Covert Contrast Research Articles

Covert Contrast in Acquiring Fricatives by Preschool Children: Evidence From Najdi Arabic

Covert contrast is the statistically reliable distinction between target language phonemes produced in the process of language acquisition that is nevertheless not perceived by a native speaker of that language. This paper examines the acquisition of contrasts in four Najdi Arabic fricatives, /s/, /ʃ/, /θ/, and /ð/, and seeks to identify the most common substitutions in producing these sounds. Words were elicited from 25 preschool children (aged 3–5 years). The target words contained the studied fricative followed by either long /a:/ or short /a/ in the initial position. Praat software was used for acoustic analysis to extract the four acoustic cues: center of gravity, fricative noise duration, F1, and F2. Participants performed a word repetition task and a picture elicitation task. The results showed six cases of covert contrast, seven cases of no contrast, and 87 cases of accurate production (overt contrast). The results also revealed stopping, gliding, and affrication as substitutions in the manner of articulation, while replacement in place of articulation occurred in backing but most commonly in fronting (24 cases). The present study sought to determine implications for children’s linguistic performance, and, consequently, for language education and for planning treatment for children with speech disorders.

Are neutral roots in Uyghur really neutral? Evaluating a covert phonemic contrast

This paper looks at the case of so-called neutral roots in Uyghur (Turkic: China), whose idiosyncratic behavior with respect to the backness harmony system has been analyzed as stemming from a covert vowel contrast. Based on considerations of the structural properties of the language and the results of an experimental study, we suggest that an analysis based on lexical exceptionality is more parsimonious than the traditional analysis, unifying the treatment of neutral roots with other cases of exceptionality in the harmony system and accounting for a relationship between the patterning of roots and their frequency. We close by discussing implications for covert contrast analyses in general.

Covert contrasts and categorical perception: a comparison of two measurement tools

ABSTRACT This study considers adults’ perception of subtle differences in the error productions of /r/ and /l/ in young children. Given that these two phonemes share a common substitution [w], the potential covert contrast between these three sounds was investigated. The utility of two perceptual rating scales was compared: a linear visual analogue scale (VAS) and a triangular scale that considered the possibility of covert contrast among /r,l,w/. Adult listeners rated speech productions from children with cochlear implants (CIs) and speech age-matched children with normal hearing (NH) as they produced VCV or CV productions with /r,l,w/ in syllable-initial position. Mahalanobis distances of the listener ratings for each stimulus on each rating scale were calculated for analysis. Ultimately, there was no difference between the ratings of the two speaker populations. However, there was a significant difference in the amount of variability captured with each scale. The triangular scale reliably captured more variability in the productions than the linear VAS. The significant effect of scale type on the spread of listeners’ responses provides support for the claim that the type of rating system used can capture different aspects of a listener’s perceptions, thereby suggesting that the type of rating system used in a study may significantly influence that study’s findings.

Overt speech critically changes lateralization index and did not allow determination of hemispheric dominance for language: an fMRI study

BackgroundPre-surgical mapping of language using functional MRI aimed principally to determine the dominant hemisphere. This mapping is currently performed using covert linguistic task in way to avoid motion artefacts potentially biasing the results. However, overt task is closer to natural speaking, allows a control on the performance of the task, and may be easier to perform for stressed patients and children. However, overt task, by activating phonological areas on both hemispheres and areas involved in pitch prosody control in the non-dominant hemisphere, is expected to modify the determination of the dominant hemisphere by the calculation of the lateralization index (LI).ObjectiveHere, we analyzed the modifications in the LI and the interactions between cognitive networks during covert and overt speech task.MethodsThirty-three volunteers participated in this study, all but four were right-handed. They performed three functional sessions consisting of (1) covert and (2) overt generation of a short sentence semantically linked with an audibly presented word, from which we estimated the “Covert” and “Overt” contrasts, and a (3) resting-state session. The resting-state session was submitted to spatial independent component analysis to identify language network at rest (LANG), cingulo-opercular network (CO), and ventral attention network (VAN). The LI was calculated using the bootstrapping method.ResultsThe LI of the LANG was the most left-lateralized (0.66 ± 0.38). The LI shifted from a moderate leftward lateralization for the Covert contrast (0.32 ± 0.38) to a right lateralization for the Overt contrast (− 0.13 ± 0.30). The LI significantly differed from each other. This rightward shift was due to the recruitment of right hemispheric temporal areas together with the nodes of the CO.ConclusionAnalyzing the overt speech by fMRI allowed improvement in the physiological knowledge regarding the coordinated activity of the intrinsic connectivity networks. However, the rightward shift of the LI in this condition did not provide the basic information on the hemispheric language dominance. Overt linguistic task cannot be recommended for clinical purpose when determining hemispheric dominance for language.

