Perception of indexical cues in speech by children and adults with and without dyslexia: Regional dialect and gender identification.

Auditory research in developmental dyslexia proposes that deficient auditory processing of speech underlies difficulties with reading and spelling. Focusing predominantly on phonological processing, studies have not yet addressed the role of the speaker-related (indexical) properties of speech that enable the formation of phonological representations. Here, we assess auditory processing of indexical characteristics cueing a speaker's regional dialect and gender to determine whether dyslexia constraints recognition of dialect features and voice gender. Adults and children aged 11-14 years with dyslexia and their age-matched controls responded to 360 unique sentences extracted from spontaneous conversations of 40 speakers. In addition to the original unprocessed speech, there were two focused filtered conditions (using lowpass filtering at 400 Hz and 8-channel noise vocoding) probing listeners' responses to segmental and prosodic cues. Compared with controls, both groups with dyslexia were significantly limited in their abilities to recognize dialect features from either set of cues. The results for gender suggest that their comparatively worse gender recognition in the noise-vocoded condition was possibly related to poor temporal resolution. We propose that the deficient processing of indexical cues by individuals with dyslexia originates in peripheral auditory processes, of which impaired processing of relevant temporal cues in amplitude envelope is a likely candidate.

Perception of local and non-local vowels by adults and children in the South.

This study assessed the ability of Southern listeners to accommodate extensive talker variability in identifying vowels in their local Appalachian community in the context of sound change. Building on prior work, the current experiment targeted a subset of spectrally overlapping vowels in local and two non-local varieties to establish whether adult and child listeners will demonstrate the local dialect advantage. Listeners responded to isolated target words, which minimized the interaction of multiple linguistic and dialect-specific features. For most vowel categories, the local dialect advantage was not demonstrated. However, adult listeners showed sensitivity to generational changes, indicating their familiarity with the local norms. A differential response pattern in children suggests that children perceived the vowels through the lens of their own experience with vowel production, representing a sound change in the community. Compared with the adults, children also relied more on stress cues, with increased confusions when the vowels were unstressed. The study provides evidence that identification accuracy is dependent upon the robustness of cues in individual vowel categories-whether local or non-local-and suggests that the bottom-up processes underlying phonetic vowel categorization in isolated monosyllables can interact with the top-down processing of dialect- and talker-specific information.

Differences in nasalance and nasality perception between Texas South and Midland dialects.

While previous research has primarily concerned the dialectal influence on speakers' production of oral-nasal balance, quantitatively represented by nasalance, information on cross-dialectal variation in nasality perception is limited. This study investigated the effects of speakers'/listeners' dialectal background on oral-nasal balance characteristics estimated by nasalance, as well as nasality perception measured by direct magnitude estimation with modulus. Represented by two geographically distinct regions, Texas South and Midland dialects were of special interest given that the two dialects lie at opposite ends of normal nasalance variation [Awan, Bressmann, Poburka, Roy, Sharp, and Watts. (2015). J. Speech Lang. Hear. Res. 58, 69-77]. Mean nasalance of various speech stimuli and direct magnitude estimation ratings on synthesized vowel stimuli with varying degrees of simulated nasalization were obtained from 62 participants (31 Texas South, 31 Midland). The results revealed that the two dialectal groups significantly differed in nasalance scores and nasality ratings, with Texas South exhibiting higher nasalance for standardized passage readings and assigning higher nasality ratings on the synthetic auditory stimuli than Midland. These findings indicate that, in addition to production variations of oral-nasal balance characteristics, perceptual variations of nasality exist at a dialectal level.

Effects of regional dialect on oral-nasal balance and nasality perception.

While cross-dialectal variations in nasalance have been investigated in previous studies, the influence of regional dialect on listeners' perceptual ratings of nasality has received limited research attention. This study explored cross-dialectal differences in the production of oral-nasal balance and the perception of nasality, with special emphasis on Inland North (IN) and Midland (M) dialects in the USA. Twenty-six adults representing the IN (n = 15) and M (n = 11) dialects participated in the study. Oral-nasal balance characteristics and nasality perception were compared between dialects using mean nasalance of various speech stimuli, measured via nasometry, and perceptual ratings of nasality of synthetic vowel stimuli, measured using direct magnitude estimation (DME). Despite similar mean nasalance scores between two regional dialects for standardized passage readings and sustained vowels, IN and M groups significantly differed in their perceptual ratings of nasality, with the DMEs of IN listeners being consistently and significantly higher, i.e. more nasal, than those of M listeners. Our findings provide evidence for perceptual variations of nasality that may exist at a dialectal level in addition to cross-linguistic variations in the perception of nasality as reported by Lee et al. (2008). Further research is needed to determine to what extent perceptual variations of nasality exist in other dialects and how these variations manifest in perceptual judgments of hypernasality and its severity ratings.

