.

Compactness of Native Vowel Categories in Monolingual, Bilingual, and Multilingual Speakers: Is Category Compactness Affected by the Number of Languages Spoken?

Phonetic category compactness pertains to the degree of variation or dispersion within a specific category. Previous research has shown that more compact native (L1) categories in production have been related to the discrimination of non-native sounds in perception and production. The understanding of the factors influencing L1 category compactness remains limited. Some proposals suggest that compactness may be influenced by individual differences in cognitive processes. Alternatively, category compactness could be linked to linguistic factors, such as the number of languages spoken or the density of the phonological system. This study investigates the latter hypothesis. This study examined category compactness in perception for three L1 Spanish vowels /i/, /e/, and /a/ across four participant groups: 12 monolinguals, 31 functional monolinguals, 24 bilinguals, and 19 multilinguals. To measure compactness in perception, the study employed a perceptual categorization task consisting of synthesized variants of /i/, /e/, and /a/. Participants were asked to label these variants as either acceptable or unacceptable members of their L1 /i/, /e/, and /a/ categories. The findings revealed significant differences in category compactness between monolingual and bi/multilingual speakers. More specifically, bilingual and multilingual speakers had larger/less compact L1 vowel categories than monolinguals. The substantial variability in compactness across all groups suggests that compactness may be influenced by a range of other individual differences, besides the number of languages spoken.

Acoustic Analyses of L1 and L2 Vowel Interactions in Mandarin–Cantonese Late Bilinguals

While the focus of bilingual research is frequently on simultaneous or early bilingualism, the interactions between late bilinguals’ first language (L1) and second language (L2) have rarely been studied previously. To fill this research gap, the aim of the current study was to investigate the production of vowels in the L1 Mandarin and L2 Cantonese of Mandarin–Cantonese late bilinguals in Hong Kong. A production experiment was conducted with 22 Mandarin–Cantonese bilinguals, as well as with 20 native Mandarin speakers and 21 native Cantonese speakers. Acoustic analyses, including formants of and Euclidean distances between the vowels, were performed. Both vowel category assimilation and dissimilation were noted in the Mandarin–Cantonese bilinguals’ L1 and L2 vowel systems, suggesting interactions between the bilinguals’ L1 and L2 vowel categories. In general, the findings are in line with the hypotheses of the Speech Learning Model and its revised version, which state that L1–L2 phonetic interactions are inevitable, as there is a common phonetic space for storing the L1 and L2 phonetic categories, and that learners always have the ability to adapt their phonetic space. Future studies should refine the data elicitation method, increase the sample size and include more language pairs to better understand L1 and L2 phonetic interactions.

The effect of musical expertise on whistled vowel identification

In this paper, we looked at the impact of musical experience on whistled vowel categorization by native French speakers. Whistled speech, a natural, yet modified speech type, augments speech amplitude while transposing the signal to a range of fairly high frequencies, i.e. 1 to 4 kHz. The whistled vowels are simple pitches of different heights depending on the vowel position, and generally represent the most stable part of the signal, just as in modal speech. They are modulated by consonant coarticulation(s), resulting in characteristic pitch movements. This change in speech mode can liken the speech signal to musical notes and their modulations; however, the mechanisms used to categorize whistled phonemes rely on abstract phonological knowledge and representation. Here we explore the impact of musical expertise on such a process by focusing on four whistled vowels (/i, e, a, o/) which have been used in previous experiments with non-musicians. We also included inter-speaker production variations, adding variability to the vowel pitches. Our results showed that all participants categorize whistled vowels well over chance, with musicians showing advantages for the middle whistled vowels (/a/ and /e/) as well as for the lower whistled vowel /o/. The whistler variability also affects musicians more than non-musicians and impacts their advantage, notably for the vowels /e/ and /o/. However, we find no specific training advantage for musicians over the whole experiment, but rather training effects for /a/ and /e/ when taking into account all participants. This suggests that though musical experience may help structure the vowel hierarchy when the whistler has a larger range, this advantage cannot be generalized when listening to another whistler. Thus, the transfer of musical knowledge present in this task only influences certain aspects of speech perception.

Quantifying vowel category distinctness using Bayesian modelling

Phonetic and sociolinguistic studies of vowel merger require a measure of acoustic distinctness between vowel categories. Three desiderata for such a metric are that it be multivariate, in the sense that it account for correlations between dimensions (e.g., F1 and F2), control for other factors affecting vowel formants (e.g. surrounding consonants), and work for unbalanced data (common in naturalistic data). Previous work (Nycz and Hall-Lew, 2013; Kelley & Tucker, 2020) has considered a variety of measures, including variants of Euclidean distance, Pillai score, and Bhattacharyya affinity, but none meet all three criteria. We present a new method for quantifying vowel merger that meets all desiderata and can be applied to different metrics: we fit a Bayesian mixed-effects linear model to jointly predict F1 and F2, then compute any desired metric—here, Euclidean distance, Pillai score, and Bhattacharyya affinity—from the posterior. We evaluate each metric, and the overall method, to describe PIN-PEN across a range of English dialect corpora. We find that controlling for covariates and unbalanced data adds substantial signal, but that multivariate modelling does not perform substantially better than univariate modelling. Additionally, we argue that Bhattacharyya affinity has particularly desirable properties (e.g., allowing for heteroskedastic data: Johnson, 2015).

