Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland, USA.
New Glarus School District, New Glarus, Wisconsin, USA.
Ear Hear. 2022 Mar/Apr;43(2):519-530. doi: 10.1097/AUD.0000000000001115.
The present study investigated how development of the /t/-/k/ contrast is affected by the unique perceptual constraints imposed on young children using cochlear implants (CIs). We hypothesized that children with CIs would demonstrate unique patterns of speech acquisition due to device limitations, rather than straightforward delays due to a lack of auditory input in the first year of life before implantation. This study focused on the contrast between /t/ and /k/ because it is acquired early in the sequence of development, requires less advanced motor control than later-acquired place contrasts, is differentiated by spectral cues (which are particularly degraded when processed by CIs), and is not easily differentiated by visual cues alone. Furthermore, perceptual confusability between /t/ and /k/ may be exacerbated in front-vowel contexts, where the spectral energy for /k/ is shifted to higher frequencies, creating more spectral overlap with /t/.
Children with CIs (n = 26; ages 31 to 66 mo) who received implants around their first birthdays were matched to peers with normal hearing (NH). Children participated in a picture-prompted auditory word-repetition task that included over 30 tokens of word-initial /t/ and /k/ consonants. Tokens were balanced across front-vowel and back-vowel contexts to assess the effects of coarticulation. Productions were transcribed and coded for accuracy as well as the types of errors produced (manner of articulation, voicing, or place of articulation errors). Centroid frequency was also calculated for /t/ and /k/ tokens that were produced correctly. Mixed-effects models were used to compare accuracy, types of errors, and centroid frequencies across groups, target consonants, and vowel contexts.
Children with CIs produced /t/ and /k/ less accurately than their peers in both front- and back-vowel contexts. Children with CIs produced /t/ and /k/ with equal accuracy, and /k/ was produced less accurately in front-vowel contexts than in back-vowel contexts. When they produced errors, children with CIs were more likely to produce manner errors and less likely to produce voicing errors than children with NH. Centroid frequencies for /t/ and /k/ were similar across groups, except for /k/ in front-vowel contexts: children with NH produced /k/ in front-vowel contexts with higher centroid frequency than children with CIs, and they produced /k/ and /t/ with equal centroid frequencies in front-vowel contexts.
Children with CIs not only produced /t/ and /k/ less accurately than peers with NH, they also demonstrated idiosyncratic patterns of acquisition, likely resulting from receiving degraded and distorted spectral information critical for differentiating /t/ and /k/. Speech-language pathologists should consider perceptual confusability of consonants (and their allophonic variations) during their assessment and treatment of this unique population of children.
本研究旨在探讨在使用人工耳蜗（CI）时，儿童独特的感知限制如何影响 /t/-/k/ 对比的发展。我们假设，由于设备限制，植入前一年缺乏听觉输入，而不是由于直接延迟，植入 CI 的儿童的言语习得会呈现出独特的模式。本研究集中于 /t/ 和 /k/ 之间的对比，因为它在发育序列中较早获得，需要比后期获得的位置对比更少的高级运动控制，通过频谱线索区分（这些线索在被 CI 处理时特别退化），并且不能仅通过视觉线索轻松区分。此外，/t/ 和 /k/ 之间的感知混淆可能在前元音语境中加剧，其中 /k/ 的频谱能量转移到更高的频率，从而与 /t/ 产生更多的频谱重叠。
在他们一岁生日左右接受植入物的 CI 儿童（n=26；年龄 31 至 66 个月）与具有正常听力（NH）的同龄人相匹配。儿童参加了图片提示的听觉单词重复任务，其中包括超过 30 个单词起始的 /t/ 和 /k/ 辅音。在前后元音语境中平衡代币，以评估协同发音的影响。转录和编码发音的准确性以及产生的错误类型（发音方式、发声或发音位置错误）。还为正确产生的 /t/ 和 /k/ 代币计算了质心频率。使用混合效应模型比较组间、目标辅音和元音语境的准确性、错误类型和质心频率。
在前后元音语境中，CI 儿童的 /t/ 和 /k/ 发音准确性均低于其同龄人。CI 儿童的 /t/ 和 /k/ 发音准确度相等，/k/ 在前元音语境中的发音准确性低于后元音语境。当他们犯错时，CI 儿童比 NH 儿童更有可能产生发音方式错误，而不太可能产生发声错误。除了前元音语境中的 /k/ 之外，各组的质心频率相似：NH 儿童在前元音语境中产生的 /k/ 质心频率高于 CI 儿童，而他们在前元音语境中产生的 /k/ 和 /t/ 质心频率相等。
CI 儿童不仅比具有 NH 的同龄人更不准确地产生 /t/ 和 /k/，而且还表现出独特的习得模式，这可能是由于接受了区分 /t/ 和 /k/ 的关键的退化和扭曲的频谱信息。言语语言病理学家在评估和治疗这一独特的儿童群体时，应考虑辅音的感知混淆（及其变音）。
