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Phonological contrast and neutralization by children with cochlear implants
International Congress Series 1273 (2004) 328 – 331
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Phonological contrast and neutralization by children with cochlear implants Steven B. Chin*, Joseph E. Krug Department of Otolaryngology, Indiana University School of Medicine, 699 West Dr., RR044, Indianapolis, IN 46202-5119, USA
Abstract. Objective: To determine the degree to which pediatric users of cochlear implants (CIs) implement neutralization of the /t/ vs. /d/ contrast under different pragmatic conditions. Study design: Children who used cochlear implants and both children and adults with normal hearing produced minimal pairs contrasting lexical /t/ and /d/ in three conditions that gradually increased the need to differentiate members of the pairs, ranging from neutralization through implicit contrast to explicit contrast. Duration of the preceding vowel, the stop occlusion, and voice onset time following release were measured. Results: Adults exhibited small differences between /t/ and /d/ in the neutralization condition; differences increased through the remaining conditions. For the children, differences between /t/ and /d/ in the neutralization condition were relatively large, and differences between /t/ and /d/ did not increase monotonically through the conditions. Conclusion: Adults with normal hearing implement contrast and neutralization depending on pragmatic context. Children with either normal hearing or cochlear implants exhibit less differentiation, tending to maintain contrastiveness regardless of pragmatic condition. D 2004 Elsevier B.V. All rights reserved.
Keywords: Cochlear implantation; Language acquisition; Phonological contrast; Phonological neutralization
1. Introduction Contrast is the property of language whereby sound segments can differentiate the meanings of lexical items. Minimal pairs of words, such as ten vs. den and bet vs. bed indicate a contrast between /t/ and /d/ in English, because the differences in meaning derive solely from the fact that one word has /t/ where the other has /d/ (all other phonetic material, -en or be-, being identical). Another property is that contrasts can be obliterated, * Corresponding author. Tel.: +1 317 274 4981; fax: +1 317 274 4949. E-mail address: [email protected] (S.B. Chin). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.08.004
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or neutralized, in specific phonetic environments. As the cited minimal pairs show, English /t/ and /d/ are contrastive in initial and final position. In certain dialects (e.g., North American), this contrast is neutralized in some intervocalic environments, so that although bet and bed are pronounced differently, betting and bedding may be homophonous. Both lexical /t/ and lexical /d/ are produced as flaps (here transcribed [D]), involving ballistic tongue movement with extremely brief articulation of the tongue tip with the alveolar ridge (see De Jong [1]). Because there exist alternations (e.g., be[t] in bbetQ and be[D]- in bbettingQ), contrastive lexical representations are recoverable even if the contrast is neutralized on the surface. Ordinarily, a gradient repertoire for production ranging from fully contrastive to fully neutralized is available to adults. Structural and nonstructural factors determine the choice of contrast vs. neutralization, including the pragmatically based perceived need to contrast words. This study addressed the question of whether this type of knowledge is also shared by children who use cochlear implants (CIs). 2. Method Participants were seven adults with normal hearing, seven children with normal hearing, and seven children who used cochlear implants (CIs). Adults had to have English as a native language and normal hearing and speech. This group included five males and two females, ranging in age from 24;0 (years;months) to 27;9 (M=25;1). Children with normal hearing had to be between 7 and 12 years old and have normal hearing and speech and English as a native language. This group included five males and two females, ranging in age from 8;4 to 12;2 (M=10;4). Children who used CIs had to have at least 5 years of implant use and the ability to read aloud from printed text. They ranged in age from 8;9 to 19;8 (M=12;9). Age at implantation surgery ranged from 1;5 to 9;11 (M=5;0); length of implant use ranged from 5;0 to 14;9 (M=8;5). Materials for reading aloud were three lists containing three minimal pairs differing in lexical /t/ and /d/: betting/bedding, butting/budding, seating/seeding. The three lists represented three conditions differing in explicitness of the /t/ vs. /d/ contrast. In the Neutralization Condition (Condition 1), test words and distracters were embedded in carrier sentences such as Sheets, blankets, and pillows are BEDDING. Condition 1 minimized awareness of the /t/ vs. /d/ contrast, eliciting minimal phonetic differences between /t/ and /d/ (neutralized, flapped variants of both). In the Implicit Contrast Condition (Condition 2), test words (and distracters) were presented near each other without carrier sentences (e.g., betting/bedding) creating an awareness of the /t/ vs. /d/ contrast. In the Explicit Contrast Condition (Condition 3), only test words were used. The members of each pair were juxtaposed, emphasizing the contrast and the need to implement that contrast, for example, I didn’t say BETTING; I said BEDDING. For each test word, a spectrogram was generated on which three durations were measured: (a) the vowel preceding the /t, d/: the interval from the onset of periodic pulsing to the sudden drop in amplitude indicating closure; (b) the stop occlusion: the interval from the sudden drop in amplitude to the release burst; and (c) the voice onset time following stop release: the interval from the burst to the onset of period pulsing. Based on expected measurements, the following calculations were performed: (a) for the preceding vowel, the
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Fig. 1. Mean ratio of lexical /d/ to lexical /t/ for preceding vowel duration for the three participant groups across three conditions.
