Title: Expected intelligibility decreases with speaking rate for younger children and longer utterances
Legend: Intelligibility as a function of speaking rate and age in different utterance lengths – Typically developing children produced 4-7-word utterances in a repetition task. We measured their speaking rate in syllables per second, and their intelligibility as the proportion of words correctly transcribed by two listeners. Points represent observed data with 1 point per child per panel. Lines represent the expected marginal mean for the central age in each age bin (i.e., age 3;0 for the 2;6-3;5 bin). Within each panel, we see the lines stacked in the expected order: Children become more intelligible with age. The vertical black line on each line is the median speaking rate for children in the age bin, and the thicker region of the line marks the 25%-75% percentile range. Within each panel, we see the medians move from left to right with age: Children’s habitual speaking rate increases with age. All the lines follow a flat or slightly negative slope, indicating that increases in speaking rate predict decreases in intelligibility. This effect is small to negligible in the three oldest age bins, but for younger children and for longer utterances, the trend suggests a speed-accuracy tradeoff for habitual speech production.
Citation: Mahr, T., Rathouz, P., & Hustad, K. C. (In prep.) Speech Development Between 30 and 119 Months in Typical Children III: Relationship between Intelligibility and Speaking Rate
Abstract: Prior work has documented how children’s intelligibility and articulation rate increased over the childhood years. We asked whether speaking rate influenced intelligibility in a sample of 538 typically developing children between ages 2;6 and 9;11 (years;months). Because utterance length can influence intelligibility (more words providing additional sentence context) and rate (more words requiring more efficient speech in a single fluent utterance), we stratified rate and intelligibility scores by utterance length. We found a small negative effect of speaking rate on intelligibility at younger ages for longer utterance lengths. For example, at age 4;0, an increase in rate of .5 syllables per second predicted a corresponding decrease in intelligibility of 3-5 percentage points on 5-7-word utterances. For shorter items or for children older than age 5, this rate effect is negligible. Implications will be discussed.
Slide Author: Tristan Mahr, PhD
Investigator: Katie Hustad, PhD
About the Lab: Katherine Hustad is professor and chair of Communication Sciences and Disorders. Her research examines speech and language development in children with cerebral palsy, with a focus on improving treatment decision-making, clinical outcomes, and quality of life. Visit the Wisconisn Intelligibility, Speech, and Communication (WISC) Lab for more information.
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