Using ultrasound tongue imaging to study covert contrasts in second-language learners’ acquisition of English vowels

ABSTRACT Research attempting to understand the intermediate stages of first-language acquisition and disordered speech has led to the discovery of covert contrast. A covert contrast is a statistically reliable difference between phonemes that is produced by a language learner, but in a way that cannot be heard readily by a listener of the target language. In the present study, we aimed to extend the investigation of covert contrasts to the domain of second-language acquisition. In particular, we used ultrasound tongue imaging to examine whether adult second-language learners of American English produced articulatory distinctions between the target vowels, in addition to producing acoustic differences. We collected speech recordings from 21 speakers (7 Korean speakers, 7 Spanish speakers, 7 English controls) while they produced words illustrating the relevant vowel contrasts in English: /i/-/ɪ/ and /ɛ/-/æ/. Results showed that approximately 36% of our second-language participants implemented various patterns of covert contrast in vowel articulation. Ultrasound measurements revealed that two participants made a covert distinction between two vowels that were perceptually neutralized. For one participant, the anterior part of the tongue was higher for /i/ than /ɪ/, and for the other, it was higher for /ɛ/ than /æ/. Overall, our findings highlight the importance of a learner-oriented approach in studying the acquisition of phonemic contrasts and suggest that ultrasound tongue imaging can be a promising tool to examine the articulatory details of vowel production in second-language learners.

Treatment generalization from trained /ɹ/ to untrained /l/: a case study of persisting distortion errors

ABSTRACT The extent to which treatment of speech errors that are phonetic in nature (i.e., distortions) produces generalization to untrained sounds is not well understood. This case study reports a child referred for treatment of a velarized distortion of American English /ɹ/, who also demonstrated an inconsistent velarized distortion of /l/. Acoustic analysis revealed evidence of a covert contrast between /ɹ/ and /l/ prior to treatment. Ultrasound biofeedback treatment and perceptual training targeted /ɹ/ only, but progress was tracked for both /ɹ/ and /l/. Substantial improvements in perceptually rated accuracy and significant changes in acoustic features were observed for both sounds, indicating generalization. These results highlight that generalization from trained to untrained sounds is possible for children with residual speech errors characterized by phonetic distortions.

Overt speech feasibility using continuous functional magnetic resonance imaging: Isolation of areas involved in phonology and prosody.

To avoid motion artifacts, almost all speech-related functional magnetic resonance imagings (fMRIs) are performed covertly to detect language activations. This method may be difficult to execute, especially by patients with brain tumors, and does not allow the identification of phonological areas. Here, we aimed to evaluate overt task feasibility. Thirty-three volunteers participated in this study. They performed two functional sessions of covert and overt generation of a short sentence semantically linked with a word. Three main contrasts were performed: Covert and Overt for the isolation of language-activated areas, and Overt>Covert for the isolation of the motor cortical activation of speech. fMRI data preprocessing was performed with and without unwarping, and with and without regression of movement parameters as confounding variables. All types of results were compared to each other. For the Overt contrast, Dice coefficients showed strong overlap between each pair of types of results: 0.98 for the pair with and without unwarping, and 0.9 for the pair with and without movement parameter regression. The Overt>Covert contrast allowed isolation of motor laryngeal activations with high statistical reliability and revealed the right-lateralized temporal activity related to acoustic feedback. Overt speaking during magnetic resonance imaging induced few artifacts and did not significantly affect the results, allowing the identification of areas involved in primary motor control and prosodic regulation of speech. Unwarping and motion artifact regression in the postprocessing step, seem to not be necessary. Changes in lateralization of cortical activity by overt speech shall be explored before using these tasks for presurgical mapping.

