More than just methods: Data and insights guide vowel acoustics research.

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

Phonetic convergence to Southern American English: Acoustics and perception.

Phonetic convergence is linguistically and socially selective. The current study examined the constraints on this selectivity in convergence to Southern American English by non-Southern Americans in a word shadowing task. Participants were asked either to repeat the words after the model talker, to repeat the words after the model talker from Louisville, KY, or to imitate the way the model talker from Louisville, KY, said the words, in a between-subject design. Acoustic analysis of the participants' productions revealed significant phonetic convergence on word duration and back vowel fronting, but not on /aɪ/ monophthongization, across all three instruction conditions. These findings suggest social selectivity such that convergence on stereotyped variants is avoided, but convergence to a talker with a non-prestigious variety is not. A perceptual assessment of convergence confirmed the acoustic results, but also revealed significantly more convergence in the explicit imitation condition than in the two repetition conditions. These findings suggest that explicit instructions to imitate lead to greater convergence overall, but do not completely override social selectivity. A comparison of the acoustic and perceptual assessments of convergence indicates that they provide complementary insights into specific features and holistic patterns of convergence, respectively.

Acoustic cues and linguistic experience as factors in regional dialect classification.

Listeners are able to classify talkers by regional dialect of their native language when provided with even short speech samples. However, the way in which American English listeners use segmental and prosodic information to make such decisions is largely unknown. This study used a free classification task to assess native American English listeners' ability to group together talkers from six major dialect regions of American English. Listeners residing in Ohio and Texas were provided with a sentence-long (experiment 1) or paragraph-long (experiment 2) speech sample produced by talkers from each of the six regions presented in one of three conditions: unmodified, monotonized (i.e., flattened F0), and low-pass filtered (i.e., spectral information above 400 Hz removed). In both experiments, listeners in the unmodified and monotonized conditions made more accurate groupings, reflecting their reliance on segmental properties for classifying regional variation. Accuracy was highest for Northern and Western talkers (experiment 1) and Mid-Atlantic talkers (experiment 2). Listeners with experience with multiple dialects as a result of geographic mobility did not show increased accuracy, suggesting a complex relationship between linguistic experience and the perception of available acoustic cues to socioindexical variation.

The Development of Regional Dialect Locality Judgments and Language Attitudes Across the Life Span.

The development of language attitudes and perception of talker regional background was investigated across the life span (N = 240, age range = 4-75 years). Participants rated 12 talkers on dimensions of geographic locality, status, and solidarity. Children could classify some dialects by locality by age 6-7 years and showed adult-like patterns by age 8 years. Children showed adult-like status ratings for some dialects by age 4-5 years but were not fully adult-like until age 12 years. Solidarity ratings were more variable and did not exhibit a clear developmental trajectory, although some adult-like patterns were in place by age 6-7 years. Locality ratings were a significant but modest predictor of attitude ratings, suggesting that geographic knowledge is one contributor to language attitudes throughout development.

Variation in /u/ fronting in the American Midwest.

Previous research has suggested that a greater degree of social indexing of gender, race, and regional background is produced in linguistic contexts that promote phonetic reduction. The goal of the current study was to explore this hypothesis through an examination of the realization of an ongoing sound change in the American Midwest-/u/ fronting-as a function of four linguistic factors that contribute to phonetic reduction: lexical frequency, phonological neighborhood density, discourse mention, and speaking style. The results revealed minimal effects of the linguistic factors on the degree of /u/ fronting among talkers with greater overall advancement in the /u/ fronting change-in-progress, suggesting that the process of /u/ fronting is nearing completion among some American Midwesterners. However, the results also revealed more /u/ fronting in plain laboratory speech than in clear laboratory speech and in low-frequency, low-density words than in low-frequency, high-density words among talkers with lower overall advancement in the /u/ fronting change-in-progress. The directions of these effects are consistent with the hypothesis that social indexing is greater in reduction-promoting contexts. Further, the relative sizes of these effects suggest that speaking style contributes more to variability in social indexing than lexical properties, such as frequency and neighborhood density.

Subphonemic Variation and Lexical Processing: Social and Stylistic Factors.

