Thus, the language learning process is bi-directional with the parent’s behavior affecting the child and the child’s behaviors affecting the parent, with both moving in unison to lay a foundation for subsequent language acquisition. Several randomized controlled studies have documented differential effects of language intervention approaches for young children with DD that focus on both child and parent training to ensure high levels of responsiveness ( Yoder & Warren, 2002 2006 Yoder, Woynaroski, Fey & Warren, in press). These responsive strategies support more advanced language and vocabulary development in the child, with concomitant and more complex changes in parent language input ( Warren et al., 2008). For example, when children begin to use gestures and vocalize, parents tend to interpret these behaviors as communicative, imitate the child, and may assign meaning to the vocalizations using words. To the extent that child vocalizations continue to serve a communicative role in early interactions, it is important to also consider developmental trends in rates of vocalizations (inclusive of both speech and nonspeech vocalizations).Ī change in how a child vocalizes and communicates may lead to changes in parent responsiveness and conversely, highly responsive parents who follow their child’s lead and model language based on child interests may lead to positive changes in intentional child communication ( Yoder & Warren, 1998 2002). Alternatively, vocalizations could accelerate or decline based on environmental feedback (e.g., parent input or responsiveness). That is, although it is well documented that children with DS are significantly delayed in transitioning to spoken words, what happens to their rates of vocalizations? One might hypothesize that a child’s rate of vocalizations stays constant over a longer period of time, despite a lack of speech development. Little is known about the trajectories of vocalizations themselves. Thus, the picture that emerges as children with DS progress through the later period of early childhood (ages 2–5 yrs) is of a language developmental trajectory that appears to level out after age 2 years. These linguistic delays are chronic and difficult to ameliorate through intervention ( Abbeduto et al., 2007). Furthermore, expressive development appears to significantly lag behind the use of gestures and receptive development, and is typically delayed relative to developmental age, not just chronological age ( Caselli et al, 1998 Miller, 1992). There is a consensus in the literature that the subsequent onset of meaningful speech (e.g., first words) is delayed and proceeds at a much slower pace than typically developing children ( Abbeduto et al., 2007 Kumin, Councill, & Goodman, 1999 Ypsilanti, Grouios, Alevriadou, & Tsapkini, 2005). Unfortunately, the early success of children with DS slows considerably when they begin the transition to linguistic development. In short, research suggests that early communication of infants with DS, in relation to babbling and nonverbal skills, develops comparably to that of typical language learners at the same developmental stage ( Sterling & Warren, 2008). Furthermore, the overlapping emergence of nonverbal communication skills (e.g., use of gestures) is only marginally delayed ( Mundy, Sigman, Kasari, & Yirmiya, 1988).
Nevertheless, the age of onset of canonical babbling with a minimum of a single consonant/vowel speech-like production (e.g., ba) is only about 2 months behind typically developing (TD) infants on average ( Lynch, Oller, Steffens, & Levine, 1995 Nathani, Oller & Cobo-Lewis, 2003) and the onset of reduplicated babbling (e.g., “dadada”) in infants with DS has been reported to develop at the same time as for TD infants ( Smith & Oller, 1981). It is known, for example, that oral-motor problems in infants with DS often result in problems with the precise production of early speech sounds ( Spender et al., 1995 1996). Because DS is a common developmental disorder and is typically identified before or at birth, the research literature on the maturation of these children is relatively robust. These delays and disorders are usually apparent early in development. Delayed and disordered speech is among the hallmark features of Down syndrome (DS) ( Abbeduto, Warren & Conners, 2007).