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and realization of unaspirated affricates associated with Mandarin-speaking children with repaired cleft palate
International Journal of Pediatric Otorhinolaryngology 86 (2016) 150–155
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International Journal of Pediatric Otorhinolaryngology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / i j p o r l
Voice onset time of alveolar stop /t/ and realization of unaspirated affricates associated with Mandarin-speaking children with repaired cleft palate Chenghui Jiang a,b,*, Bradley McPherson b, Manwa L. Ng b a b
Stomatological College, Nanjing Medical University, Nanjing, China Division of Speech and Hearing Sciences, Faculty of Education, University of Hong Kong, Nanjing, China
A R T I C L E
I N F O
Article history: Received 25 January 2016 Received in revised form 28 March 2016 Accepted 28 March 2016 Available online 2 May 2016 Keywords: Affricate Chinese Cleft palate Mandarin Speech Voice onset time
A B S T R A C T
Purpose: To examine perceptually the realization of unaspirated affricates and voice onset time (VOT) features of /t/ in Mandarin-speaking children with repaired cleft palate, and to explore the difficulties associated with unaspirated affricate production from the perspective of the VOT of /t/. Method: Twenty-three children with repaired cleft palate and 22 age-matched typical native Mandarin speakers were recruited. Speakers with cleft palate were allocated into two groups based on expert perceptual judgment of nasality: one group with perceived normal resonance (PNR) (n = 14, average age = 9.3 years), and another group with perceived hypernasal resonance (PHR) (n = 9, average age = 10.3 years). Intervention: Stimuli were collected through a series of picture naming tasks, targeting the production of initial consonants /t/ and three unaspirated Mandarin affricates /ts, tʂ, tɕ/. The productions of each affricate were evaluated by two experienced speech therapists. The VOT of /t/ was measured using PRAAT speech analysis software. Result: The majority of unaspirated affricates were omitted and/or weakly realized by the group of PHR speakers, but not for the PNR group. A significantly smaller mean VOT value associated with /t/ was identified for the PHR group, as compared to the PNR group. A group difference for VOT value was not found between the PNR group and the typical control group. Conclusion: The voicing features of /t/ and omitted/weak realization of unaspirated affricates identified in the PHR group indicated that the deviant production of unaspirated affricates in the cleft palate group could be associated with the voicing characteristics of the alveolar stop /t/, and this merits further investigation. © 2016 Published by Elsevier Ireland Ltd.
1. Introduction Non-syndromic cleft lip and/or palate ranks as the third most common congenital deficiency in mainland China. About 20,000 babies are born with cleft palate every year [1]. Cleft palate +/− lip leads to multiple dysfunctions, including those related with feeding, speech, oral hygiene, occlusion and jaw development. The speech problems associated with cleft palate are of great concern for both the professionals working in the cleft team and the family members [2]. Both language-universal and language-specific error patterns have been identified from the speech produced by individuals with cleft palate [3]. However, little attention has been paid to the large
This research was supported in part by the Faculty of Education Research Fund University of Hong Kong. * Corresponding author at: Stomatological College, Nanjing Medical University, Nanjing, China. Tel.: +86 025 85031892. E-mail address: [email protected] (C. Jiang). http://dx.doi.org/10.1016/j.ijporl.2016.03.042 0165-5876/© 2016 Published by Elsevier Ireland Ltd.
population of Mandarin speakers with cleft palate. In one preliminary study of consonant error patterns in Mandarin-speaking children with repaired cleft palate it was reported that unaspirated affricates (/ts, tʂ, tɕ/) were more difficult to produce than aspirated affricates (/tsh, tʂh, tɕh/) [4]. The discrepant performance between aspirated and unaspirated affricates prompted for a more in-depth exploration of this issue for Mandarin speakers with cleft palate. Mandarin, also known as Putonghua, has the largest number of native speakers in the world (about 840 million speakers), and is the national spoken language in China [5,6]. In Putonghua phonology, there are three pairs of affricates distributed at different articulatory places – the alveolar, postalveolar (retroflex) and palatal regions (see Table 1). The two affricates in each pair can be distinguished from each other by the feature of aspiration [7]. Affricate is a manner of articulation characterized by a combination of stop and fricative articulatory components [8]. It can be further described as a period of complete occlusion of the vocal tract followed by a period of frication. Take the unaspirated affricate /ts/ as an example, it is produced with a period of complete occlusion at the
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Table 1 Affricates in Putonghua phonology. Place of articulation
Alveolar
Retroflex
Palatal
Phonemes
/ts,tsh/
/tʂ, tʂh/
/tɕ,tɕh/
alveolar ridge (as in /t/), and followed by a period of friction formulated at a similar articulatory place to /s/. The extent to which the plosive and fricative portions of affricates resemble their counterpart singleton plosive and fricative speech sounds has been extensively examined. Based on previous electropalatographic (EPG) studies of normal English, the fricative portion of an affricate was found to be associated with the same place of articulation as in singleton fricatives. Yet acoustic studies revealed a shorter frication period in affricates [8,9]. The plosive portion resembled the fricative in terms of place of articulation, as shown in EPG investigations. However, the placement of the plosive portion of /tʃ/ was significantly more posterior than the singleton /t/ and closer to the singleton fricative [10]. Similar findings were also reported with Chinese speakers of Cantonese [11]. These findings suggested that the realization of the affricates was strongly associated with how their components were produced in singletons (single plosives and fricatives), although most evidence was based on temporal and spatial perspectives. The same issue has also been investigated in children with speech disorders. Hardcastle, Gibbon, and Scobbie [12] made use of EPG to analyze the speech produced by ten English-speaking children with developmental speech disorders, who exhibited normal /t/ but deviated /ʃ/ and/or /tʃ/ productions. EPG results showed that the spatial features in singleton /ʃ/ (retracted or advanced) were present in the fricative portion of /tʃ/. The place of the plosive portion resembled the fricative portion. However, a case study of the affricate /tʃ/ produced by several children with atypical speech production showed different findings [13]. In one child, the lateralization of /ʃ/ was not demonstrated in the production of /tʃ/. Another child, who had a cleft of the soft palate attributed to Pierre Robinson sequence, exhibited variable /t/ production but consistent distortion of /ʃ/. His production of affricate /tʃ/ could be separated into two distinctive phonemes. It pointed out that the errors associated with the single fricative production were not present in the