Perception of Sibilants by Preschool Children With Overt and Covert Sound Contrasts.

Purpose This study explores the role of overt and covert contrasts in speech perception by children with speech sound disorder (SSD). Method Three groups of preschool-aged children (typically developing speech and language [TD], SSD with /s/~/ʃ/ contrast [SSD-contrast], and SSD with /s/~/ʃ/ collapse [SSD-collapse]) completed an identification task targeting /s/~/ʃ/ minimal pairs. The stimuli were produced by 3 sets of talkers: children with TD, children with SSD, and the participant himself/herself. We conducted a univariate general linear model to investigate differences in perception of tokens produced by different speakers and differences in perception between the groups of listeners. Results The TD and SSD-contrast groups performed similarly when perceiving tokens produced by themselves or other children. The SSD-collapse group perceived all speakers more poorly than the other 2 groups of children, performing at chance for perception of their own speech. Children who produced a covert contrast did not perceive their own speech more accurately than children who produced no identifiable acoustic contrast. Conclusion Preschool-aged children have not yet developed adultlike phonological representations. Collapsing phoneme production, even with a covert contrast, may indicate poor perception of the collapsed phonemes.

Covert contrasts in the acquisition of English high front vowels by native speakers of Korean, Portuguese, and Spanish

ABSTRACTThe purpose of this article is to report results of an investigation into the production of a covert contrast by native speakers of Korean, Portuguese, and Spanish in the acquisition of the English distinction between the high front vowels /i/ and /ɪ/. A covert contrast is a statistically reliable acoustic distinction made by a language learner between target-language phonemes that is nevertheless not perceived by native speakers of the target language. We gathered data on both the production and perception of this vowel contrast from a total of 36 second-language learners from the three native-language backgrounds, along with data from an additional 22 native-speaker controls. The findings are that about two-thirds of our second-language learners produced a covert contrast between the targeted vowel phonemes. In light of the results from research on child language acquisition and disordered speech, our data suggest that a covert contrast is not limited to the domain of the acquisition of a first language, either by normally developing children or by those with speech disorders.

Covert contrast and covert errors in persistent velar fronting

ABSTRACTAcoustic and articulatory studies demonstrate covert contrast in perceptually neutralised phonemic contrasts in both typical children and children with speech disorders. These covert contrasts are thought to be relatively common and symptomatic of phonetic speech disorders. However, clinicians in the speech therapy clinic have had no easy way of identifying this covertness. This study uses ultrasound tongue imaging to compare tongue contours for /t/and /k/in seven children with persistent velar fronting. We present a method of overlaying tongue contours to identify covert contrast at the articulatory level. Results show that all seven children, contrary to expectations, produced both /t/and /k/with near-identical tongue shapes showing no evidence of covert contrast. However, further analysis of one of the participants showed highly variable tongue shapes for /t/and /k/, including retroflex productions of both. Although not phonologically conditioned, this covert error is evidence of speech disorder at the phonetic level.

Gradient perception of children’s productions of /s/ and /θ/: A comparative study of rating methods

ABSTRACTPast studies have shown incontrovertible evidence for the existence of covert contrasts in children’s speech, i.e. differences between target productions that are nonetheless transcribed with the same phonetic symbol. Moreover, there is evidence that these are relevant to forming prognoses and tracking progress in children with speech sound disorder. A challenge remains to determine the most efficient and reliable methods for assessing covert contrasts. This study investigates how readily listeners can identify covert contrasts in children’s speech when using a continuous rating scale in the form of a visual analogue scale (VAS) to denote children’s productions. Individual listeners’ VAS responses were found to correlate statistically significantly with a variety of continuous measures of children’s production accuracy, including judgements of binary accuracy pooled over a large set of listeners. These findings reinforce the growing body of evidence that VAS judgements are potentially useful clinical measures of covert contrast.