mean /d/-to-/t/ ratio; (b) for the stop occlusion, the mean /t/-to-/d/ ratio; and (c) for voice onset time, the mean arithmetic difference /t/ minus /d/. 3. Results Fig. 1 shows the mean ratio of lexical /d/ to lexical /t/ for the preceding vowel for each participant group across the three conditions. Adults with normal hearing had a d/t ratio close to 1.0 in Condition 1, with increases to Conditions 2 and 3. Both groups of children had higher d/t ratios in Condition 1 than the adults. Children with normal hearing increased the ratio slightly to Condition 2 and plateaued to Condition 3. Children with CIs decreased from Condition 1 to Condition 2, and then plateaued to Condition 3. Fig. 2 shows the mean t/d ratio for the stop occlusion duration for each group across the three conditions. Adults with normal hearing had a low t/d ratio in Condition 1, with a monotonic increase through Conditions 2 and 3. Both groups of children had higher ratios in Condition 1 than adults. Children with normal hearing maintained a stable ratio throughout; children with CIs increased the ratio through Conditions 2 and 3. Fig. 3 shows the mean arithmetic difference between voice onset times (VOTs) for lexical /t/ and /d/ for group across the three conditions. Adults with normal hearing exhibited a small difference between /t/ and /d/ in Condition 1, followed by a steep and consistent increase through Conditions 2 and 3. Both groups of children showed larger t/d
Fig. 2. Mean ratio of lexical /t/ to lexical /d/ for stop occlusion duration for the three participant groups across three conditions.
S.B. Chin, J.E. Krug / International Congress Series 1273 (2004) 328–331
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Fig. 3. Mean difference lexical /t/ minus lexical /d/ for voice onset time for the three participant groups across three conditions.
differences in Condition 1 than adults. Children with normal hearing increased the difference markedly in Condition 3, whereas children with cochlear implants maintained a similar difference throughout all three conditions. 4. Discussion For all measures, adults with normal hearing showed the smallest differences between lexical /t/ and /d/ in the neutralization condition and the most consistent increases in differences as the need to contrast increased. Both groups of children maintained relatively large differences between /t/ and /d/ on all measures (with values in Condition 1 often approximately equal to those of Condition 2 for the adults), and responses to the increase in perceived need to contrast were not uniform. These results indicate that adults with normal hearing have knowledge of both fully contrastive and neutralized variants of phonemes and are able to implement them phonetically in response to different pragmatic conditions. The two groups of children, on the other hand, did not exhibit such knowledge, tending to avoid neutralized productions and instead maintaining relatively contrastive productions throughout. These results are consistent with reports in the literature (e.g., Klein and Altman [2]) indicating that intervocalic variants of /t/ and /d/ (e.g., flaps) are acquired relatively late. The children with cochlear implants showed the largest /t/ vs. /d/ differences for all three parameters, particularly in Condition 1. This fact and the larger age range of these children may indicate generally a reduced repertoire (relative to adults and children with normal hearing) of structurally and nonstructurally determined phonological variants for children who use cochlear implants. Acknowledgements This work was supported by the following grants from the National Institutes of Health to Indiana University: R01DC005594, R03DC003852, T32DC00012. References [1] K. de Jong, Stress-related variation in the articulation of coda alveolar stops: flapping revisited, J. Phon. 26 (1998) 283 – 310. [2] H.B. Klein, E.K. Altman, The acquisition of medical /t,d/ allophones in bisyllabic contexts, Clin. Linguist. Phon. 16 (2002) 215 – 232.