speakers’ affricate production. It appears that findings from normal speakers may not be totally applicable to speakers with speech disorder. Investigation of individuals with speech disorder (such as speakers with cleft palate) may provide complementary information to explain the controversial findings about the relationship between the single plosive/fricative and the affricate. Nevertheless, studies on speakers with or without speech disorder indicated that there is a potential relationship between singleton plosives and the realization of the affricate. It was also suggested that the exploration of singleton plosives, such as /t/, would be an effective approach to uncover misarticulations associated with affricate production in the cleft palate population. In order to investigate the plosive feature, the parameter of voice onset time (VOT), which is defined as the interval between the release of the oral occlusion for the plosive articulation and the onset of vocal fold vibration, is used to characterize the unaspirated plosive /t/ [14]. Wide-band spectrographic analysis shows the release point as an abrupt spectral change which signifies the transient noise burst. The first regularly spaced vertical striations show the onset of vocal fold vibration. If the vocal folds are set into vibration prior to the release of occlusion, as in voiced plosives, it results in a negative VOT value and is defined as a voicing lead, such as in Italian voiced stops. On the other hand, when the release of burst precedes the vocal fold vibration, the VOT value is positive and is defined as voicing lag [14,15]. Therefore, VOT can serve as a cue to distinguishing between
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voiced and voiceless, and between aspirated and unaspirated plosive cognates [14,15]. Some studies have been conducted to obtain normative VOT data on typical Chinese speakers, including for Cantonese [14] and Taiwan Mandarin [16] (both are dialects of Chinese). Previous studies also showed that VOT varies with place of articulation [17,18] as well as with different tones for tonal languages (e.g., Mandarin) [19]. The purpose of the present study was to examine the perceptual judgment of unaspirated affricates and the VOT features of the unaspirated alveolar plosive /t/ in Mandarin cleft speakers with repaired cleft palate, and to explore the articulatory difficulties associated with unaspirated affricates from the perspective of the VOT of /t/. Findings from the present study would not only add to our theoretical understanding of the relationship between a singleton plosive and affricates, but also contribute to our understanding of the articulation deviation in children with cleft palate and would provide directions for clinical intervention with this speech disordered population. 2. Method 2.1. Participants Data were excerpted from the data pool of a larger scale study (similar to Jiang et al [4]) in which speech produced by 23 Putonghua speakers with non-syndromic cleft palate was examined. The cleft participant group was comprised of 15 males and 8 females, with ages from 4.5 to 13 years (mean = 9.3 years, SD = 3.7 years). Of the cleft participants, ten had unilateral cleft lip and palate, nine had bilateral cleft lip and palate, and four had soft palate cleft only. The participants were recruited from two cleft palate centers in mainland China. All participants were native Putonghua speakers and received primary palatoplasty earlier than three years of age. None had a significant delay in academic performance as reported by their parents/grandparents. All the participants passed a pure-tone audiological screening at 25 dB HL for the octave frequencies 500 Hz to 2000 Hz, for the better hearing ear. A low-frequency probe tone of 226 Hz was used for screening tympanometry. Eleven participants had normal tympanograms bilaterally (type ‘A’ tympanograms with a clear peak maximum at or near 0 daPa) [20]. Three participants had normal tympanograms for only one ear (right or left). A flat tympanometric configuration was found for nine participants. An oral–facial examination was conducted to obtain information about the participants’ oral structures. All participants were divided into two groups based on results of perceptual resonance assessment (including the parameters of hypernasality, hyponasality and nasal emission), as judged by a panel of three speech therapists (Jiang et al [4]), following a wellestablished procedure [21]. One group had perceived normal resonance (PNR) (n = 14, mean = 9.25 years). The other group was assessed with perceived hypernasal resonance (PHR) (n = 9, mean = 10.27 years). The control group was comprised of 22 typical native Mandarinspeaking children (11 males and 11 females), aged from 4.5 to 13 years (mean = 8.6 years, SD = 2.7 years). They were recruited from a public primary school/kindergarten in the city of Nanjing, China. All participants were reported to have no history of speech, language, hearing, vision or intelligence problems by their teachers. All participants passed a pure-tone audiological screening at 25 dB HL at 500 Hz to 2000 Hz for the better hearing ear. 2.2. Ethical approval This project was approved by the Human Research Ethics Committee for Non-Clinical Faculties of the University of Hong Kong (Ref:
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EA030210). All parents provided written informed consent for their children’s participation in this research project. 2.3. Stimuli The speech stimuli were selected from Part One of the Putonghua Segmental Phonology Test (PSPT) [22] and the Deep Test for Cleft Palate Speakers in Putonghua (DTPSCP) [4]. Four target phonemes, /t/, /ʦ/, /ʈʂ/, /ʨ/, were examined in the present study. All target phonemes occurred in the syllable initial position. Each target affricate was produced four to six times, followed by different vowels (/ι/, /α/, etc.), with the exception of the palatal affricate. According to the morphophonemic rules in Putonghua, the palatal consonant (/ʨ/) can only be followed by two glides/semi-vowels: /ι/ and /υ/. The corpus provided a maximum of 18 possible words for each participant, including a few cases where the same word was repeated (see Appendix S1). Not all words were produced by all participants. Those words that could not be segmented with confidence because of background noise or overtalk were excluded from analysis. All data collection took place in a quiet room with a maximum background noise of 50 dB. A high-quality head-mounted miniature microphone (SHM 1900, Philips) (sensitivity: 30–15000 Hz) that was placed at a distance of approximately 10 cm from the participant’s mouth was used to obtain the audio recording. Audio signals were digitized at a sampling rate of 20 kHz and stored in a laptop computer (ThinkPad X201) for later analyses. The speech samples obtained from the participants’ picture naming task were audiorecorded through software Audacity 2.0.0 [23]. 3. Data analysis 3.1. Perceptual judgment of production of unaspirated affricates The target unaspirated affricate stimuli were perceived by two speech therapists (both had special training on the speech problems associated with individuals with cleft palate, and more than five years experience working in a cleft lip and palate center) and they made a judgment of the type of realization (accurate, weak, omission or other). The judgment of the speakers’ productions was confirmed through discussion among the panel.
