Vowel Intelligibility Research Articles

Acoustic measurements and intelligibility of English vowels produced by Thai speakers

Effective English communication across different languages and cultures has become increasingly important in a globalised world. To gain a deeper understanding of the segmental features of Thai speakers of English, this study aims to investigate the production of English monophthongs and diphthongs by Thai speakers and examine how intelligible their pronunciations are to others. Data were collected through two tasks: a production task and a listening task. For the production task, three Thai female speakers were chosen as the participants. They were recorded reading a passage consisting of all targeted vowels, and a total of 180 English tokens were analysed. For the listening task, thirty Malaysian listeners were asked to evaluate the speech intelligibility of the English sounds produced by the three speakers. The duration and formant frequencies of English vowels produced were measured to investigate the characteristics of the monophthongs and diphthongs. The findings show that there were significant differences in the durations between long and short vowels of the monophthongs, but there were no significant differences in the vowel quality produced. The ROC (rate of change) of formant frequencies (F1 and F2) indicates that there was no formant movement for the diphthongs /eɪ/, /əʊ/, and /eə/. The three diphthongs showed similar characteristics as other ASEAN Englishes that are monophthongal as /e:/, /o:/, and /ɛ:/, respectively. These findings confirm that speakers’ L1 influences English vowel production. Although there were vowel variations in the characteristics of the vowels produced by the speakers, the intelligibility scores were high.

Vowels in clear and conversational speech: Intelligibility for listeners with hearing loss

While my research during the past two decades has explored numerous perceptual properties of clear versus conversational speech, it all began with vowel intelligibility. In this presentation, I review my research on vowel intelligibility in listeners with hearing loss and whether and how it changes when talkers adopt a clear speaking style. I also discuss acoustic properties that may explain these changes and the potential interaction between clear speech acoustic properties and listener hearing status.

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.

Comparison of Vowel and Sentence Intelligibility in People With Dysarthria Secondary to Amyotrophic Lateral Sclerosis.

In this study, we examined the utility of vowel intelligibility testing for assessing the impact of dysarthria on speech characteristics in people with amyotrophic lateral sclerosis (ALS). We tested the sensitivity and specificity of overall vowel identification, as well as that of vowel-specific identification, to dysarthria presence and severity. We additionally examined the relationship between vowel intelligibility and sentence intelligibility. Twenty-three people with ALS and 22 age- and sex-matched control speakers produced sentences from the Speech Intelligibility Test (SIT), as well as 10 American English monophthongs in /h/-vowel-/d/ words for the vowel intelligibility test (VIT). Data for SIT and VIT scores came from 135 listeners. Diagnostic accuracy of VIT measures was evaluated using the area under the curve of receiver operator characteristics. We then examined differences between control speakers, speakers with mild dysarthria, and speakers with severe dysarthria in their relationship between SIT and VIT scores. The results suggest that the overall vowel intelligibility score showed high sensitivity and specificity in differentiating between speakers with and without dysarthria, even those with milder symptoms. In addition, single-vowel identification scores showed at least acceptable group differentiation between the mild and severe dysarthria groups, though fewer single vowels were acceptable discriminators between the control group and the group with mild dysarthria. Identification accuracy of /ɪ/ in particular showed excellent discrimination across all groups. Examination of the relationship between SIT and VIT scores suggests a severity-specific relationship. Speakers with SIT scores above 70% generally had higher SIT than VIT scores, whereas speakers with SIT below 70% generally had higher VIT than SIT scores. Vowel intelligibility testing can detect speech impairments in speakers with mild dysarthria and residual articulatory function in speakers with severe dysarthria. Vowel intelligibility testing may, therefore, be a useful addition to intelligibility testing for individuals with dysarthria.

Effect of visual information on vowel intelligibility in Japanese singing

Effect of visual information on vowel intelligibility in Japanese singing

An Investigation into the Vowel Space Area and Vowel Intelligibility among English-speaking Children with Cochlear Implant in India

