The present study aimed at identifying the acoustic pattern of vocalizations, produced by 7-to 11-month-old infants, that were interpreted by their mothers as expressing emotions or communicative functions. Participants were 6 healthy, first-born English infants, 3 boys and 3 girls, and their mothers. The acoustic analysis of the vocalizations was performed using a pattern recognition (PR) software system. A PR system not only calculates signal features, it also automatically detects patterns in the arrangement of such features. The following results were obtained:(a) the PR system distinguished vocalizations interpreted as emotions from vocalizations interpreted as communicative functions with an overall accuracy of 87.34%;(b) the classification accuracy of the PR system for vocalizations that convey emotions was 85.4% and for vocalizations that convey communicative functions was 89.5%; and (c) compared to vocalizations that express emotions, vocalizations that express communicative functions were shorter, displayed lower fundamental frequency values, and had greater overall intensity. These findings suggest that in the second half of the first year, infants possess a vocal repertoire that contributes to regulating cooperative interaction with their mothers, which is considered one of the major prerequisites for language acquisition.

The ability of infants, before the emergence of language, to communicate different kinds of messages through nonlinguistic aspects of voice can be investigated by examining whether vocalizations that have been classified in different message categories exhibit distinct acoustic features. Relevant studies have focused mainly on vocal expressions of the first 6 months of life and demonstrated that vocalizations classified by mothers as cry, discomfort, calm, pleasure, or surprise exhibit distinct acoustic patterns (Hsu, Fogel, & Cooper, 2000; Papousek, 1992; Petrovich-Bartell, Cowan, & Morse, 1982; Scherer, 1984; Shimura & Imaizumi, 1995; Stark, Rose, & McLagen, 1975; Trainor, Austin, & Desjardins, 2000).