Abstract
"Functional speech" by 5 years of age is widely established as increasing the probability of long-term positive outcomes across a range of domains for autistic individuals. While terms such as "functional" or "useful" speech are often used, what defines these terms is not well established. Furthermore, most research focusing on language development has emphasized the transition from little or no language to use of single words, but much less is known about the transition from single words to phrase speech, which could be equally important. The verb lexicon is foundational to the development of simple, generative phrases and has been linked to prosocial behaviors and general developmental outcomes including better social communication skills, socioemotional reciprocity, and nonverbal communication in autistic children. The current systematic review synthesized information from 20 independent samples to characterize autistic children who transitioned from single words to phrase speech. On average, 48% of the pooled sample transitioned to phrase speech during the study periods. Results were highly variable across studies. Participants under the age of 5 years were more likely to transition to phrases than participants over the age of 5. Though average standard scores were above 50, children who transitioned to phrases generally demonstrated below average adaptive and cognitive skills and moderate-high ASD symptomatology. Variable measures of cognition made it difficult to ascertain patterns in cognitive skills; nonetheless, nonverbal IQ emerged as a salient predictor of the transition to phrases across studies. More research is needed to better understand who transitions beyond single words, clinical benchmarks on the way to generative phrase speech and the factors that predict this transition. Such information can be used to inform clinical decision making and develop or improve targeted interventions based on individual communication profiles. This could make the use of phrases more likely for a greater number of autistic individuals, increasing the likelihood that these individuals communicate independently and effectively with others.