Finding the experts in the crowd: Validity and reliability of crowdsourced measures of children’s gradient speech contrasts

ABSTRACTPerceptual ratings aggregated across multiple nonexpert listeners can be used to measure covert contrast in child speech. Online crowdsourcing provides access to a large pool of raters, but for practical purposes, researchers may wish to use smaller samples. The ratings obtained from these smaller samples may not maintain the high levels of validity seen in larger samples. This study aims to measure the validity and reliability of crowdsourced continuous ratings of child speech, obtained through Visual Analog Scaling, and to identify ways to improve these measurements. We first assess overall validity and interrater reliability for measurements obtained from a large set of raters. Second, we investigate two rater-level measures of quality, individual validity and intrarater reliability, and examine the relationship between them. Third, we show that these estimates may be used to establish guidelines for the inclusion of raters, thus impacting the quality of results obtained when smaller samples are used.

Electropalatographic (EPG) evidence of covert contrasts in disordered speech

ABSTRACTThe phenomenon of covert contrasts has intrigued researchers and clinicians since it was first identified using instrumental data nearly 50 years ago. The term covert contrast refers to phonological contrasts that listeners do not readily identify and which therefore pass unrecorded in transcription-based studies. Covert contrasts are viewed as significant from theoretical and clinical perspectives. Although influential, there are relatively few instrumental studies of covert contrasts. The studies that do exist are limited to revealing contrasts that manifest in specific phonetic parameters or phonological processes. However, recent studies have provided convincing new evidence that covert contrasts are likely to be widespread in child speech. The purpose of this article is threefold: to review electropalatography (EPG) studies of covert contrasts; to provide EPG examples from the speech of individuals with speech disorders and to discuss the implications in child speech.

Overt and covert contrast in L2 phonology.

This paper reports results on the acquisition of the English /p/ - /b/ contrast by native speakers of Arabic. This contrast does not exist in the participants' native language (NL). The central finding of this study is that some of the research participants exhibited a covert contrast between these segments in their interlanguage productions. That is, two of the five Arabic-speaking participants who were transcribed as having no contrast between [p] and [b] did, in fact, produced a statistically reliable distinction in voice onset time lags between the two target segments. The existence of such an intermediate stage of covert contrast in the learning of L2 phonology is eminently plausible, in view of the progressive nature of phonological acquisition. Our results help bring the learning of second-language contrasts into conformity with findings of the same phenomenon in the areas of L1 acquisition and phonologically disordered speech.

Covert contrast in velar fronting: An acoustic and ultrasound study

ABSTRACTThere is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralised. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralised the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed in this article.

ESTABELECIMENTO DO CONTRASTE ENTRE AS FRICATIVAS POR CRIANÇAS COM TRANSTORNO FONOLÓGICO: MANIPULAÇÃO DE PISTAS ACÚSTICAS

O presente trabalho versa sobre a presença de contrastes encobertos na fala de crianças com transtorno fonológico. A hipótese perseguida é a de que as crianças com transtorno fonológico se ancoram em pistas acústicas secundárias na tentativa de estabelecer contrastes fônicos da língua. Para tanto, foram utilizadas cinco gravações em áudio, advindas de cinco crianças entre 4 e 5 anos com transtorno fonológico, que apresentavam as chamadas “substituições fônicas” envolvendo a classe de sons das fricativas. Os dados foram editados e analisados com o uso do software PRAAT. Foi realizada uma transcrição fonética da primeira repetição (R1) de cada criança, por três juízes, e considerada a concordância de 66%. A partir dessa transcrição, foi realizada a análise fonológica contrastiva acústica de todas as “substituições” envolvendo a classe de sons das fricativas, a partir de seis parâmetros. Verificou-se a existência de contrastes encobertos nas produções tidas como homófonas auditivamente, representando um total de 54% do total das “substituições” identificadas pelos juízes. As crianças com transtorno fonológico ancoram-se preferencialmente em pistas acústicas secundárias na tentativa de distinguir os fones fricativos. Os dados obtidos neste estudo permitem reflexão acerca da importância de se considerar o detalhe fonético no interior dos modelos fonológicos.