Regional Variation in Fundamental Frequency of American English Vowels.

We examined whether the fundamental frequency (f0) of vowels is influenced by regional variation, aiming to (1) establish how the relationship between vowel height and f0 ("intrinsic f0") is utilized in regional vowel systems and (2) determine whether regional varieties differ in their implementation of the effects of phonetic context on f0 variations. An extended set of acoustic measures explored f0 in vowels in isolated tokens (experiment 1) and in connected speech (experiment 2) from 36 women representing 3 different varieties of American English. Regional differences were found in f0 shape in isolated tokens, in the magnitude of intrinsic f0 difference between high and low vowels, in the nature of f0 contours in stressed vowels, and in the completion of f0 contours in the context of coda voicing. Regional varieties utilize f0 control in vowels in different ways, including regional f0 ranges and variation in f0 shape.

Reconceptualizing the vowel space in analyzing regional dialect variation and sound change in American English.

Vowel space area (VSA) calculated on the basis of corner vowels has emerged as a metric for the study of regional variation, speech intelligibility and speech development. This paper gives an evaluation of the basic assumptions underlying both the concept of the vowel space and the utility of the VSA in making cross-dialectal and sound change comparisons. Using cross-generational data from 135 female speakers representing three distinct dialects of American English, the first step was to establish that the vowel quadrilateral fails as a metric in the context of dialect variation. The next step was to examine the efficacy of more complete assessments of VSA represented by the convex hull and the concave hull. Despite the improvement over the quadrilateral, both metrics yielded inconsistent estimates of VSA. This paper then explores the possibility that regional variation can be characterized more effectively if formant dynamics and the resulting spectral overlap were also considered in defining the space. The proposed formant density approach showed that the working space may be common to all dialects but the differences are in the internal distribution of spectral density regions that define dialect-specific "usage" of the acoustic space. The dialect-inherent distribution of high and low density regions is largely shaped by sound change.

Dyslexia Limits the Ability to Categorize Talker Dialect.

Purpose: The purpose of this study was to determine whether the underlying phonological impairment in dyslexia is associated with a deficit in categorizing regional dialects. Method: Twenty adults with dyslexia, 20 school-age children with dyslexia, and 40 corresponding control listeners with average reading ability listened to sentences produced by multiple talkers (both sexes) representing two dialects: Midland dialect in Ohio (same as listeners' dialect) and Southern dialect in Western North Carolina. Participants' responses were analyzed using signal detection theory. Results: Listeners with dyslexia were less sensitive to talker dialect than listeners with average reading ability. Children were less sensitive to dialect than adults. Under stimulus uncertainty, listeners with average reading ability were biased toward Ohio dialect, whereas listeners with dyslexia were unbiased in their responses. Talker sex interacted with sensitivity and bias differently for listeners with dyslexia than for listeners with average reading ability. The correlations between dialect sensitivity and phonological memory scores were strongest for adults with dyslexia. Conclusions: The results imply that the phonological deficit in dyslexia arises from impaired access to intact phonological representations rather than from poorly specified representations. It can be presumed that the impeded access to implicit long-term memory representations for indexical (dialect) information is due to less efficient operations in working memory, including deficiencies in utilizing talker normalization processes.

Intrinsic fundamental frequency of vowels is moderated by regional dialect.

There has been a long-standing debate whether the intrinsic fundamental frequency (IF0) of vowels is an automatic consequence of articulation or whether it is independently controlled by speakers to perceptually enhance vowel contrasts along the height dimension. This paper provides evidence from regional variation in American English that IF0 difference between high and low vowels is, in part, controlled and varies across dialects. The sources of this F0 control are socio-cultural and cannot be attributed to differences in the vowel inventory size. The socially motivated enhancement was found only in prosodically prominent contexts.

