2.3: AAC modeling Rationale
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Language input is an important factor in child language acquisition (Gallway & Richards, 1994; Snow & Ferguson, 1978; Tomasello, 2003). During early childhood, children using speech are exposed to large levels of language input and interaction (Hart & Risley, 1995; Tomasello, 2003). The amount of words speaking children typically hear in their first four years ranges from approximately eight to 50 million words (Hart & Risley, 1995). Similarly to children who learn to communicate using speech, language input is important to children who use other expressive communication modalities as well, such as individuals with complex communication needs (CCN) who require augmentative and alternative communication (AAC). These individuals may communicate expressively using various modalities such as unaided AAC modalities such as sign languages, gestures, vocalizations, and speech, or aided AAC modalities such as with paper and computer based communication displays (e.g., iPad). The overall AAC language acquisition literature emphasizes the role of language input for individuals with CCN who require AAC (Beukelman & Mirenda, 2013). For example, research in sign language acquisition stresses the importance of language input, demonstrating that given appropriate sign language input, children can develop complex language abilities using sign language (Bavelier, Newport, & Supalla, 2003; Newport & Supalla, 2000).
Individuals with CCN who use aided AAC systems, such as those with picture or word systems that may be paper or computer based, also require appropriate language input (Beukelman & Mirenda, 2013; Romski & Sevcik, 1996). However, these individuals rarely observe models of AAC use, creating what Smith & Grove (2003) called an asynchrony of language input to output. That is, these individuals experience spoken language as input, but are expected to communicate expressively using AAC. Consequently, a number of AAC interventions have been developed in an attempt to provide this missing language input to individuals with CCN as a way to stimulate language gains (see single-subject meta-analysis; Sennott, Light, & McNaughton, 2014). For clarity and conciseness, Sennott et al. (2014) used the term AAC modeling to consolidate and describe the various types of language input provided through AAC modalities. Various AAC modeling intervention packages have positively impacted four different language areas: (a) pragmatics in the form of turn taking (e.g. Kent-Walsh, Binger, & Hasham, 2010); (b) semantics in the form of receptive and expressive vocabulary (e.g. Drager et al., 2006); (c) syntax in the form of increasing multi-symbol utterances (e.g. Binger, Kent-Walsh, Berens, Del Campo, & Rivera, 2008); and (d) morphology in the form of increased use of target structures (Binger, Maguire-Marshall, & Kent-Walsh, 2011). analysis results also indicated that because of the packaged nature of the interventions, parsing out modeling as the sole independent variable impacting student performance was difficult. In addition to the AAC modeling variable, time delay, and responding or recasting, were included in the majority of the reviewed packaged interventions. Those three intervention variables have been included in a newly designed intervention package called ModelER (Model, Encourage, Respond) for Read and Talk.