Different pronunciation variants of the same word can facilitate lexical access, but they may be more or less effective primes depending on their phonological form, stylistic appropriateness, familiarity, and social prestige, suggesting that multiple phonological variants are encoded in the lexicon with varying strength. The current study investigated how subphonemic variation is encoded using a lexical decision task with cross-modal form priming. The results revealed that the magnitude of priming was mediated by stylistic and social properties of the auditory primes, including speaking style, talker dialect, and duration. These interactions provide evidence that phonetically reduced forms and forms that are not socially prestigious are not as robustly encoded in the lexicon as canonical forms and forms produced in prestigious varieties.

Introduction to the Special Issue on Advancing Methods for Analyzing Dialect Variation.

Documenting and analyzing dialect variation is traditionally the domain of dialectology and sociolinguistics. However, modern approaches to acoustic analysis of dialect variation have their roots in Peterson and Barney's [(1952). J. Acoust. Soc. Am. 24, 175-184] foundational work on the acoustic analysis of vowels that was published in the Journal of the Acoustical Society of America (JASA) over 6 decades ago. Although Peterson and Barney (1952) were not primarily concerned with dialect variation, their methods laid the groundwork for the acoustic methods that are still used by scholars today to analyze vowel variation within and across languages. In more recent decades, a number of methodological advances in the study of vowel variation have been published in JASA, including work on acoustic vowel overlap and vowel normalization. The goal of this special issue was to honor that tradition by bringing together a set of papers describing the application of emerging acoustic, articulatory, and computational methods to the analysis of dialect variation in vowels and beyond.

Effects of Lexical Competition and Dialect Exposure on Phonological Priming.

A cross-modal lexical decision task was used to explore the effects of lexical competition and dialect exposure on phonological form priming. Relative to unrelated auditory primes, matching real word primes facilitated lexical decision for visual real word targets, whereas competing minimal pair primes inhibited lexical decision. These effects were robust across two English vowel pairs (mid-front and low-front) and for two listener groups (mono-dialectal and multi-dialectal). However, both the most robust facilitation and the most robust inhibition were observed for the mid-front vowel words with few phonological competitors for the mono-dialectal listener group. The mid-front vowel targets were acoustically more distinct than the low-front vowel targets, suggesting that acoustic-phonetic similarity leads to stronger lexical competition and less robust facilitation and inhibition. The multi-dialectal listeners had more prior exposure to multiple different dialects than the mono-dialectal group, suggesting that long-term exposure to linguistic variability contributes to a more flexible processing strategy in which lexical competition extends over a longer period of time, leading to less robust facilitation and inhibition.

Effects of local lexical competition and regional dialect on vowel production.

Global measures of lexical competition, such as lexical neighborhood density, assume that all phonological contrasts contribute equally to competition. However, effects of local phonetic similarity have also been observed in speech production processes, suggesting that some contrasts may lead to greater competition than others. In the current study, the effect of local lexical competition on vowel production was examined across two dialects of American English that differ in the phonetic similarity of the low-front and low-back vowel pairs. Results revealed a significant interaction between regional dialect and local lexical competition on the acoustic distance within each vowel pair. Local lexical contrast led to greater acoustic distance between vowels, as expected, but this effect was significantly enhanced for acoustically similar dialect-specific variants. These results were independent of global neighborhood density, suggesting that local lexical competition may contribute to the realization of sociolinguistic variation and phonological change.

Children's perception of dialect variation.

A speaker's regional dialect is a rich source of information about that person. Two studies examined five- to six-year-old children's perception of regional dialect: Can they perceive differences among dialects? Have they made meaningful social connections to specific dialects? Experiment 1 asked children to categorize speakers into groups based on their accent; Experiment 2 asked them to match speakers to (un)familiar cultural items. Each child was tested with two of the following: the child's Home dialect, a Regional variant of that dialect, and a Second-Language variant. Results showed that children could successfully categorize only with a Home vs. Second-Language dialect contrast, but could reliably link cultural items with either a Home vs. Second-Language or a Regional vs. Second-Language dialect contrast. These results demonstrate five- to six-year-old children's developing perceptual skill with dialect, and suggest that they have a gradient representation of dialect variation.

