Development of Initial Clusters in American English by Fraternal Twins: An Acoustic Study

We investigate the phonological development of initial consonants and consonant clusters in a pair of fraternal female twins acquiring American English. At age 4 years, 1 month, twin A had achieved a nearly adult phonology; while twin B evidenced a reduced inventory of surface contrasts, due to the multiple effects of substitution, deletion, and coalescence. The relative intelligibility of twin B's speech leads one to wonder whether covert contrasts exist, that is, low-level phonetic differences which provide cues to the intended target forms. This question was investigated through an acoustic study with multiple repetitions of target forms, where measurements were made for duration, intensity, and spectral balance. Differences were found for both duration and intensity, providing further evidence of the role of covert contrast in phonological acquisition.