Variation in Vowel Duration Among Southern African American English Speakers.

PURPOSE: Atypical duration of speech segments can signal a speech disorder. In this study, we examined variation in vowel duration in African American English (AAE) relative to White American English (WAE) speakers living in the same dialect region in the South to characterize the nature of systematic variation between the 2 groups. The goal was to establish whether segmental durations in minority populations differ from the well-established patterns in mainstream populations. METHOD: Participants were 32 AAE and 32 WAE speakers differing in age who, in their childhood, attended either segregated (older speakers) or integrated (younger speakers) public schools. Speech materials consisted of 14 vowels produced in hVd-frame. RESULTS: AAE vowels were significantly longer than WAE vowels. Vowel duration did not differ as a function of age. The temporal tense-lax contrast was minimized for AAE relative to WAE. Vowels produced by females were significantly longer than vowels produced by males for both AAE and WAE. CONCLUSIONS: African American speakers should be expected to produce longer vowels relative to White speakers in a common geographic area. These longer durations are not deviant but represent a typical feature of AAE. This finding has clinical importance in guiding assessments of speech disorders in AAE speakers.

The effects of indexical and phonetic variation on vowel perception in typically developing 9- to 12-year-old children.

PURPOSE The purpose of this study was to investigate how linguistic knowledge interacts with indexical knowledge in older children's perception under demanding listening conditions created by extensive talker variability. METHOD Twenty-five 9- to 12-year-old children, 12 from North Carolina (NC) and 13 from Wisconsin (WI), identified 12 vowels in isolated /hVd/ words produced by 120 talkers representing the 2 dialects (NC and WI), both genders, and 3 age groups (generations) of residents from the same geographic locations as the listeners. RESULTS Identification rates were higher for responses to talkers from the same dialect as the listeners and for female speech. Listeners were sensitive to systematic positional variations in vowels and their dynamic structure (formant movement) associated with generational differences in vowel pronunciation resulting from sound change in a speech community. Overall identification rate was 71.7%, which is 8.5% lower than for the adults responding to the same stimuli in Jacewicz and Fox (2012). CONCLUSION Typically developing older children were successful in dealing with both phonetic and indexical variation related to talker dialect, gender, and generation. They were less consistent than the adults, most likely because of less efficient encoding of acoustic-phonetic information in the speech of multiple talkers and relative inexperience with indexical variation.

The effects of cross-generational and cross-dialectal variation on vowel identification and classification.

Cross-generational and cross-dialectal variation in vowels among speakers of American English was examined in terms of vowel identification by listeners and vowel classification using pattern recognition. Listeners from Western North Carolina and Southeastern Wisconsin identified 12 vowel categories produced by 120 speakers stratified by age (old adults, young adults, and children), gender, and dialect. The vowels /ɝ, o, ʊ, u/ were well identified by both groups of listeners. The majority of confusions were for the front /i, ɪ, e, ɛ, æ/, the low back /ɑ, ɔ/ and the monophthongal North Carolina /aɪ/. For selected vowels, generational differences in acoustic vowel characteristics were perceptually salient, suggesting listeners' responsiveness to sound change. Female exemplars and native-dialect variants produced higher identification rates. Linear discriminant analyses which examined dialect and generational classification accuracy showed that sampling the formant pattern at vowel midpoint only is insufficient to separate the vowels. Two sample points near onset and offset provided enough information for successful classification. The models trained on one dialect classified the vowels from the other dialect with much lower accuracy. The results strongly support the importance of dynamic information in accurate classification of cross-generational and cross-dialectal variations.

Auditory spectral integration in the perception of static vowels.

