Covert contrast in velar fronting: An acoustic and ultrasound study.

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

越来越多的证据表明，语音习得是一个渐进的过程，仪器测量经常揭示出在被认为涉及音位替换的错误中存在隐性对比。超声成像有可能通过显示儿童在发出被认为是中和的声音时是否使用不同的舌形来扩展我们对隐性对比的理解。本研究使用超声测量（舌背位移指数）和声学测量（声门关闭时间以及爆破音的频谱矩）来研究儿童语音中软腭音和齿龈音塞音之间的显性和隐性对比。参与者是两名产生可感知的显性软腭 - 齿龈对比的儿童和两名通过软腭前置使对比中和的儿童。声学和超声测量都揭示了在可感知的不同软腭音和齿龈音目标之间存在显著差异。一名软腭前置的儿童在一项声学测量和一项超声测量中显示出隐性对比；另一名则没有对比的迹象。文中还讨论了临床意义。