www.ics-elsevier.com
Phonological contrast and neutralization by children with cochlear implants Steven B. Chin*, Joseph E. Krug Department of Otolaryngology, Indiana University School of Medicine, 699 West Dr., RR044, Indianapolis, IN 46202-5119, USA
Abstract. Objective: To determine the degree to which pediatric users of cochlear implants (CIs) implement neutralization of the /t/ vs. /d/ contrast under different pragmatic conditions. Study design: Children who used cochlear implants and both children and adults with normal hearing produced minimal pairs contrasting lexical /t/ and /d/ in three conditions that gradually increased the need to differentiate members of the pairs, ranging from neutralization through implicit contrast to explicit contrast. Duration of the preceding vowel, the stop occlusion, and voice onset time following release were measured. Results: Adults exhibited small differences between /t/ and /d/ in the neutralization condition; differences increased through the remaining conditions. For the children, differences between /t/ and /d/ in the neutralization condition were relatively large, and differences between /t/ and /d/ did not increase monotonically through the conditions. Conclusion: Adults with normal hearing implement contrast and neutralization depending on pragmatic context. Children with either normal hearing or cochlear implants exhibit less differentiation, tending to maintain contrastiveness regardless of pragmatic condition. D 2004 Elsevier B.V. All rights reserved.
Keywords: Cochlear implantation; Language acquisition; Phonological contrast; Phonological neutralization
1. Introduction Contrast is the property of language whereby sound segments can differentiate the meanings of lexical items. Minimal pairs of words, such as ten vs. den and bet vs. bed indicate a contrast between /t/ and /d/ in English, because the differences in meaning derive solely from the fact that one word has /t/ where the other has /d/ (all other phonetic material, -en or be-, being identical). Another property is that contrasts can be obliterated, * Corresponding author. Tel.: +1 317 274 4981; fax: +1 317 274 4949. E-mail address: [email protected] (S.B. Chin). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.08.004
S.B. Chin, J.E. Krug / International Congress Series 1273 (2004) 328–331
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or neutralized, in specific phonetic environments. As the cited minimal pairs show, English /t/ and /d/ are contrastive in initial and final position. In certain dialects (e.g., North American), this contrast is neutralized in some intervocalic environments, so that although bet and bed are pronounced differently, betting and bedding may be homophonous. Both lexical /t/ and lexical /d/ are produced as flaps (here transcribed [D]), involving ballistic tongue movement with extremely brief articulation of the tongue tip with the alveolar ridge (see De Jong [1]). Because there exist alternations (e.g., be[t] in bbetQ and be[D]- in bbettingQ), contrastive lexical representations are recoverable even if the contrast is neutralized on the surface. Ordinarily, a gradient repertoire for production ranging from fully contrastive to fully neutralized is available to adults. Structural and nonstructural factors determine the choice of contrast vs. neutralization, including the pragmatically based perceived need to contrast words. This study addressed the question of whether this type of knowledge is also shared by children who use cochlear implants (CIs). 2. Method Participants were seven adults with normal hearing, seven children with normal hearing, and seven children who used cochlear implants (CIs). Adults had to have English as a native language and normal hearing and speech. This group included five males and two females, ranging in age from 24;0 (years;months) to 27;9 (M=25;1). Children with normal hearing had to be between 7 and 12 years old and have normal hearing and speech and English as a native language. This group included five males and two females, ranging in age from 8;4 to 12;2 (M=10;4). Children who used CIs had to have at least 5 years of implant use and the ability to read aloud from printed text. They ranged in age from 8;9 to 19;8 (M=12;9). Age at implantation surgery ranged from 1;5 to 9;11 (M=5;0); length of implant use ranged from 5;0 to 14;9 (M=8;5). Materials for reading aloud were three lists containing three minimal pairs differing in lexical /t/ and /d/: betting/bedding, butting/budding, seating/seeding. The three lists represented three conditions differing in explicitness of the /t/ vs. /d/ contrast. In the Neutralization Condition (Condition 1), test words and distracters were embedded in carrier sentences such as Sheets, blankets, and pillows are BEDDING. Condition 1 minimized awareness of the /t/ vs. /d/ contrast, eliciting minimal phonetic differences between /t/ and /d/ (neutralized, flapped variants of both). In the Implicit Contrast Condition (Condition 2), test words (and distracters) were presented near each other without carrier sentences (e.g., betting/bedding) creating an awareness of the /t/ vs. /d/ contrast. In the Explicit Contrast Condition (Condition 3), only test words were used. The members of each pair were juxtaposed, emphasizing the contrast and the need to implement that contrast, for example, I didn’t say BETTING; I said BEDDING. For each test word, a spectrogram was generated on which three durations were measured: (a) the vowel preceding the /t, d/: the interval from the onset of periodic pulsing to the sudden drop in amplitude indicating closure; (b) the stop occlusion: the interval from the sudden drop in amplitude to the release burst; and (c) the voice onset time following stop release: the interval from the burst to the onset of period pulsing. Based on expected measurements, the following calculations were performed: (a) for the preceding vowel, the
330
S.B. Chin, J.E. Krug / International Congress Series 1273 (2004) 328–331
Fig. 1. Mean ratio of lexical /d/ to lexical /t/ for preceding vowel duration for the three participant groups across three conditions.
