Speech Development Between 30 and 119 Months in Typical Children I: Intelligibility Growth Curves for Single-Word and Multiword Productions

Abstract

Purpose We extended our earlier study on normative growth curves for intelligibility development in typical children from 30 to 119 months of age. We also determined quantile-specific age of steepest growth and growth rates. A key goal was to establish age-specific benchmarks for single-word and multiword intelligibility. Method This cross-sectional study involved collection of in-person speech samples from 538 typically developing children (282 girls and 256 boys) who passed speech, language, and hearing screening measures. One thousand seventy-six normal-hearing naïve adult listeners (280 men and 796 women) orthographically transcribed children's speech. Speech intelligibility was measured as the percentage of words transcribed correctly by naive adults, with single-word and multiword intelligibility outcomes modeled separately. Results The age range for 50% single-word intelligibility was 31–47 months (50th–5th percentiles), the age range for 75% single-word intelligibility was 49–87 months, and the age range for 90% intelligibility for single words was 83–120+ months. The same milestones were attained for multiword intelligibility at 34–46, 46–61, and 62–87 months, respectively. The age of steepest growth for the 50th percentile was 30–31 months for both single-word and multiword intelligibility and was later for children in lower percentiles. The maximum growth rate was 1.7 intelligibility percentage points per month for single words and 2.5 intelligibility percentage points per month for multiword intelligibility. Conclusions There was considerable variability in intelligibility development among typical children. For children in median and lower percentiles, intelligibility growth continues through 9 years. Children should be at least 50% intelligible by 48 months.

Speech Development Between 30 and 119 Months in Typical Children II: Articulation Rate Growth Curves

“…One explanation for this difference is that children in the higher percentiles begin with faster articulation rates and therefore do not have as far to advance before becoming adultlike. This same phenomenon was observed in our companion study of speech intelligibility (Hustad et al, 2021).…”

“…The companion study focusing on speech intelligibility development (Hustad et al, 2021) All children were from the upper midwestern region of the United States, and their demographic characteristics reflect those of Wisconsin. Table 1 shows demographic information for the children.…”

“…This article is the second in a series examining developmental change in speech production for typical children between preschool and middle childhood. In the first paper (Hustad et al, 2021), we examine speech intelligibility development for single words and connected speech for a large cross-sectional group of children, generating percentile growth curves and quantifying the effects of utterance length on intelligibility by age. In the present article, we examine parallel data on the developmental change in articulation rate, creating percentile growth curves and quantifying a Department of Communication Sciences and Disorders, University of Wisconsin-Madison b the effects of utterance length on articulation rate.…”

Utility of the Intelligibility in Context Scale for Predicting Speech Intelligibility of Children with Cerebral Palsy

“…Until very recently, comprehensive normative standards for characterizing intelligibility development in typical children did not exist. The most recent work, however, has provided a foundation for understanding growth trajectories between the ages of 2 and 10 years [ 8 , 9 , 10 ]. Results have indicated that children’s intelligibility grows rapidly in the preschool years and is highly variable.…”

“…Results have indicated that children’s intelligibility grows rapidly in the preschool years and is highly variable. Intelligibility continues to improve with age throughout middle childhood, and variability decreases with age [ 8 , 9 , 10 ]. Studies of typical speech intelligibility development provide an important foundation for interpreting intelligibility in children with dysarthria.…”