Fig. 1. Percentage of different realizations for unaspirated affricates for two groups of cleft speakers; PHR = perceived hypernasal resonance, PNR = perceived normal resonance.
3.4. Reliability of acoustical analysis To obtain intra-rater reliability, 5% of the entire stimuli were transcribed a second time by the first rater (the first author) one month after the initial data collection. Similarly, for inter-rater reliability, 5% of the stimuli were transcribed by a research assistant who was trained in carrying out acoustic analysis. The Pearson productmoment correlation coefficients (r) associated with intra-rater and inter-rater reliability were 0.878 (p < 0.001) and 0.776 (p < 0.001) respectively, indicating that the VOT measurements provided by the researcher were both reliable and consistent. 4. Results 4.1. Perceptual judgment of unaspirated affricates
3.2. Acoustic analysis The excerpted tokens targeted on plosive /t/ were saved as .wav files and read into PRAAT (Version 5.4) speech analysis software. In total, 93 tokens for the typical speaker group, 71 tokens for the cleft speaker with PNR, and 61 for the cleft speakers with PHR, were saved. VOT was functionally defined as the time interval between the release of stop occlusion and the onset of the following vowel [8]. The measurements were obtained using both the analysis software waveform and spectrogram. Two cursors were positioned on the waveform; the first marker was used to indicate the release of the burst, and the second marker was placed at the first identifiable regular glottal pulse. VOT values (in milliseconds) were measured as the time interval between the two cursors [18].
The percentage of different realizations for unaspirated affricates was presented in Fig. 1. It showed that majority of the unaspirated affricates were realized as weak articulation (50.4%) and/ or omitted (20.9%) for the cleft speakers with PHR. For the group of cleft speakers with PNR, most of their unaspirated affricates were correctly produced (more than 80%), with no realization of weak or omission. The unaspirated affricates produced by typical speakers were all judged to be correct by two speech therapists. 4.2. Measurement of VOT Mean and standard deviation VOT values for each group of children are shown in Table 2. A main effect in the values of VOT was found for the three groups of speakers (X2 = 41.718, p < 0.001). Post
3.3. Statistical analysis For all statistical procedures, a significance level of p = 0.05 (twotailed) was used. Friedman ANOVA was used for non-parametric comparison of the three groups of speakers, with VOT values as the dependent variable. When Friedman ANOVA showed significant differences, a Wilcoxon signed-rank test was used for post hoc analyses, with a Bonferroni corrected p value for multiple comparisons (p < 0.016).
Table 2 Mean and standardized deviation (SD) of VOT (in ms) by group.
VOT (ms) SD
Typical speaker
Speaker with cleft palate PNR
PHR
10.5 11.9
11.9 20.4
−27.5 97.4
PNR = perceived normal resonance, PHR = perceived hypernasal resonance.
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Fig. 2. Boxplots for voice onset time (VOT; in ms) for three speaker groups; PNR = perceived normal resonance, PHR = perceived hypernasal resonance.
hoc tests revealed that the cleft speaker group with PHR (−27.5 ms) had a significantly lower VOT value than the cleft speaker group with PNR (11.9ms) (Z = −3.8, p < 0.001). The VOT value of the cleft speaker group with PHR (−27.5 ms) was also significantly lower than that for the typical speaker group (10.5 ms) (Z = −5.0, p < 0.001). However, there was no significant difference in VOT value between the typical speaker group (10.5 ms) and the cleft speaker group with PNR (11.9 ms). As shown in Fig. 2, the mean VOT value between the typical speaker group and the cleft speaker with PNR group was not significantly different. However, the variability of the cleft group with PNR was much larger than for the typical speaker group. The majority of the VOT values for both two groups were positive, while for the cleft speakers with PHR most of the VOT values were below zero. 5. Discussion As reported previously [4], unaspirated consonants including both unaspirated plosives and affricates were produced with lower accuracy than their aspirated counterparts. The perceptual judgment of unaspirated affricates found in the present study well supports this finding, as much less accurate productions were achieved in the group of cleft speakers with PHR than the PNR group. Furthermore, this study also offered more information regarding the types of realization of those unaspirated affricates. It was reported that a large proportion of unaspirated affricates (around 80%) was weakly produced or omitted in the PHR group. Interestingly, the second aspect of the present study, regarding the VOT features of the unaspirated alveolar plosive /t/, may facilitate our understanding on the misarticulation of the unaspirated affricates identified in the cleft speakers with PHR. 5.1. Voicing of unaspirated voiceless stop /t/ In Putonghua phonology, all oral consonants are voiceless. However, in the present study, for the group of cleft speakers with PHR, significantly lower and negative VOT values were found for
the unaspirated plosive /t/, as compared with both the group of speakers with PNR and typical speakers. This implied a voicing lead/ voiced realization for the target unaspirated voiceless stop /t/. It was important to explore why this happened in this group of participants. The literature on the production of voiced speech sounds provide some possible explanations. Firstly, during the articulation of voiced sounds, the vocal-fold vibration is created by a pressure differential across the glottis, which ensures enough airflow for a transfer of energy to the vocal fold tissues. For typical speech production, the threshold value of the pressure differential is estimated at about 2–3 cm H2O [24]. During the production of oral consonants, the constriction between articulators in the upper vocal tract increases the intraoral/supraglottal pressure (Pio). Consequently, this leads to a decrease in the value of the transglottal pressure difference (Ptrans). Once the Ptrans is below a threshold value, voicing stops. However, speakers can use certain compensatory actions to slow the rate of Pio increase, in order to maintain the condition of voicing [25,26], such as moving the larynx to expand the supraglottal volume [27], or by incomplete closure of the velopharyngeal port [28]. The latter is commonly identified in speakers who have undergone primary closure of cleft palate, and in whom velopharyngeal competence cannot be achieved [2]. Even those with sufficient velopharyngeal function may still maintain old production habits, with air leakage to the nasal cavity during oral articulation [2]. For the group of cleft speakers with PHR, perceptual judgment of hypernasality indicated a strong possibility of velopharyngeal inadequacy, which would passively facilitate prolongation of voicing. Secondly, a glottal reinforcement explanation is also plausible when a voiceless stop is produced with a negative VOT [29]. The term glottal reinforcement refers to the addition of a glottal gesture along with a supralaryngeal gesture [30]. Tollfree [31] pointed out that glottal reinforcement of voiceless stops is quite common, particularly in the syllable-final non-pre-vocalic position in Australian English speakers. It is also frequently identified in both English and Swedish speakers with cleft palate, as a typical cleft-type speech characteristic [32,33].