mean /d/-to-/t/ ratio; (b) for the stop occlusion, the mean /t/-to-/d/ ratio; and (c) for voice onset time, the mean arithmetic difference /t/ minus /d/. 3. Results Fig. 1 shows the mean ratio of lexical /d/ to lexical /t/ for the preceding vowel for each participant group across the three conditions. Adults with normal hearing had a d/t ratio close to 1.0 in Condition 1, with increases to Conditions 2 and 3. Both groups of children had higher d/t ratios in Condition 1 than the adults. Children with normal hearing increased the ratio slightly to Condition 2 and plateaued to Condition 3. Children with CIs decreased from Condition 1 to Condition 2, and then plateaued to Condition 3. Fig. 2 shows the mean t/d ratio for the stop occlusion duration for each group across the three conditions. Adults with normal hearing had a low t/d ratio in Condition 1, with a monotonic increase through Conditions 2 and 3. Both groups of children had higher ratios in Condition 1 than adults. Children with normal hearing maintained a stable ratio throughout; children with CIs increased the ratio through Conditions 2 and 3. Fig. 3 shows the mean arithmetic difference between voice onset times (VOTs) for lexical /t/ and /d/ for group across the three conditions. Adults with normal hearing exhibited a small difference between /t/ and /d/ in Condition 1, followed by a steep and consistent increase through Conditions 2 and 3. Both groups of children showed larger t/d
Fig. 2. Mean ratio of lexical /t/ to lexical /d/ for stop occlusion duration for the three participant groups across three conditions.
S.B. Chin, J.E. Krug / International Congress Series 1273 (2004) 328–331
331
Fig. 3. Mean difference lexical /t/ minus lexical /d/ for voice onset time for the three participant groups across three conditions.
differences in Condition 1 than adults. Children with normal hearing increased the difference markedly in Condition 3, whereas children with cochlear implants maintained a similar difference throughout all three conditions. 4. Discussion For all measures, adults with normal hearing showed the smallest differences between lexical /t/ and /d/ in the neutralization condition and the most consistent increases in differences as the need to contrast increased. Both groups of children maintained relatively large differences between /t/ and /d/ on all measures (with values in Condition 1 often approximately equal to those of Condition 2 for the adults), and responses to the increase in perceived need to contrast were not uniform. These results indicate that adults with normal hearing have knowledge of both fully contrastive and neutralized variants of phonemes and are able to implement them phonetically in response to different pragmatic conditions. The two groups of children, on the other hand, did not exhibit such knowledge, tending to avoid neutralized productions and instead maintaining relatively contrastive productions throughout. These results are consistent with reports in the literature (e.g., Klein and Altman [2]) indicating that intervocalic variants of /t/ and /d/ (e.g., flaps) are acquired relatively late. The children with cochlear implants showed the largest /t/ vs. /d/ differences for all three parameters, particularly in Condition 1. This fact and the larger age range of these children may indicate generally a reduced repertoire (relative to adults and children with normal hearing) of structurally and nonstructurally determined phonological variants for children who use cochlear implants. Acknowledgements This work was supported by the following grants from the National Institutes of Health to Indiana University: R01DC005594, R03DC003852, T32DC00012. References [1] K. de Jong, Stress-related variation in the articulation of coda alveolar stops: flapping revisited, J. Phon. 26 (1998) 283 – 310. [2] H.B. Klein, E.K. Altman, The acquisition of medical /t,d/ allophones in bisyllabic contexts, Clin. Linguist. Phon. 16 (2002) 215 – 232.