PURPOSE: To evaluate potential contributions of broadband spectral integration in the perception of static vowels. Specifically, can the auditory system infer formant frequency information from changes in the intensity weighting across harmonics when the formant itself is missing? Does this type of integration produce the same results in the lower (first formant [F1]) and higher (second formant [F2]) regions? Does the spacing between the spectral components affect a listener's ability to integrate the acoustic cues? METHOD: Twenty young listeners with normal hearing identified synthesized vowel-like stimuli created for adjustments in the F1 region (/Λ/-/α/, /i/-/ε/) and in the F2 region (/Λ/-/æ/). There were 2 types of stimuli: (a) 2-formant tokens and (b) tokens in which 1 formant was removed and 2 pairs of sine waves were inserted below and above the missing formant; the intensities of these harmonics were modified to cause variations in their spectral center of gravity (COG). The COG effects were tested over a wide range of frequencies. RESULTS: Obtained patterns were consistent with calculated changes to the spectral COG, in both the F1 and F2 regions. The spacing of the sine waves did not affect listeners' responses. CONCLUSION: The auditory system may perform broadband integration as a type of auditory wideband spectral analysis.

Regional dialect variation in the vowel systems of typically developing children.

PURPOSE: To investigate regional dialect variation in the vowel systems of typically developing 8- to 12-year-old children. METHOD: Thirteen vowels in isolated h_d words were produced by 94 children and 93 adults (males and females). All participants spoke American English and were born and raised in 1 of 3 distinct dialect regions in the United States: western North Carolina (Southern dialect), central Ohio (Midland dialect), and southeastern Wisconsin (Northern Midwestern dialect). Acoustic analysis included formant frequencies (F1 and F2) measured at 5 equidistant time points in a vowel and formant movement (trajectory length). RESULTS: Children's productions showed many dialect-specific features comparable to those in adult speakers, both in terms of vowel dispersion patterns and formant movement. Different features were also found, including systemic vowel changes, significant monophthongization of selected vowels, and greater formant movement in diphthongs. CONCLUSIONS: The acoustic results provide evidence for regional distinctiveness in children's vowel systems. Children acquire not only the systemic relations among vowels but also their dialect-specific patterns of formant dynamics. Directing attention to the regional variation in the production of American English vowels, this work may prove helpful in better understanding and interpreting the development of vowel categories and vowel systems in children.

Cross-generational vowel change in American English.

This study examines cross-generational changes in the vowel systems in central Ohio, southeastern Wisconsin and western North Carolina. Speech samples from 239 speakers, males and females, were divided into three age groups: grandparents (66-91 years old), parents (35-51) and children (8-12). Acoustic analysis of vowel dynamics (i.e., formant movement) was undertaken to explore variation in the amount of spectral change for each vowel. A robust set of cross-generational changes in /ɪ, ε, æ, ɑ/ was found within each dialect-specific vowel system, involving both their positions and dynamics. With each successive generation, /ɪ, ε, æ/ become increasingly monophthongized and /ɑ/ is diphthongized in children. These changes correspond to a general anticlockwise parallel rotation of vowels (with some exceptions in /ɪ/ and /ε/). Given the widespread occurrence of these parallel chain-like changes, we term this development the "North American Shift" which conforms to the general principles of chain shifting formulated by Labov (1994) and others.

Auditory spectral integration in nontraditional speech cues in diotic and dichotic listening.

Underlying auditory processes in speech perception were explored. Specifically of interest were the stages of auditory processing involved in the integration of dynamic information in nontraditional speech cues such as the virtual formant transitions. These signals utilize intensity ratio cues and changes in spectral center-of-gravity (instead of the actual formant frequency transitions) to produce perceived F3 glides. 6 men and 8 women (M age = 24.2 yr., SD = 2.1), recruited through posted materials from graduate students at The Ohio State University, participated in two experiments. The results for frequency-based formant transitions (Exp. 1) indicated that spectral cues to syllable identification are combined at more central levels of auditory processing. However, when the components of the virtual formant stimuli were divided between the ears in a dichotic listening task (Exp. 2), the results indicated that auditory spectral integration may occur above the auditory periphery but at stages more intermediate rather than central.

Auditory spectral integration in the perception of diphthongal vowels.

This study considers an operation of an auditory spectral integration process which may be involved in perceiving dynamic time-varying changes in speech found in diphthongs and glide-type transitions. Does the auditory system need explicit vowel formants to track the dynamic changes over time? Listeners classified diphthongs on the basis of a moving center of gravity (COG) brought about by changing intensity ratio of static spectral components instead of changing an F2. Listeners were unable to detect COG movement only when the F2 change was small (160 Hz) or when the separation between the static components was large (4.95 bark).