Abstract Background: Literature does show that studies of the vowel space area (VSA) can be helpful to know speech production skills in children with hearing impairment (HI) cochlear implant (CI). The need for the present study was to investigate speech production skills among children with CI, who receive Aural Rehab in nonnative language, i.e., English. The VSA offers an easy quick way to compare speech production accuracy among them to typically developing chidlren (TDC) peer group. Aim of the Study: The study aimed at investigating the VSA in F2 versus F1 space formed by vowels /a/, /i/, and /u/ in two groups of children (typically developing [TD] and children with CIs) and the intelligibility of the vowels spoken in the consonant-vowel-consonant (CVC) contexts. Methods: Two groups of subjects participated in the study, 100 children with CIs and 200 age-matched typically developing children. Recordings of vowels /a/, /i/, and /u/ in CVC were used for formant frequency extraction using Praat software, and the VSA was calculated. The recorded utterances were presented to three judges, for the estimation of the percentage of correct responses for identifying the vowel. The VSA for the vowels and the intelligibility scoring in percentage were valuated. Results: The results showed that the VSA among children with CI was significantly less compared to TDC. The reduced VSA represents limited articulatory movement in children with CI compared to children with TD for primary vowels embedded in CVC syllables. The vowel intelligibility for the three vowels in the CVC context was reduced for children with CI (70%) compared to that of children with TDC (95%). Discussion: Both first- and second-formant frequencies show distinct differences between both groups and consequently in the VSA. F1 is lower for /a/ for the CI group, while it is higher for vowel /i/ and /u/ for the CI group compared to the TDC group, while F2, the values were lower for /i/ but elevated significantly for both /a/ and /u/ compared to children in TDC. The intelligibility of their utterances (CVC) of children with CI was lower than that of TDC. Since the children were age- and gender-matched and were nonnative speakers of English, linguistic influences on measured values were minimum. Reasons for changed formant frequencies have to be explored further in terms of the influence of rehabilitation methods, visibility of articulatory movements required, and formant information coded by speech coding strategies. Correlation studies of the VSA and the speech intelligibility measures may assist in therapy outcomes and improve speech intelligibility in children with HI and modifications to mapping strategies employed. Conclusion: The F1 is lower for /a/ for the CI group, while it is higher for vowel /i/ and /u/ for the CI group compared to the TDC group, while F2, the values were lower for /i/ but elevated significantly for both /a/ and /u/ compared to children in TDC. The vowel triangle area was reduced in the speech of CI group subjects compared to that of the group of TDC.

Investigating the Efficacy of Using Online Resources for Production Training in Learning Non-Native Vowel Contrasts

The current study investigates the benefits of virtual phonetic training on second language (L2) vowel production and examines whether production training improves perception. While the benefits of production instructions were investigated with instructions that were delivered by either a virtual or a face-to face teacher, a few studies investigated the benefits of online resources for second language (L2) learning with tutor audio instructions and feedback. Fifty-five Arabic speakers (21 served as a control group) took part in 3 one-to-one training sessions and were trained on producing seven Standard Southern British English (SSBE) vowels (/ ɪ, ɛ, ʌ, ɑː, ɔː, ɒ, ʊ/) that have been found to be difficult for Arabic learners of English. Improvements were assessed by their vowel identification, category discrimination accuracy and their vowel intelligibility. The results showed some improvements in vowel intelligibility and that vowel learning paved the way for improvement in perception, relative to the control group. The results indicate that using web-based tools along with audio instructions are beneficial for L2 learners and confirmed previous findings about the relationship between improvement in speech perception and production.

Intelligibility of speech produced by sighted and blind adults.

PurposeIt is well known that speech uses both the auditory and visual modalities to convey information. In cases of congenital sensory deprivation, the feedback language learners have access to for mapping visible and invisible orofacial articulation is impoverished. Although the effects of blindness on the movements of the lips, jaw, and tongue have been documented in francophone adults, not much is known about their consequences for speech intelligibility. The objective of this study is to investigate the effects of congenital visual deprivation on vowel intelligibility in adult speakers of Canadian French.MethodTwenty adult listeners performed two perceptual identification tasks in which vowels produced by congenitally blind adults and sighted adults were used as stimuli. The vowels were presented in the auditory, visual, and audiovisual modalities (experiment 1) and at different signal-to-noise ratios in the audiovisual modality (experiment 2). Correct identification scores were calculated. Sequential information analyses were also conducted to assess the amount of information transmitted to the listeners along the three vowel features of height, place of articulation, and rounding.ResultsThe results showed that, although blind speakers did not differ from their sighted peers in the auditory modality, they had lower scores in the audiovisual and visual modalities. Some vowels produced by blind speakers are also less robust in noise than those produced by sighted speakers.ConclusionTogether, the results suggest that adult blind speakers have learned to adapt to their sensory loss so that they can successfully achieve intelligible vowel targets in non-noisy conditions but that they produce less intelligible speech in noisy conditions. Thus, the trade-off between visible (lips) and invisible (tongue) articulatory cues observed between vowels produced by blind and sighted speakers is not equivalent in terms of perceptual efficiency.

Variability in L2 Vowel Production: Different Elicitation Methods Affect Individual Speakers Differently.