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5.2. Weak articulation and/or omission of unaspirated affricates As both a negatively lower VOT value for unaspirated /t/ and weak and/or omission for the unaspirated affricates were found in the group of cleft speakers with PHR, it is reasonable to suspect that the voiced /t/ production may contribute to the falsely produced unaspirated affricates. This hypothesis is in line with the phenomenon that voiced sibilant affricates tend to be absent despite the presence of their voiceless counterparts in typical speakers in many language families [34]. In other languages, voiced affricates have a limited distribution or have marginal phonological status [34]. Further examination of such phonological processes showed that the voiced affricates are less frequently created and more likely to be deaffricated, as compared with their voiceless counterparts [34]. The manner of affricate production is considered to be created from other sounds, mainly stops [35], in order to establish a contrast in the speaker’s phonological inventory. Guion [36] reported affrication was more likely to happen in voiceless velar stops, while voiced velar stops changed to glides or fricatives. Telfer [37] claimed that in the Puglia, Salento, and Lucania dialects of Italian, when a voiceless velar stop became an affricate, the voiced /g/ was deleted. All those studies suggest that voiced and voiceless stops do not behave in a parallel manner in the process of affrication. Other evidence indicates that sibilant voiced affricates are unstable and tended to convert to voiced fricatives (e.g., in Shanghai Chinese [38];). As described in the previous section, once a constriction between two articulators is achieved in the oral cavity, it is difficult to maintain voicing, unless the speaker adopts compensatory maneuvers or obtains greater aerodynamic control. Those production requirements for voiced consonants make it comparatively difficult to form voiced affricates. This could provide an explanation for the finding that in the group of cleft speakers with PHR, once the /t/ was voiced, it was difficult to produce voiced affricates, which resulted in omission or weak articulation of the target unaspirated affricates. Omission/weak production for unaspirated affricates associated with speakers with repaired cleft palate in the PHR group can also be explained from the perspective of competing demands for maintaining both voicing and the fricative noise of the affricate. Only a restricted aerodynamic range (around 3 to 5.6 cm H2O) permits the achievement of both phonation and frication together [39,40]. Therefore, specific articulatory adjustments are needed to increase airflow and facilitate frication. This may cause difficulty for the cleft speakers and may result in omission the whole affricate or weak articulation. Another possible alternative is to use the approximant as a substitution for the fricative, to maintain the aerodynamic requirements for vocal-fold vibration. Further investigation is needed to explore this issue.
5.3. Theoretical contribution and clinical implications Findings from the present study suggest that problems associated with the singleton plosive /t/ may influence realizations of unaspirated affricates that are in cleft speakers’ phonological inventories. This supports previous studies in typical speakers that indicate the plosive and fricative portions of affricates resemble their counterpart singleton plosives and fricatives [8–11]. Furthermore, the results from this study also indicate that the plosive portion may be an anchor for realization of the affricate. Several theories have been proposed to describe the representation of affricates (see Reference [41] for a summary), among which the stop analysis approach [42] has a greater evidence base. One strong example is that affricates and stops are in complementary distribution in terms of place of articulation in many languages. For overlaps that occur in the dental/alveolar area, the feature [+strident] could well distinguish affricates from homorganic stops without a distinct class for
affricates [42]. Therefore, it is concluded that affricates are represented phonologically as stops. Although no definitive conclusion could be drawn from this study regarding the phonological representation of affricates, it does support the critical contribution of the plosive portion in affricate production. Findings arising from the present study not only contribute to our understanding of the phonology of affricates, but also have potential clinical implications. The manner of affricate production constitutes more than one third of the consonant inventory of Mandarin phonology. Misarticulation of affricates would lead to significant deterioration of speaker intelligibility. It is suggested that during the process of initial assessment, when the speech therapist encounters cleft palate patients with consistent unaspirated affricate articulation problems, special attention should be paid to the production of the speakers’ plosive /t/. In cases where the voiceless plosive /t/ is voiced and produced/with glottal reinforcement, it is necessary to carefully examine the velopharyngeal function of the speaker, as both physical velopharyngeal adequacy and mislearning of velopharyngeal function could lead to this error pattern. For practical reasons, only perceptual resonance assessment was conducted during the initial data collection in the present study. Through a panel of experienced speech therapists, the presence or absence of perceived hypernasality in participant speech was noted. However, no detailed information regarding velopharyngeal function was obtained. It is suggested that instrumental examination, such as nasendoscopy or nasometry, should be used to explore speaker status for velopharyngeal closure [43]. Once physical velopharyngeal incompetence is excluded, speech intervention should be delivered to help the patient to establish the correct voicing features of the plosive /t/. This may be the foundation for him/her to realize the correct manner of other unaspirated affricates. This approach needs to be tested in future evidence-based clinical trials.
6. Conclusion The current study aimed to examine the perceptual judgment of unaspirated affricates and the VOT feature of the unaspirated alveolar plosive /t/ in Mandarin cleft speakers with repaired cleft palate, and to explore the production difficulties of unaspirated affricates from the perspective of the VOT of /t/ in this population. Compared with typical speakers, the cleft speakers with PNR showed no significant difference in mean VOT values. However, those cleft speakers who presented with PHR had significantly lower VOT values than the typical speaker group. The negative mean VOT value indicated those cleft speakers used voiced plosives to substitute for the unaspirated voiceless plosive, which could contribute to the omission/weak articulation of the unaspirated affricates identified in their speech. Multiple reasons for the voicing change of plosives and their possible influence on the omission/weak articulation of the unaspirated affricates were discussed, and the potential clinical implications of this finding addressed.
Declaration The authors reported no conflict of interest.
Acknowledgments This research was supported in part by the Faculty of Education Research Fund, University of Hong Kong. We are grateful to Mr. Dustin Wang for his help with re-analyzing part of the speech data. We also greatly appreciate the support provided by Jiangsu Stomatological Hospital and Xuzhou First Peoples Hospital during the
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data collection process. Thanks are extended to the children and their families for their participation.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ijporl.2016.03.042.
