Organization of babbling: a case study

Speech is probably the most complex serially ordered behavior in living forms. However, no systematic investigation of the organization of speech-related output when it is presumably simplest, namely during the babbling stage, has been attempted. Transcriptions of 423 babbled utterances (1145 syllables) were obtained from one subject 7-12 months of age. Most results could be interpreted in terms of a basic mouth opening-closing alternation, responsible not only for the typical vowel-consonant alternation of babbling, but also for many prominent details including within-utterance variation in vowel height (often stress-related) and in degree of closure for consonants. The results suggest that a "frame" for babbling is provided by mandibular oscillation, perhaps reflected, when operating alone, in the common alternation between labial consonants and central vowels. Variation in the amplitude of this oscillation may be responsible for the within-utterance vowel height and consonant manner variation and much of the perceived stress variation. Further variation is attributed to fronting movements of the tongue, the effects of which often spread beyond single vowels and consonants.