Quasi-neutralization in the acquisition of English coronal fricatives by native speakers of Japanese

Second language learners show various forms of mispronunciation, or modification, of target pronunciation, most perhaps due to direct native language transfer, but others, summarized here, to deflected contrast, hypercorrection and covert contrast. The present paper reports on a novel form of adaptation that we term ‘quasi-neutralization,’ in which acoustic characteristics of competing target phonemes are found within the same interlanguage segment (e.g., think [θɪŋk] pronounced as [θsiŋk]). The three English voiceless coronal fricatives /s/, /ʃ/, /θ/ were elicited from Japanese learners of English via two techniques: a wordlist reading task that encouraged participants to focus on their pronunciation, and a sentence construction task that diverted their attention from pronunciation. Among different types of modification, quasi-neutralization was observed predominantly when participants were conscious of their pronunciation, which could reflect their linguistic insecurity as learners. This research thus illuminates another of the strategies that learners employ in the acquisition of L2 pronunciation.

Covert contrast in child phonology is not necessarily extragrammatical

Covert contrast in child phonology is not necessarily extragrammatical

Developing acoustic measures to evaluate the emergence of phonological contrast.

Acoustic analysis has been used in studying phonological development since at least the 1960s when Preston and colleagues measured voice onset time (VOT) in English- and Arabic-learning toddlers. Studies applying measures such as VOT, for stop voicing, and spectral peak frequency, for fricative place, show that the emergence of robust phonemic contrast is more gradual than it seems when phonetic transcription is used alone. For example, Japanese-speaking children’s short-lag productions of target /d/ labeled as “[t]” might show somewhat shorter VOT than their productions of target /t/. Studies that supplement acoustic measures with continuous labeling tasks, such as a visual analog scale with “d” and “t” as target endpoints, support the idea that not only is this developmental phenomenon of “covert contrast” ubiquitous, the associated subphonemic variation can be perceived by adult listeners given the appropriate task. Moreover, listeners with different kinds of experience with young children have different sensitivities to this acoustic variation. This finding suggests that appropriate acoustic measures can be developed to provide psychometrically valid measures over the full course of development from initial stages of producing undifferentiated or inappropriate cues to producing the adult community pattern for the contrast. [Work supported by NIDCD grant 02932 and NSF grants BSC-0729306, BSC-0729140, and BCS-0729277.]

Contraste fônico encoberto entre /t/ e /k/: um estudo de caso de normalidade e de transtorno fonológico

OBJETIVO: investigar, com auxílio de análise acústica, o estabelecimento do contraste fonológico de produções de um sujeito com transtorno fonológico que apresenta neutralização (pela análise de oitiva) do contraste entre as oclusivas alveolar e velar. MÉTODOS: foram analisadas as produções das oclusivas /t/ e /k/ combinadas com as vogais /a/ e /u/ na posição acentuada em dois sujeitos - com e sem transtorno fonológico - ambos do sexo masculino, com faixa etária entre 5 e 6 anos. Os parâmetros fonético-acústicos analisados incluíram a inspeção acústica da forma de onda, os parâmetros relativos às características espectrais do burst; os parâmetros acústicos relativos às características acústicas das vogais adjacentes às oclusivas e os parâmetros acústicos relativos ao padrão temporal. RESULTADOS: nas produções da criança com transtorno fonológico observou-se a presença de contrastes encobertos entre as oclusivas investigadas, marcadas tanto pelo uso inadequado quanto pelo correto das pistas fonéticas, mas com valores insuficientes. Nas produções da criança sem transtorno fonológico observou-se o uso de pelo menos uma pista fonética relativa às principais características de um segmento oclusivo que, com magnitude suficiente, propicia o resgate do contraste entre /t/ e /k/ pelos ouvintes. Nas produções de ambos os sujeitos as pistas fonéticas foram dependentes do contexto vocálico. CONCLUSÃO: um determinado contraste fônico pode ser entendido como uma constelação de pistas fonéticas que variam em sua interdependência e significância perceptual.