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International Journal of Pediatric Otorhinolaryngology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / i j p o r l
Voice onset time of alveolar stop /t/ and realization of unaspirated affricates associated with Mandarin-speaking children with repaired cleft palate Chenghui Jiang a,b,*, Bradley McPherson b, Manwa L. Ng b a b
Stomatological College, Nanjing Medical University, Nanjing, China Division of Speech and Hearing Sciences, Faculty of Education, University of Hong Kong, Nanjing, China
A R T I C L E
I N F O
Article history: Received 25 January 2016 Received in revised form 28 March 2016 Accepted 28 March 2016 Available online 2 May 2016 Keywords: Affricate Chinese Cleft palate Mandarin Speech Voice onset time
A B S T R A C T
Purpose: To examine perceptually the realization of unaspirated affricates and voice onset time (VOT) features of /t/ in Mandarin-speaking children with repaired cleft palate, and to explore the difficulties associated with unaspirated affricate production from the perspective of the VOT of /t/. Method: Twenty-three children with repaired cleft palate and 22 age-matched typical native Mandarin speakers were recruited. Speakers with cleft palate were allocated into two groups based on expert perceptual judgment of nasality: one group with perceived normal resonance (PNR) (n = 14, average age = 9.3 years), and another group with perceived hypernasal resonance (PHR) (n = 9, average age = 10.3 years). Intervention: Stimuli were collected through a series of picture naming tasks, targeting the production of initial consonants /t/ and three unaspirated Mandarin affricates /ts, tʂ, tɕ/. The productions of each affricate were evaluated by two experienced speech therapists. The VOT of /t/ was measured using PRAAT speech analysis software. Result: The majority of unaspirated affricates were omitted and/or weakly realized by the group of PHR speakers, but not for the PNR group. A significantly smaller mean VOT value associated with /t/ was identified for the PHR group, as compared to the PNR group. A group difference for VOT value was not found between the PNR group and the typical control group. Conclusion: The voicing features of /t/ and omitted/weak realization of unaspirated affricates identified in the PHR group indicated that the deviant production of unaspirated affricates in the cleft palate group could be associated with the voicing characteristics of the alveolar stop /t/, and this merits further investigation. © 2016 Published by Elsevier Ireland Ltd.
1. Introduction Non-syndromic cleft lip and/or palate ranks as the third most common congenital deficiency in mainland China. About 20,000 babies are born with cleft palate every year [1]. Cleft palate +/− lip leads to multiple dysfunctions, including those related with feeding, speech, oral hygiene, occlusion and jaw development. The speech problems associated with cleft palate are of great concern for both the professionals working in the cleft team and the family members [2]. Both language-universal and language-specific error patterns have been identified from the speech produced by individuals with cleft palate [3]. However, little attention has been paid to the large
This research was supported in part by the Faculty of Education Research Fund University of Hong Kong. * Corresponding author at: Stomatological College, Nanjing Medical University, Nanjing, China. Tel.: +86 025 85031892. E-mail address: [email protected] (C. Jiang). http://dx.doi.org/10.1016/j.ijporl.2016.03.042 0165-5876/© 2016 Published by Elsevier Ireland Ltd.
population of Mandarin speakers with cleft palate. In one preliminary study of consonant error patterns in Mandarin-speaking children with repaired cleft palate it was reported that unaspirated affricates (/ts, tʂ, tɕ/) were more difficult to produce than aspirated affricates (/tsh, tʂh, tɕh/) [4]. The discrepant performance between aspirated and unaspirated affricates prompted for a more in-depth exploration of this issue for Mandarin speakers with cleft palate. Mandarin, also known as Putonghua, has the largest number of native speakers in the world (about 840 million speakers), and is the national spoken language in China [5,6]. In Putonghua phonology, there are three pairs of affricates distributed at different articulatory places – the alveolar, postalveolar (retroflex) and palatal regions (see Table 1). The two affricates in each pair can be distinguished from each other by the feature of aspiration [7]. Affricate is a manner of articulation characterized by a combination of stop and fricative articulatory components [8]. It can be further described as a period of complete occlusion of the vocal tract followed by a period of frication. Take the unaspirated affricate /ts/ as an example, it is produced with a period of complete occlusion at the
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Table 1 Affricates in Putonghua phonology. Place of articulation
Alveolar
Retroflex
Palatal
Phonemes
/ts,tsh/
/tʂ, tʂh/
/tɕ,tɕh/
alveolar ridge (as in /t/), and followed by a period of friction formulated at a similar articulatory place to /s/. The extent to which the plosive and fricative portions of affricates resemble their counterpart singleton plosive and fricative speech sounds has been extensively examined. Based on previous electropalatographic (EPG) studies of normal English, the fricative portion of an affricate was found to be associated with the same place of articulation as in singleton fricatives. Yet acoustic studies revealed a shorter frication period in affricates [8,9]. The plosive portion resembled the fricative in terms of place of articulation, as shown in EPG investigations. However, the placement of the plosive portion of /tʃ/ was significantly more posterior than the singleton /t/ and closer to the singleton fricative [10]. Similar findings were also reported with Chinese speakers of Cantonese [11]. These findings suggested that the realization of the affricates was strongly associated with how their components were produced in singletons (single plosives and fricatives), although most evidence was based on temporal and spatial perspectives. The same issue has also been investigated in children with speech disorders. Hardcastle, Gibbon, and Scobbie [12] made use of EPG to analyze the speech produced by ten English-speaking children with developmental speech disorders, who exhibited normal /t/ but deviated /ʃ/ and/or /tʃ/ productions. EPG results showed that the spatial features in singleton /ʃ/ (retracted or advanced) were present in the fricative portion of /tʃ/. The place of the plosive portion resembled the fricative portion. However, a case study of the affricate /tʃ/ produced by several children with atypical speech production showed different findings [13]. In one child, the lateralization of /ʃ/ was not demonstrated in the production of /tʃ/. Another child, who had a cleft of the soft palate attributed to Pierre Robinson sequence, exhibited variable /t/ production but consistent distortion of /ʃ/. His production of affricate /tʃ/ could be separated into two distinctive phonemes. It pointed out that the errors associated with the single fricative production were not present in the speakers’ affricate production. It appears that findings from normal speakers may not be totally applicable to speakers