Between-speaker and within-speaker variation in speech tempo of American English.

This study characterizes the speech tempo (articulation rate, excluding pauses) of two distinct varieties of American English taking into account both between-speaker and within-speaker variation. Each of 192 speakers from Wisconsin (the northern variety) and from North Carolina (the southern variety), men and women, ranging in age from children to old adults, read a set of sentences and produced a spontaneous unconstrained talk. Articulation rate in spontaneous speech was modeled using fixed-mixed effects analyses. The models explored the effects of the between-speaker factors dialect, age and gender and included each phrase and its length as a source of both between- and within-speaker variation. The major findings are: (1) Wisconsin speakers speak significantly faster and produce shorter phrases than North Carolina speakers; (2) speech tempo changes across the lifespan, being fastest for individuals in their 40s; (3) men speak faster than women and this effect is not related to the length of phrases they produce. Articulation rate in reading was slower than in speaking and the effects of gender and age also differed in reading and spontaneous speech. The effects of dialect in reading remained the same, showing again that Wisconsin speakers had faster articulation rates than did North Carolina speakers.

Cross-dialectal variation in formant dynamics of American English vowels.

This study aims to characterize the nature of the dynamic spectral change in vowels in three distinct regional varieties of American English spoken in the Western North Carolina, in Central Ohio, and in Southern Wisconsin. The vowels /I, epsilon, e, ae, aI/ were produced by 48 women for a total of 1920 utterances and were contained in words of the structure /bVts/ and /bVdz/ in sentences which elicited nonemphatic and emphatic vowels. Measurements made at the vowel target (i.e., the central 60% of the vowel) produced a set of acoustic parameters which included position and movement in the F1 by F2 space, vowel duration, amount of spectral change [measured as vector length (VL) and trajectory length (TL)], and spectral rate of change. Results revealed expected variation in formant dynamics as a function of phonetic factors (vowel emphasis and consonantal context). However, for each vowel and for each measure employed, dialect was a strong source of variation in vowel-inherent spectral change. In general, the dialect-specific nature and amount of spectral change can be characterized quite effectively by position and movement in the F1 by F2 space, vowel duration, TL (but not VL which underestimates formant movement), and spectral rate of change.

Acoustic and spectral patterns in young children's stop consonant productions.

The aim of this study was to examine the acoustic and spectral patterns of stop articulation in the speech of pre-pubescent children. A set of voiceless stop consonants, /ptk/, produced by a group of adults and typically developing children 3-5 years of age were examined in terms of multiple acoustic and spectral parameters. Findings indicated that, with the exception of spectral kurtosis, the acoustic and spectral characteristics of the stop productions varied significantly as a function of place of articulation and vowel context. Sex-specific differences in spectral slope, mean, and skewness were found for the 5-year-old and adult speakers. Such differences in adult speakers can be explained in part by variation in vocal tract size across the sex of the speaker; however, vocal tract dimorphism is typically not present in pre-pubescent children. Thus, the findings of this study provide some support that sex-specific differences in the speech patterns of young children may be associated with learned or behavioral factors, such as patterns of obstruent articulation that depend in part on a culturally determined male-female archetype.

Variation in stop consonant voicing in two regional varieties of American English.

This study is an acoustic investigation of the nature and extent of consonant voicing of the stop /b/ in two dialectal varieties of American English spoken in south-central Wisconsin and western North Carolina. The stop /b/ occurred at the juncture of two words such as small bids, in a position between two voiced sonorants, i.e. the liquid /l/ and a vowel. Twenty women participated, ten representing the Wisconsin and ten the North Carolina variety, respectively. Significant dialectal differences were found in the voicing patterns. The Wisconsin stop closures were usually not fully voiced and terminated in a complete silence followed by a closure release whereas North Carolina speakers produced mostly fully voiced closures. Further dialectal differences included the proportion of closure voicing as a function of word emphasis. For Wisconsin speakers, the proportion of closure voicing was smallest when the word was emphasized and it was greatest in non-emphatic positions. For North Carolina speakers, the degree of word emphasis did not have an effect on the proportion of closure voicing. The results suggest different mechanisms by which closure voicing is maintained in these two dialects, pointing to active articulatory maneuvers in North Carolina speakers and passive in Wisconsin speakers.