Relative Contributions of Social, Contextual, and Lexical Factors in Speech Processing.

This exploratory study examined the simultaneous interactions and relative contributions of bottom-up social information (regional dialect, speaking style), top-down contextual information (semantic predictability), and the internal dynamics of the lexicon (neighborhood density, lexical frequency) to lexical access and word recognition. Cross-modal matching and intelligibility in noise tasks were conducted with a community sample of adults at a local science museum. Each task featured one condition in which keywords were presented in isolation and one condition in which they were presented within a multiword phrase. Lexical processing was slower and more accurate when keywords were presented in their phrasal context, and was both faster and more accurate for auditory stimuli produced in the local Midland dialect. In both tasks, interactions were observed among stimulus dialect, speaking style, semantic predictability, phonological neighborhood density, and lexical frequency. These interactions revealed that bottom-up social information and top-down contextual information contribute more to speech processing than the internal dynamics of the lexicon. Moreover, the relatively stronger bottom-up social effects were observed in both the isolated word and multiword phrase conditions, suggesting that social variation is central to speech processing, even in non-interactive laboratory tasks. At the same time, the specific interactions observed differed between the two experiments, reflecting task-specific demands related to processing time constraints and signal degradation.

Regional dialect perception across the lifespan: Identification and discrimination.

Although adult listeners can often identify a talker's region of origin based on his or her speech, young children typically fail in dialect perception tasks, and little is known about the development of regional dialect representations from childhood into adulthood. This study explored listeners' understanding of the indexical importance of American English regional dialects across the lifespan. Listeners between 4 and 79 years old in the Midwestern United States heard talkers from the Midland, Northern, Southern, and New England regions in two regional dialect perception tasks: identification and discrimination. The results showed that listeners as young as 4-5 years old understand the identity-marking significance of some regional dialects, although adult-like performance was not achieved until adolescence. Further, the findings suggest that regional dialect perception is simultaneously impacted by the specific dialects involved and the cognitive difficulty of the task.

Effects of semantic predictability and regional dialect on vowel space reduction.

This study explored the interaction between semantic predictability and regional dialect variation in an analysis of speech produced by college-aged female talkers from the Northern, Midland, and Southern dialects of American English. Previous research on the effects of semantic predictability has shown that vowels in high semantic predictability contexts are temporally and spectrally reduced compared to vowels in low semantic predictability contexts. In the current study, an analysis of vowel duration confirmed temporal reduction in the high predictability condition. An analysis of vowel formant structure and vowel space dispersion revealed overall spectral reduction for the Southern talkers. For the Northern talkers, more extreme Northern Cities shifting occurred in the high predictability condition than in the low predictability condition. No effects of semantic predictability were observed for the Midland talkers. These findings suggest an interaction between semantic and indexical factors in vowel reduction processes.

Perception of dialect variation in noise: intelligibility and classification.

Listeners can explicitly categorize unfamiliar talkers by regional dialect with above-chance performance under ideal listening conditions. However, the extent to which this important source of variation affects speech processing is largely unknown. In a series of four experiments, we examined the effects of dialect variation on speech intelligibility in noise and the effects of noise on perceptual dialect classification. Results revealed that, on the one hand, dialect-specific differences in speech intelligibility were more pronounced at harder signal-to-noise ratios, but were attenuated under more favorable listening conditions. Listener dialect did not interact with talker dialect; for all listeners, at a range of noise levels, the General American talkers were the most intelligible and the Mid-Atlantic talkers were the least intelligible. Dialect classification performance, on the other hand, was poor even with only moderate amounts of noise. These findings suggest that at moderate noise levels, listeners are able to adapt to dialect variation in the acoustic signal such that some cross-dialect intelligibility differences are neutralized, despite relatively poor explicit dialect classification performance. However, at more difficult noise levels, participants cannot effectively adapt to dialect variation in the acoustic signal and cross-dialect differences in intelligibility emerge for all listeners, regardless of their dialect.

Effects of open-set and closed-set task demands on spoken word recognition.