Elicitation methods are known to influence second language speech production. For teachers and language assessors, awareness of such effects is essential to accurate interpretations of testing outcomes. For speech researchers, understanding why one method gives better performance than another may yield insights into how second-language phonological knowledge is acquired, stored, and retrieved. Given these concerns, this investigation compared L2 vowel intelligibility on two elicitation tasks and determined the degree to which differences generalized across vowels, vowels in context, lexical items, and individual speakers. The dependent variable was the intelligibility of Cantonese speakers' productions of English /i I u ℧/ in varying phonetic environments. In a picture-naming task, the speakers produced responses without an auditory prompt. In a second task–interrupted repetition–they heard exemplars of the same targets without pictures, and repeated each one after counting aloud to 10, a step intended to disrupt their short-term auditory store and therefore prevent simple mimicry. For target words with scores below 80% on picture naming, mean intelligibility was more than 10 points higher on interrupted repetition. However, that difference did not generalize across conditions or across speakers. Thus, although it is technically accurate to say that, on average, interrupted repetition yielded better vowel intelligibility than did picture naming, that observation requires a great deal of qualification, particularly because of individual speaker differences. The outcomes are interpreted in terms of their relevance to language assessment and phonetic learning.

The relationship between perceived speech clarity and dysphonia: Preliminary investigation

Perceived listener ratings of sentence “clarity” have been used in studies involving clear speech and have been shown to demonstrate a strong correlation with vowel intelligibility as well as a robust clear speech effect (Ferguson and Kerr, 2009; Ferguson and Morgan, 2018). However, it remains unclear what aspects of the speech signal listeners are using to form their perception of speech clarity. It is possible that disruptions in the voice source (i.e., poor voice quality) affect listeners’ perception of clarity. Given the increased prevalence of dysphonia in elderly adults (a target population for clear speech), it is important to determine whether voice quality negatively affects perceptions of speech clarity. The current study aims to examine the relationship between perceived sentence clarity and acoustic and perceptual measures of voice quality. Eighty sentences produced by 10 female talkers (5 healthy young adults and 5 older adults with hearing loss) already rated for perceived clarity by young adult listeners will be analyzed in terms of acoustic measures of voice quality (CPPS, HNR, percent glottal fry, and spectral slope) and perceptual measures of voice quality (CAPE-V evaluation performed by two speech-language pathologists with training in voice disorders).

Perceptual clustering of high-pitched vowels in Chinese Yue Opera

Numerous studies on Western Opera singing have shown that listeners’ vowel identification performance decreases with an increasing fundamental frequency (fo). This study explores the intelligibility of high-pitched vowels in Yue Opera, the largest dialectal opera in China. Six long vowels (/i y e a o u/) were recorded by a professional female singer at ten fos between 220 and 932 Hz, of which 700-ms nuclei with flat fo contours and resonance trajectories were extracted as stimuli. In a within-subject design, sixteen phonetically trained listeners responded on a free-choice vowel quadrilateral (task 1) and in a two-alternative forced-choice task (task 2) to indicate which vowel was presented. Results show that vowels cluster in the perceptual space into three groups (/i y e/, /u o/, /a/) above 521 Hz and that listeners could identify vowels between but not within groups with high accuracy up to at least 932 Hz. Multidimensional scaling (MDS) of simulated auditory excitation patterns reveals highly differentiable spectral shapes between groups. These findings put into question whether previous results on Western Opera could be generalized to other forms of opera singing.

Intelligibility of dysphonic speech in auralized classrooms.

Voice disorders can reduce the speech intelligibility of affected speakers. This study evaluated the effect of noise, voice disorders, and room acoustics on vowel intelligibility, listening easiness, and the listener's reaction time. Three adult females with dysphonia and three adult females with normal voice quality recorded a series of nine vowels of American English in /h/-V-/d/ format (e.g., "had"). The recordings were convolved with two oral-binaural impulse responses acquired from measurements in two classrooms with 0.4 and 3.1 s of reverberation time, respectively. The stimuli were presented in a forced-choice format to 29 college students. The intelligibility and the listening easiness were significantly higher in quiet than in noisy conditions, when the speakers had normal voice quality compared to a dysphonic voice, and in low reverberated environments compared to high reverberated environments. The response time of the listener was significantly longer for speech presented in noisy conditions compared to quiet conditions and when the voice was dysphonic compared with healthy voice quality.

