Predictors of Speech Ability in Down Syndrome

In most children, speech development progresses in a "seemingly automatic manner that continues from birth through adolescence"1 and supports related communication and reading abilities. But many individuals with Down Syndrome (DS, about 1 in 700 births in the US) struggle to acquire speech and participate more fully in human communication and gain access to learning experiences, in part, because their speech is often difficult to understand. This persistent speech disorder arises because people with DS must acquire and produce speech using structurally-different articulators and poor speech oral-motor abilities. Moreover, there is considerable variability in the speech intelligibility of people with DS and it is unclear why some people with DS communicate relatively proficiently whereas others are unable to clearly communicate.

The Investigator's recent research provides a unique combination of findings that, when integrated into a prospective project, can potentially provide new insights into how people with DS improve speech intelligibility. This assertion is grounded in the long-standing and replicated finding that speech intelligibility in DS is not strongly correlated with nor solely attributable to measures of phoneme production, so that improvements in intelligibility must rely not only improvements in speech accuracy (phoneme production) but also upon changes in "nonphonemic" factors such as cognitive-linguistic parameters and suprasegmental features such as prosody and speech rate that are currently poorly understood. For example, in a recent paper (Wilson, Abedduto, Camarata \& Shriberg, 2019), the Investigators describe cognitive/linguistic and speech-motor factors that relate to speech intelligibility in DS and provide preliminary data on nonphonemic parameters that are significantly correlated to intelligibility. In the cognitive linguistic domain, the Investigators found that measures of cognitive ability and receptive language abilities were directly related to speech intelligibility in people with DS. The Investigators also found that measures of speech-motor ability related to speech intelligibility. Importantly, in another series of studies, the Investigators demonstrated that individualized lexically based phonological recast intervention resulted in improvements in speech intelligibility in school age children with DS and that these gains were NOT uniquely attributable to changes in speech accuracy (phoneme production). Thus, the Investigators propose to induce growth in speech intelligibility in order to study change in speech and as an important step towards a) developing more effective speech interventions, and b) gaining a better understanding of parameters that drive improved speech intelligibility in DS (e.g.,phoneme production). This latter point is especially important because the Investigator's previous research and the extant literature indicate that traditional measures of speech accuracy (e.g., phoneme articulation) do not completely capture or predict improvements in speech intelligibility in DS. The proposed research would thus test assumptions underlying current models of speech disorder (and intervention) in DS. The Investigator's previous research has indicated that the Investigators can drive change in speech intelligibility without directly targeting speech accuracy, providing an opportunity to study intelligibility while controlling for speech accuracy as an untreated factor. Thus, an important first step in identifying factors that influence variation in speech intelligibility in addition to speech accuracy is to identify predictors of these speech abilities following intervention induced gains. Therefore, in keeping with the goals of an exploratory/developmental research project proposal (R21), the Investigators propose a pre-post design that measures speech intelligibility, and it's posited sequelae within the context of a controlled pre-post speech recast intervention study. Participants were 16 school-age children (4 to 17 years) with DS with varied cognitive ability levels (minimum of 60 with no ceiling). The following specific aims were pursued:

Aim 1: Test whether there were changes in baseline to post intervention measures of speech.

Aim 2: Examine the associations among measures of speech accuracy and prosody and overall speech intelligibility.

Impact: The results of this study within the context of a pre-post intervention design will provide important preliminary information on factors that contribute to intelligible speech in DS; thereby informing models of speech intelligibility and speech accuracy and future larger scale clinical trials. The proposed project will provide preliminary data to guide future longitudinal studies of value-added predictors of speech outcomes, and ultimately, improve assessment and intervention for speech deficits in individuals with DS.