Closed-set tests of spoken word recognition are frequently used in clinical settings to assess the speech discrimination skills of hearing-impaired listeners, particularly children. Speech scientists have reported robust effects of lexical competition and talker variability in open-set tasks but not closed-set tasks, suggesting that closed-set tests of spoken word recognition may not be valid assessments of speech recognition skills. The goal of the current study was to explore some of the task demands that might account for this fundamental difference between open-set and closed-set tasks. In a series of four experiments, we manipulated the number and nature of the response alternatives. Results revealed that as more highly confusable foils were added to the response alternatives, lexical competition and talker variability effects emerged in closed-set tests of spoken word recognition. These results demonstrate a close coupling between task demands and lexical competition effects in lexical access and spoken word recognition processes.

The Nationwide Speech Project: A new corpus of American English dialects.

Perceptual and acoustic research on dialect variation in the United States requires an appropriate corpus of spoken language materials. Existing speech corpora that include dialect variation are limited by poor recording quality, small numbers of talkers, and/or small samples of speech from each talker. The Nationwide Speech Project corpus was designed to contain a large amount of speech produced by male and female talkers representing the primary regional varieties of American English. Five male and five female talkers from each of six dialect regions in the United States were recorded reading words, sentences, passages, and in interviews with an experimenter, using high quality digital recording equipment in a sound-attenuated booth. The resulting corpus contains nearly an hour of speech from each of the 60 talkers that can be used in future research on the perception and production of dialect variation.

Effects of region of origin and geographic mobility on perceptual dialect categorization.

Recent findings have shown that listeners' region of origin and geographic mobility affect their perception of dialect-specific properties of speech in vowel identification and dialect categorization tasks. The present study examined the perceptual dialect classification performance of four groups of listeners using a six-alternative forced-choice categorization task. The residential history of the listeners was manipulated so that the four groups of listeners differed in terms of region of origin (Northern or Midland United States) and geographic mobility (Mobile or Non-Mobile). Although residential history did not significantly affect accuracy in the categorization task, both region of origin and geographic mobility were found to affect the underlying perceptual similarity structure of the different regional varieties. Geographically local dialects tended to be confused more often than nonlocal dialects, although this effect was attenuated by geographic mobility.

Variation in the strength of lexical encoding across dialects.

Lexical processing is slower and less accurate for unfamiliar dialects than familiar dialects. The goal of the current study was to test the hypothesis that dialect differences in lexical processing reflect differences in lexical encoding strength across dialects. Lexical encoding (i.e., updating the cognitive lexical representation to reflect the current token) was distinguished from lexical recognition (i.e., mapping the incoming acoustic signal to the target lexical category) in a series of lexical processing tasks with Midland and Northern American English. The experiments were conducted in the Midland region with Midland and Northern listeners. The results confirmed differential processing of the two dialects: the Midland dialect was processed more quickly than the Northern dialect. The results further revealed significantly larger repetition benefits (i.e., priming) and cross-dialect lexical interference effects for lexical forms in the Midland dialect than in the Northern dialect for both listener groups, particularly when the stimulus materials were presented in noise. These results suggest that lexical information is more strongly encoded for the contextually-local Midland dialect than for the non-local Northern dialect. We interpret these effects as reflecting cognitive processing costs associated with normalization for dialect variation, which lead to weaker lexical encoding under more difficult processing conditions.

EFFECTS OF TALKER GENDER ON DIALECT CATEGORIZATION.

The identification of the gender of an unfamiliar talker is an easy and automatic process for naïve adult listeners. Sociolinguistic research has consistently revealed gender differences in the production of linguistic variables. Research on the perception of dialect variation, however, has been limited almost exclusively to male talkers. In the present study, naïve participants were asked to categorize unfamiliar talkers by dialect using sentence-length utterances under three presentation conditions: male talkers only, female talkers only, and a mixed gender condition. The results revealed no significant differences in categorization performance across the three presentation conditions. However, a clustering analysis of the listeners' categorization errors revealed significant effects of talker gender on the underlying perceptual similarity spaces. The present findings suggest that naïve listeners are sensitive to gender differences in speech production and are able to use those differences to reliably categorize unfamiliar male and female talkers by dialect.