with speech disorder. Investigation of individuals with speech disorder (such as speakers with cleft palate) may provide complementary information to explain the controversial findings about the relationship between the single plosive/fricative and the affricate. Nevertheless, studies on speakers with or without speech disorder indicated that there is a potential relationship between singleton plosives and the realization of the affricate. It was also suggested that the exploration of singleton plosives, such as /t/, would be an effective approach to uncover misarticulations associated with affricate production in the cleft palate population. In order to investigate the plosive feature, the parameter of voice onset time (VOT), which is defined as the interval between the release of the oral occlusion for the plosive articulation and the onset of vocal fold vibration, is used to characterize the unaspirated plosive /t/ [14]. Wide-band spectrographic analysis shows the release point as an abrupt spectral change which signifies the transient noise burst. The first regularly spaced vertical striations show the onset of vocal fold vibration. If the vocal folds are set into vibration prior to the release of occlusion, as in voiced plosives, it results in a negative VOT value and is defined as a voicing lead, such as in Italian voiced stops. On the other hand, when the release of burst precedes the vocal fold vibration, the VOT value is positive and is defined as voicing lag [14,15]. Therefore, VOT can serve as a cue to distinguishing between
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voiced and voiceless, and between aspirated and unaspirated plosive cognates [14,15]. Some studies have been conducted to obtain normative VOT data on typical Chinese speakers, including for Cantonese [14] and Taiwan Mandarin [16] (both are dialects of Chinese). Previous studies also showed that VOT varies with place of articulation [17,18] as well as with different tones for tonal languages (e.g., Mandarin) [19]. The purpose of the present study was to examine the perceptual judgment of unaspirated affricates and the VOT features of the unaspirated alveolar plosive /t/ in Mandarin cleft speakers with repaired cleft palate, and to explore the articulatory difficulties associated with unaspirated affricates from the perspective of the VOT of /t/. Findings from the present study would not only add to our theoretical understanding of the relationship between a singleton plosive and affricates, but also contribute to our understanding of the articulation deviation in children with cleft palate and would provide directions for clinical intervention with this speech disordered population. 2. Method 2.1. Participants Data were excerpted from the data pool of a larger scale study (similar to Jiang et al [4]) in which speech produced by 23 Putonghua speakers with non-syndromic cleft palate was examined. The cleft participant group was comprised of 15 males and 8 females, with ages from 4.5 to 13 years (mean = 9.3 years, SD = 3.7 years). Of the cleft participants, ten had unilateral cleft lip and palate, nine had bilateral cleft lip and palate, and four had soft palate cleft only. The participants were recruited from two cleft palate centers in mainland China. All participants were native Putonghua speakers and received primary palatoplasty earlier than three years of age. None had a significant delay in academic performance as reported by their parents/grandparents. All the participants passed a pure-tone audiological screening at 25 dB HL for the octave frequencies 500 Hz to 2000 Hz, for the better hearing ear. A low-frequency probe tone of 226 Hz was used for screening tympanometry. Eleven participants had normal tympanograms bilaterally (type ‘A’ tympanograms with a clear peak maximum at or near 0 daPa) [20]. Three participants had normal tympanograms for only one ear (right or left). A flat tympanometric configuration was found for nine participants. An oral–facial examination was conducted to obtain information about the participants’ oral structures. All participants were divided into two groups based on results of perceptual resonance assessment (including the parameters of hypernasality, hyponasality and nasal emission), as judged by a panel of three speech therapists (Jiang et al [4]), following a wellestablished procedure [21]. One group had perceived normal resonance (PNR) (n = 14, mean = 9.25 years). The other group was assessed with perceived hypernasal resonance (PHR) (n = 9, mean = 10.27 years). The control group was comprised of 22 typical native Mandarinspeaking children (11 males and 11 females), aged from 4.5 to 13 years (mean = 8.6 years, SD = 2.7 years). They were recruited from a public primary school/kindergarten in the city of Nanjing, China. All participants were reported to have no history of speech, language, hearing, vision or intelligence problems by their teachers. All participants passed a pure-tone audiological screening at 25 dB HL at 500 Hz to 2000 Hz for the better hearing ear. 2.2. Ethical approval This project was approved by the Human Research Ethics Committee for Non-Clinical Faculties of the University of Hong Kong (Ref:
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EA030210). All parents provided written informed consent for their children’s participation in this research project. 2.3. Stimuli The speech stimuli were selected from Part One of the Putonghua Segmental Phonology Test (PSPT) [22] and the Deep Test for Cleft Palate Speakers in Putonghua (DTPSCP) [4]. Four target phonemes, /t/, /ʦ/, /ʈʂ/, /ʨ/, were examined in the present study. All target phonemes occurred in the syllable initial position. Each target affricate was produced four to six times, followed by different vowels (/ι/, /α/, etc.), with the exception of the palatal affricate. According to the morphophonemic rules in Putonghua, the palatal consonant (/ʨ/) can only be followed by two glides/semi-vowels: /ι/ and /υ/. The corpus provided a maximum of 18 possible words for each participant, including a few cases where the same word was repeated (see Appendix S1). Not all words were produced by all participants. Those words that could not be segmented with confidence because of background noise or overtalk were excluded from analysis. All data collection took place in a quiet room with a maximum background noise of 50 dB. A high-quality head-mounted miniature microphone (SHM 1900, Philips) (sensitivity: 30–15000 Hz) that was placed at a distance of approximately 10 cm from the participant’s mouth was used to obtain the audio recording. Audio signals were digitized at a sampling rate of 20 kHz and stored in a laptop computer (ThinkPad X201) for later analyses. The speech samples obtained from the participants’ picture naming task were audiorecorded through software Audacity 2.0.0 [23]. 3. Data analysis 3.1. Perceptual judgment of production of unaspirated affricates The target unaspirated affricate stimuli were perceived by two speech therapists (both had special training on the speech problems associated with individuals with cleft palate, and more than five years experience working in a cleft lip and palate center) and they made a judgment of the type of realization (accurate, weak, omission or other). The judgment of the speakers’ productions was confirmed through discussion among the panel.