Recalling vowel sequences in completing backgrounds: Effects of rhythmic regularity and tempo

Previous studies have demonstrated that the rhythmic regularities embedded in naturally produced speech are essential for speech understanding in the presence of competing backgrounds. In the current study, the facilitative effect of rhythmic regularity was further investigated using a vowel-recall task. Listeners recalled the last three vowels from a sequence of 9 to 18 synthetic vowels presented at an average rate of 2 vowels/second along with a competing sequence of harmonic complexes. Through this task, the rhythmic regularity (isochronous or anisochronous) and tempo of the target and competitor sequences as well as the duration of exposure to target rhythmic context (i.e., the target sequence length) were independently manipulated without affecting the intelligibility of individual target vowels. Better recall performance was found for isochronous target sequences compared to anisochronous target sequences and with longer exposure to the rhythmic context prior to recall. The rhythmic regularity of the competing signal had no significant effect on recall performance; however, the tempo of the competing signal was significant with recall performance improving as the background tempo increased from 1 to 4 vowels/second. These effects of rhythm and tempo are consistent with theories of selective listening based on attentional entrainment.

On the Difficulty of Defining “Difficult” in Second-Language Vowel Acquisition

Hierarchies of difficulty in second-language (L2) phonology have long played a role in the postulation and evaluation of learning models. In L2 pronunciation teaching, hierarchies are assumed to be helpful in the development of instructional strategies based on anticipated areas of difficulty. This investigation addressed the practicality of defining a pedagogically useful hierarchy of difficulty for English tense and lax close vowels (/i I u ʊ/) produced by Cantonese speakers. Unlike their English counterparts, Cantonese close tense-lax pairs are allophonic variants with [i u] occurring before alveolars and [I ʊ] before velars. Each tense-lax pair represents a “phonemic split” in which members of a single L1 category are realized contrastively in L2. Despite evidence that English tense-lax distinctions are challenging for Cantonese speakers, no previous empirical work has closely considered the problem from the standpoint of vowel intelligibility across multiple phonetic contexts and in different words sharing the same rhyme. In a picture-based word-elicitation task, 18 Cantonese-speaking participants produced 31 high-frequency CV and CVC words. Vowels were evaluated for intelligibility by phonetically-trained judges. A series of mixed-effects binary logistic models were fitted to the scores, with vowel quality, phonetic context (rhyme) and word as factors, and length of Canadian residence and daily use of English as co-variates. As expected, the general hierarchy of difficulty for vowels that emerged (/i/ > /u/ > /ʊ/ > /I/) was complicated by large differences across phonetic contexts. Results were not readily explicable in terms of transfer; moreover, different words with the same rhyme were not produced with equal intelligibility. The most serious modeling complication was the sizeable inter-speaker variability in difficulties, which could not be accounted for by model co-variates. Although some difficulties were roughly systematic at the group level, it is argued that establishing a pedagogically useful hierarchy on such data would prove intractable. Rather, L2 learners might be better served by assessment and instructional targeting of their individual problem areas than by a focus on errors predicted from hierarchies of difficulty.

Brief Report: Autistic Traits Predict Spectral Correlates of Vowel Intelligibility for Female Speakers.

A growing body of research finds that neurotypical autistic traits are predictive of speech perception and language comprehension patterns, but considerably less is known about the influence of these traits on speech production. In this brief report, we present an analysis of vowel productions from 74 American English speakers who participated in a communicative speaking task. Results show higher autistic trait load to be broadly and inversely related to spectral correlates of vowel intelligibility. However, the statistical significance of this relationship is specific to autistic traits along the pragmatic communication dimension, and limited to female speakers.

Effect of voice problems on vowel identifications in different acoustics environments

Voice disorders can reduce speech intelligibility. This study evaluated the effect of noise, voice disorders, and room acoustics on vowel intelligibility. College students listened to 9 vowels in /h/-V-/d/ format. The speech was recorded by three adult females with dysphonia and three adult females with normal voice quality. The recordings were convolved with three oral-binaural impulse responses with 0.4 s, 0.7 s, and 3.1 s of reverberation time. The test was performed online. The intelligibility and the listening easiness were significantly higher when the speakers had normal voice quality and in low reverberated environments.

Vowel Production in Prelingually Deafened Mandarin-Speaking Children With Cochlear Implants

