McCathren et al.: Vocalization 915 Rebecca B. McCathren University of Missouri Columbia Paul J. Yoder Steven F. Warren Vanderbilt University Nashville, TN This study tested the relationship between prelinguistic vocalization and expres- sive vocabulary 1 year later in young children with mild to moderate develop- mental delays. Three vocalization variables were tested: rate of all vocalization, rate of vocalizations with consonants, and rate of vocalizations used interactively. The 58 toddlers in the study were 17–34 months old, not sensory impaired, and had Bayley Mental Development Indices (Bayley, 1969; Bayley, 1993) from 35– 85. In addition, the children had fewer than 3 words in their expressive vocabu- laries and during classroom observation each showed at least one instance of intentional prelinguistic communication before testing. Selected sections of the Communication and Symbolic Behavior Scales procedures (CSBS; Wetherby & Prizant, 1993) were administered at the beginning and at the end of the study. The vocal measures were obtained in the initial CSBS session. One measure of expressive vocabulary was obtained in the CSBS session at the end of the study. In addition, expressive vocabulary was measured in a nonstructured play session at the end of the study. We predicted that rate of vocalization, rate of vocalizations with consonants, and rate of vocalizations used interactively would all be positively related to later expressive vocabulary. The results confirmed the predictions. KEY W ORDS: prelinguistic communication, vocalization, communication development, developmental delay The Relationship Between Prelinguistic Vocalization and Later Expressive Vocabulary in Young Children With Developmental Delay Journal of Speech, Language, and Hearing Research • Vol. 42 • 915–924 • August 1999 • ©American Speech-Language-Hearing Association 915 1092-4388/ 99/ 4204-0915 O ne of the more extensively studied areas of prelinguistic be- havior is vocal development. More than 50 years ago research- ers were investigating the relationship between babbling and spoken language (Jakobson, 1941; Lewis, 1936). Researchers have contin- ued to investigate vocalization in infants to determine the continuities between vocalization and later speech and to see if spoken language devel- opment can be predicted from aspects of prelinguistic vocalization (Kagan, 1971; Locke, 1989; Roe, 1977; Stoel-Gammon, 1989, 1992). Relationship Between Babbling and Spoken Language A number of hypotheses have been formulated to explain the conti- nuities between prelinguistic vocalization and later spoken language.