Fig. 1. Percentage of different realizations for unaspirated affricates for two groups of cleft speakers; PHR = perceived hypernasal resonance, PNR = perceived normal resonance.
3.4. Reliability of acoustical analysis To obtain intra-rater reliability, 5% of the entire stimuli were transcribed a second time by the first rater (the first author) one month after the initial data collection. Similarly, for inter-rater reliability, 5% of the stimuli were transcribed by a research assistant who was trained in carrying out acoustic analysis. The Pearson productmoment correlation coefficients (r) associated with intra-rater and inter-rater reliability were 0.878 (p < 0.001) and 0.776 (p < 0.001) respectively, indicating that the VOT measurements provided by the researcher were both reliable and consistent. 4. Results 4.1. Perceptual judgment of unaspirated affricates
3.2. Acoustic analysis The excerpted tokens targeted on plosive /t/ were saved as .wav files and read into PRAAT (Version 5.4) speech analysis software. In total, 93 tokens for the typical speaker group, 71 tokens for the cleft speaker with PNR, and 61 for the cleft speakers with PHR, were saved. VOT was functionally defined as the time interval between the release of stop occlusion and the onset of the following vowel [8]. The measurements were obtained using both the analysis software waveform and spectrogram. Two cursors were positioned on the waveform; the first marker was used to indicate the release of the burst, and the second marker was placed at the first identifiable regular glottal pulse. VOT values (in milliseconds) were measured as the time interval between the two cursors [18].
The percentage of different realizations for unaspirated affricates was presented in Fig. 1. It showed that majority of the unaspirated affricates were realized as weak articulation (50.4%) and/ or omitted (20.9%) for the cleft speakers with PHR. For the group of cleft speakers with PNR, most of their unaspirated affricates were correctly produced (more than 80%), with no realization of weak or omission. The unaspirated affricates produced by typical speakers were all judged to be correct by two speech therapists. 4.2. Measurement of VOT Mean and standard deviation VOT values for each group of children are shown in Table 2. A main effect in the values of VOT was found for the three groups of speakers (X2 = 41.718, p < 0.001). Post
3.3. Statistical analysis For all statistical procedures, a significance level of p = 0.05 (twotailed) was used. Friedman ANOVA was used for non-parametric comparison of the three groups of speakers, with VOT values as the dependent variable. When Friedman ANOVA showed significant differences, a Wilcoxon signed-rank test was used for post hoc analyses, with a Bonferroni corrected p value for multiple comparisons (p < 0.016).
Table 2 Mean and standardized deviation (SD) of VOT (in ms) by group.
VOT (ms) SD
Typical speaker
Speaker with cleft palate PNR
PHR
10.5 11.9
11.9 20.4
−27.5 97.4
PNR = perceived normal resonance, PHR = perceived hypernasal resonance.
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Fig. 2. Boxplots for voice onset time (VOT; in ms) for three speaker groups; PNR = perceived normal resonance, PHR = perceived hypernasal resonance.
hoc tests revealed that the cleft speaker group with PHR (−27.5 ms) had a significantly lower VOT value than the cleft speaker group with PNR (11.9ms) (Z = −3.8, p < 0.001). The VOT value of the cleft speaker group with PHR (−27.5 ms) was also significantly lower than that for the typical speaker group (10.5 ms) (Z = −5.0, p < 0.001). However, there was no significant difference in VOT value between the typical speaker group (10.5 ms) and the cleft speaker group with PNR (11.9 ms). As shown in Fig. 2, the mean VOT value between the typical speaker group and the cleft speaker with PNR group was not significantly different. However, the variability of the cleft group with PNR was much larger than for the typical speaker group. The majority of the VOT values for both two groups were positive, while for the cleft speakers with PHR most of the VOT values were below zero. 5. Discussion As reported previously [4], unaspirated consonants including both unaspirated plosives and affricates were produced with lower accuracy than their aspirated counterparts. The perceptual judgment of unaspirated affricates found in the present study well supports this finding, as much less accurate productions were achieved in the group of cleft speakers with PHR than the PNR group. Furthermore, this study also offered more information regarding the types of realization of those unaspirated affricates. It was reported that a large proportion of unaspirated affricates (around 80%) was weakly produced or omitted in the PHR group. Interestingly, the second aspect of the present study, regarding the VOT features of the unaspirated alveolar plosive /t/, may facilitate our understanding on the misarticulation of the unaspirated affricates identified in the cleft speakers with PHR. 5.1. Voicing of unaspirated voiceless stop /t/ In Putonghua phonology, all oral consonants are voiceless. However, in the present study, for the group of cleft speakers with PHR, significantly lower and negative VOT values were found for
the unaspirated plosive /t/, as compared with both the group of speakers with PNR and typical speakers. This implied a voicing lead/ voiced realization for the target unaspirated voiceless stop /t/. It was important to explore why this happened in this group of participants. The literature on the production of voiced speech sounds provide some possible explanations. Firstly, during the articulation of voiced sounds, the vocal-fold vibration is created by a pressure differential across the glottis, which ensures enough airflow for a transfer of energy to the vocal fold tissues. For typical speech production, the threshold value of the pressure differential is estimated at about 2–3 cm H2O [24]. During the production of oral consonants, the constriction between articulators in the upper vocal tract increases the intraoral/supraglottal pressure (Pio). Consequently, this leads to a decrease in the value of the transglottal pressure difference (Ptrans). Once the Ptrans is below a threshold value, voicing stops. However, speakers can use certain compensatory actions to slow the rate of Pio increase, in order to maintain the condition of voicing [25,26], such as moving the larynx to expand the supraglottal volume [27], or by incomplete closure of the velopharyngeal port [28]. The latter is commonly identified in speakers who have undergone primary closure of cleft palate, and in whom velopharyngeal competence cannot be achieved [2]. Even those with sufficient velopharyngeal function may still maintain old production habits, with air leakage to the nasal cavity during oral articulation [2]. For the group of cleft speakers with PHR, perceptual judgment of hypernasality indicated a strong possibility of velopharyngeal inadequacy, which would passively facilitate prolongation of voicing. Secondly, a glottal reinforcement explanation is also plausible when a voiceless stop is produced with a negative VOT [29]. The term glottal reinforcement refers to the addition of a glottal gesture along with a supralaryngeal gesture [30]. Tollfree [31] pointed out that glottal reinforcement of voiceless stops is quite common, particularly in the syllable-final non-pre-vocalic position in Australian English speakers. It is also frequently identified in both English and Swedish speakers with cleft palate, as a typical cleft-type speech characteristic [32,33].