Purpose The purpose of this study was to characterize the acoustic profile and to evaluate the intelligibility of vowel productions in prelingually deafened, Mandarin-speaking children with cochlear implants (CIs). Method Twenty-five children with CIs and 20 age-matched children with normal hearing (NH) were recorded producing a list of Mandarin disyllabic and trisyllabic words containing 20 Mandarin vowels [a, i, u, y, ɤ, ɿ, ʅ, ai, ei, ia, ie, ye, ua, uo, au, ou, iau, iou, uai, uei] located in the first consonant-vowel syllable. The children with CIs were all prelingually deafened and received unilateral implantation before 7 years of age with an average length of CI use of 4.54 years. In the acoustic analysis, the first two formants (F1 and F2) were extracted at seven equidistant time locations for the tested vowels. The durational and spectral features were compared between the CI and NH groups. In the vowel intelligibility task, the extracted vowel portions in both NH and CI children were presented to six Mandarin-speaking, NH adult listeners for identification. Results The acoustic analysis revealed that the children with CIs deviated from the NH controls in the acoustic features for both single vowels and compound vowels. The acoustic deviations were reflected in longer duration, more scattered vowel categories, smaller vowel space area, and distinct formant trajectories in the children with CIs in comparison to NH controls. The vowel intelligibility results showed that the recognition accuracy of the vowels produced by the children with CIs was significantly lower than that of the NH children. The confusion pattern of vowel recognition in the children with CIs generally followed that in the NH children. Conclusion Our data suggested that the prelingually deafened children with CIs, with a relatively long duration of CI experience, still showed measurable acoustic deviations and lower intelligibility in vowel productions in comparison to the NH children.

Vowel Modification (Aggiustamento) in Soprano Voices

Singers convey meaning via both text and music. As sopranos balance tone quality and diction, vowel intelligibility is often compromised at high pitches. This study examines how sopranos modify their vowels against an increasing fundamental, and in turn how such vowel modification affects vowel intelligibility. We examine the vowel modification process of three non-central vowels in Cantonese ([a], [ɛ] and [ɔ]) using the spectral centroid. Acoustic results suggest that overall vowel modification is conditioned by vowel height in mid-ranges and by vowel frontness in higher ranges. In a following perception task, listeners identified and discriminated vowels at pitches spanning an octave from A4 (nominally 440 Hz) to G♯5 (nominally 831 Hz). Results showed that perceptual accuracy rates of the three vowels’ match their acoustic patterns. The overall results suggest that vowels are not modified in a unified way in sopranos’ voices, implying that research on sopranos’ singing strategies should consider vocalic differences.

The Formant Bandwidth as a Measure of Vowel Intelligibility in Dysphonic Speech

The current paper examined the impact of dysphonia on the bandwidth of the first two formants of vowels, and the relationship between the formant bandwidth and vowel intelligibility. Speaker participants of the study were 10 adult females with healthy voice and 10 adult females with dysphonic voice. Eleven vowels in American English were recorded in /h/-vowel-/d/ format. The vowels were presented to 10 native speakers of American English with normal hearing, who were asked to select a vowel they heard from a list of /h/-vowel-/d/ words. The vowels were acoustically analyzed to measure the bandwidth of the first and second formants (B1 and B2). Separate Wilcoxon rank sum tests were conducted for each vowel for normal and dysphonic speech because the differences in B1 and B2 were found to not be normally distributed. Spearman correlation tests were conducted to evaluate the association between the difference in formant bandwidths and vowel intelligibility between the healthy and dysphonic speakers. B1 was significantly greater in dysphonic vowels for seven of the eleven vowels, and lesser for only one of the vowels. There was no statistically significant difference in B2 between the normal and dysphonic vowels, except for the vowel /i/. The difference in B1 between normal and dysphonic vowels strongly predicted the intelligibility difference. Dysphonia significantly affects B1, and the difference in B1 may serve as an acoustic marker for the intelligibility reduction in dysphonic vowels. This acoustic-perceptual relationship should be confirmed by a larger-scale study in the future.

Intelligibility Enhancement via Telepractice During COVID-19 Restrictions

Purpose Speech-language pathologists (SLPs) may be approached by multilingual speakers seeking to improve their intelligibility in English. Intelligibility is an essential element of spoken language proficiency and is especially important for multilingual university students given their need to express complex ideas in an additional language. Intelligibility Enhancement is an assessment and intervention approach that aims to improve the intelligibility of consonants, vowels, and prosody with multilingual speakers who are learning to speak English. This article describes the student-led delivery of Intelligibility Enhancement with multilingual clients in a university clinic using a telepractice model after restrictions were imposed due to the COVID-19 pandemic. Conclusions Telepractice offered an appropriate mode of service delivery that facilitated a high-quality, best practice, and continuous service to Intelligibility Enhancement clients while also permitting student SLPs' ongoing clinical education employing an increasingly utilized technology. Previous research demonstrated the effectiveness of the Intelligibility Enhancement Assessment and Intervention Protocols in increasing English intelligibility in multilingual university students. The modifications necessary to provide this intervention via telepractice in a student-led clinic not only offer a possible solution to supporting multilingual university students' English intelligibility during the COVID-19 pandemic but also will inform the understanding of SLPs providing similar interventions in the future.