Acoustic vowel distances within and across dialects

Regional dialects of American English exhibit variation in the phonetic realization of vowel categories. This variation leads to different degrees of phonetic vowel similarity within and across dialects. This vowel similarity has been captured by measures of formant distance and overlap in the acoustic space, typically with static formant estimates from a single timepoint in the vowel. In contrast, dialect similarity has been assessed using measures of acoustic distance over time. In the current study, dynamic measures of acoustic distance, including dynamic time warping, root mean-square distance, and generalized additive mixed effect models, were used to assess within-dialect vowel category distances and to compare these distances across dialects. The results were generally consistent across the different distance metrics, confirming their respective ability to capture acoustic vowel distance. However, the magnitude of the distances varied across dialects and vowel variables. Whereas some dialect-specific variables showed the expected patterns of within- and across-dialect similarity based on previous descriptive work, other variables did not. These mixed findings have implications for our understanding of regional dialect variation in American English, its effect on acoustic vowel similarity, and the relationship between acoustic vowel similarity and perceptual ambiguity of vowel contrasts within and across dialects.

Neurophysiological correlates of the perceptual magnet effect in speech perception

This study investigated the Perceptual Magnet Effect (PME) in speech perception using behavioral and Event-Related Potentials (ERP) measures. There were two primary research questions: (1) whether category goodness rating influences speech discrimination with reduced sensitivity near the prototype and increased sensitivity in the vicinity of a poor exemplar, (2) whether the PME is domain-specific to speech sounds. Twenty adult native English speakers participated in identification, goodness rating, and discrimination tasks. The stimuli were synthesized vowels for /a/ and their nonspeech analogs by systematically varying the first two formants. ERP oddball conditions included four conditions presented in a counter-balanced order with the prototypical /a/ as the standard stimuli and its variants as deviants, and a non-prototypical /a/ as the standard and its variants as deviants, as well as the nonspeech matches. Results indicated that participants rated vowel category goodness based on the F2/F1 ratio for the /a/ sounds. Mismatch negativity amplitudes in the two speech conditions aligned with PME predictions, but similar patterns were also observed in the nonspeech conditions. The findings collectively demonstrated neurophysiological evidence for the perceptual organization of within-category variations in line with PME, which may transfer to auditory processing of similar acoustic patterns in nonspeech.

Unexpected findings from L2 speech research can help us understand how humans process vowels

Research on nonnative speakers’ vowel production and perception has provided us with a number of surprising insights on how learners cope with nonnative vowels. Three of these initially unexpected, yet later solidly replicated, findings will be presented: (1) A decline in intelligibility of nonnative vowels as general proficiency improves (when an increase in intelligibility will be expected), (2) the use of acoustic cues in L2 vowel perception that cannot be attributed to transfer from the native language, and that are nonfunctional in the L2, and (3) the maintenance from infant speech perception in adult cross-language vowel perception of a bias favoring peripheral vowels. This presentation will discuss implications of these findings for our understanding of how vowel categories coexist in the minds of multilinguals, and of universally (native-language independent) preferred ways of vowel perception.

Influence of the European Portuguese phonological system on the perception of close-mid and open-mid vowels

This study’s purpose was to analyse the influence of neutralisation on the perception of European Portuguese (EP) close-mid and open-mid vowels, and the gradient between the /i/, /e/, /ε/ and /a/ phonological categories. A fuzzy boundary between mid-vowels has been described in the phonological systems of various languages including EP, a variety of Portuguese with complex phonological phenomena and exceptional realisations of vowels in different contexts. Fifteen listeners from Lisbon participated in two tasks: Identification and goodness rating of 20 random repetitions of 31 stimuli from a /i/-/e/-/ε/-/a/ continuum. The boundaries between categories in the identification task, the internal structures of each category and the gradient of each boundary in the goodness rating task were analysed. Logistic regression was used to analyse the individual responses of listeners and the internal structure of phonemic categories, and prototypes were determined using bubble charts of goodness scores. The gradient of boundaries was analysed using two sets of data: X responses and goodness ratings. Models of the gradients of transition were developed using a mixed effects regression approach. Results from the identification task showed four vowel categories marked by three distinct boundaries. The stimulus with the highest score was approximately in the centroid and the goodness score decreased as the stimulus moved away from the centroid, which constitutes new evidence of an internal structure of the phonemic categories in EP. The main implications of the results obtained are for the description and typology of phonological phenomena in EP, supporting the existence of a non-partial contrast (which does not neutralise in any context) between /ε/ and /a/, and revealing less robust /i/-/e/ and /e/-/ε/ phonemic oppositions.