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5.2. Weak articulation and/or omission of unaspirated affricates As both a negatively lower VOT value for unaspirated /t/ and weak and/or omission for the unaspirated affricates were found in the group of cleft speakers with PHR, it is reasonable to suspect that the voiced /t/ production may contribute to the falsely produced unaspirated affricates. This hypothesis is in line with the phenomenon that voiced sibilant affricates tend to be absent despite the presence of their voiceless counterparts in typical speakers in many language families [34]. In other languages, voiced affricates have a limited distribution or have marginal phonological status [34]. Further examination of such phonological processes showed that the voiced affricates are less frequently created and more likely to be deaffricated, as compared with their voiceless counterparts [34]. The manner of affricate production is considered to be created from other sounds, mainly stops [35], in order to establish a contrast in the speaker’s phonological inventory. Guion [36] reported affrication was more likely to happen in voiceless velar stops, while voiced velar stops changed to glides or fricatives. Telfer [37] claimed that in the Puglia, Salento, and Lucania dialects of Italian, when a voiceless velar stop became an affricate, the voiced /g/ was deleted. All those studies suggest that voiced and voiceless stops do not behave in a parallel manner in the process of affrication. Other evidence indicates that sibilant voiced affricates are unstable and tended to convert to voiced fricatives (e.g., in Shanghai Chinese [38];). As described in the previous section, once a constriction between two articulators is achieved in the oral cavity, it is difficult to maintain voicing, unless the speaker adopts compensatory maneuvers or obtains greater aerodynamic control. Those production requirements for voiced consonants make it comparatively difficult to form voiced affricates. This could provide an explanation for the finding that in the group of cleft speakers with PHR, once the /t/ was voiced, it was difficult to produce voiced affricates, which resulted in omission or weak articulation of the target unaspirated affricates. Omission/weak production for unaspirated affricates associated with speakers with repaired cleft palate in the PHR group can also be explained from the perspective of competing demands for maintaining both voicing and the fricative noise of the affricate. Only a restricted aerodynamic range (around 3 to 5.6 cm H2O) permits the achievement of both phonation and frication together [39,40]. Therefore, specific articulatory adjustments are needed to increase airflow and facilitate frication. This may cause difficulty for the cleft speakers and may result in omission the whole affricate or weak articulation. Another possible alternative is to use the approximant as a substitution for the fricative, to maintain the aerodynamic requirements for vocal-fold vibration. Further investigation is needed to explore this issue.
5.3. Theoretical contribution and clinical implications Findings from the present study suggest that problems associated with the singleton plosive /t/ may influence realizations of unaspirated affricates that are in cleft speakers’ phonological inventories. This supports previous studies in typical speakers that indicate the plosive and fricative portions of affricates resemble their counterpart singleton plosives and fricatives [8–11]. Furthermore, the results from this study also indicate that the plosive portion may be an anchor for realization of the affricate. Several theories have been proposed to describe the representation of affricates (see Reference [41] for a summary), among which the stop analysis approach [42] has a greater evidence base. One strong example is that affricates and stops are in complementary distribution in terms of place of articulation in many languages. For overlaps that occur in the dental/alveolar area, the feature [+strident] could well distinguish affricates from homorganic stops without a distinct class for
affricates [42]. Therefore, it is concluded that affricates are represented phonologically as stops. Although no definitive conclusion could be drawn from this study regarding the phonological representation of affricates, it does support the critical contribution of the plosive portion in affricate production. Findings arising from the present study not only contribute to our understanding of the phonology of affricates, but also have potential clinical implications. The manner of affricate production constitutes more than one third of the consonant inventory of Mandarin phonology. Misarticulation of affricates would lead to significant deterioration of speaker intelligibility. It is suggested that during the process of initial assessment, when the speech therapist encounters cleft palate patients with consistent unaspirated affricate articulation problems, special attention should be paid to the production of the speakers’ plosive /t/. In cases where the voiceless plosive /t/ is voiced and produced/with glottal reinforcement, it is necessary to carefully examine the velopharyngeal function of the speaker, as both physical velopharyngeal adequacy and mislearning of velopharyngeal function could lead to this error pattern. For practical reasons, only perceptual resonance assessment was conducted during the initial data collection in the present study. Through a panel of experienced speech therapists, the presence or absence of perceived hypernasality in participant speech was noted. However, no detailed information regarding velopharyngeal function was obtained. It is suggested that instrumental examination, such as nasendoscopy or nasometry, should be used to explore speaker status for velopharyngeal closure [43]. Once physical velopharyngeal incompetence is excluded, speech intervention should be delivered to help the patient to establish the correct voicing features of the plosive /t/. This may be the foundation for him/her to realize the correct manner of other unaspirated affricates. This approach needs to be tested in future evidence-based clinical trials.
6. Conclusion The current study aimed to examine the perceptual judgment of unaspirated affricates and the VOT feature of the unaspirated alveolar plosive /t/ in Mandarin cleft speakers with repaired cleft palate, and to explore the production difficulties of unaspirated affricates from the perspective of the VOT of /t/ in this population. Compared with typical speakers, the cleft speakers with PNR showed no significant difference in mean VOT values. However, those cleft speakers who presented with PHR had significantly lower VOT values than the typical speaker group. The negative mean VOT value indicated those cleft speakers used voiced plosives to substitute for the unaspirated voiceless plosive, which could contribute to the omission/weak articulation of the unaspirated affricates identified in their speech. Multiple reasons for the voicing change of plosives and their possible influence on the omission/weak articulation of the unaspirated affricates were discussed, and the potential clinical implications of this finding addressed.
Declaration The authors reported no conflict of interest.
Acknowledgments This research was supported in part by the Faculty of Education Research Fund, University of Hong Kong. We are grateful to Mr. Dustin Wang for his help with re-analyzing part of the speech data. We also greatly appreciate the support provided by Jiangsu Stomatological Hospital and Xuzhou First Peoples Hospital during the
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data collection process. Thanks are extended to the children and their families for their participation.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ijporl.2016.03.042.
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