Rule invention in the acquisition of morphology by a language-impaired child

This paper presents a case study of a language-impaired child who invented a unique morphophonologic rule for signaling the distinction between English singular and plural nouns. Conventional linguistic-phonetic analysis indicated that the child was producing the distinction suprasegmentally rather than segmentally. Acoustic-phonetic analysis of matched singular-plural noun pairs was performed in order to determine quantitatively which suprasegmental acoustic cues he used to signal the distinction. Results of a multivariate analysis of variance revealed that singular and plural productions were significantly different from one another on various fundamental frequency, duration, and intensity parameters. This example of a child's linguistic creativity is offered as further evidence in support of a model of language acquisition that emphasizes the cognitive aspects underlying linguistic regularities in child language. Clinical implications are also discussed.