Sentences used in the speech-to-song illusion: Comparisons of acoustic vowel space

In the speech-to-song illusion, certain spoken sentences start sounding like song when repeated several times. This perceptual transformation does not occur for all stimuli, suggesting that acoustic properties of the stimulus may contribute to the illusion. We investigated the contribution of the acoustic properties of vowels to this phenomenon by analyzing the acoustic vowel-space area bounded by formant frequencies of /i/, /æ/, and / ɔ/ in a dataset of transforming ( illusion) and non-transforming ( non-illusion) stimuli. In general, larger vowel-space areas are associated with more acoustic distinctions between vowel categories. We found that the overall vowel space was larger in non-illusion than illusion stimuli. A possible reason for this difference may be that listeners learn to associate large vowel spaces with speech and small vowel spaces with song through exposure to differences between formant frequencies in spoken and sung vowels. We propose that the shifted vowel spaces in which non-illusion sentences may be associated with speech perception thereby activate speech processing circuitry that inhibits the illusion of their transformation into song.

An auditory perspective on phonological development in infancy.

The auditory system encodes the phonetic features of languages by processing spectro-temporal modulations in speech, which can be described at two time scales: relatively slow amplitude variations over time (AM, further distinguished into the slowest <8-16 Hz and faster components 16-500 Hz), and frequency modulations (FM, oscillating at higher rates about 600-10 kHz). While adults require only the slowest AM cues to identify and discriminate speech sounds, infants have been shown to also require faster AM cues (>8-16 Hz) for similar tasks. Using an observer-based psychophysical method, this study measured the ability of typical-hearing 6-month-olds, 10-month-olds, and adults to detect a change in the vowel or consonant features of consonant-vowel syllables when temporal modulations are selectively degraded. Two acoustically degraded conditions were designed, replacing FM cues with pure tones in 32 frequency bands, and then extracting AM cues in each frequency band with two different low-pass cut- off frequencies: (1) half the bandwidth (Fast AM condition), (2) <8 Hz (Slow AM condition). In the Fast AM condition, results show that with reduced FM cues, 85% of 6-month-olds, 72.5% of 10-month-olds, and 100% of adults successfully categorize phonemes. Among participants who passed the Fast AM condition, 67% of 6-month-olds, 75% of 10-month-olds, and 95% of adults passed the Slow AM condition. Furthermore, across the three age groups, the proportion of participants able to detect phonetic category change did not differ between the vowel and consonant conditions. However, age-related differences were observed for vowel categorization: while the 6- and 10-month-old groups did not differ from one another, they both independently differed from adults. Moreover, for consonant categorization, 10-month-olds were more impacted by acoustic temporal degradation compared to 6-month-olds, and showed a greater decline in detection success rates between the Fast AM and Slow AM conditions. The degradation of FM and faster AM cues (>8 Hz) appears to strongly affect consonant processing at 10 months of age. These findings suggest that between 6 and 10 months, infants show different developmental trajectories in the perceptual weight of speech temporal acoustic cues for vowel and consonant processing, possibly linked to phonological attunement.

Phonetic accommodation in non-native directed speech supports L2 word learning and pronunciation

This study assessed whether Non-native Directed Speech (NNDS) facilitates second language (L2) learning, specifically L2 word learning and production. Spanish participants (N = 50) learned novel English words, presented either in NNDS or Native-Directed Speech (NDS), in two tasks: Recognition and Production. Recognition involved matching novel objects to their labels produced in NNDS or NDS. Production required participants to pronounce these objects’ labels. The novel words contained English vowel contrasts, which approximated Spanish vowel categories more (/i-ɪ/) or less (/ʌ-æ/). Participants in the NNDS group exhibited faster recognition of novel words, improved learning, and produced the /i-ɪ/ contrast with greater distinctiveness in comparison to the NDS group. Participants’ ability to discriminate the target vowel contrasts was also assessed before and after the tasks, with no improvement detected in the two groups. These findings support the didactic assumption of NNDS, indicating the relevance of the phonetic adaptations in this register for successful L2 acquisition.

Listener beliefs and perceptual learning: Differences between device and human guises

Abstract: Listeners have a remarkable ability to adapt to novel speech patterns, such as a new accent or an idiosyncratic pronunciation. In almost all of the previous studies examining this phenomenon, the participating listeners had reason to believe that the speech signal was produced by a human being. However, people are increasingly interacting with voice-activated artificially intelligent (voice-AI) devices that produce speech using text-to-speech (TTS) synthesis. Will listeners also adapt to novel speech input when they believe it is produced by a device? Across three experiments, we investigate this question by exposing American English listeners to shifted pronunciations accompanied by either a ‘human’ or a ‘device’ guise and testing how this exposure affects their subsequent categorization of vowels. Our results show that listeners exhibit perceptual learning even when they believe the speaker is a device. Furthermore, listeners generalize these adjustments to new talkers, and do so particularly strongly when they believe that both old and new talkers are devices. These results have implications for models of speech perception, theories of human-computer interaction, and the interface between social cognition and linguistic theory.