Speech Intelligibility Development of Children Aged 24 to 48 Months According to Listener's Familiarity with Child's Speech

Background & Objectives: Speech intelligibility is an important index for determining a child's verbal communication competence and the need for intervention and for evaluating the effectiveness of intervention. The present study investigated the developmental patterns of speech intelligibility based on single-word productions in typically developing children between 24 and 48 months of age according to listener's familiarity with child's speech. Methods: The participants in this study were 40 typically developing children that were divided into 4 age groups (6-month intervals, 10 children per group). The listener groups consisted of 40 children's mothers and 42 individuals who were not familiar with the child's speech. A picture list of 23 target words was presented to children who were asked to produce each target word spontaneously. Listeners listened to children's recorded speech samples and transcribed what they understood. Speech intelligibility was measured by dividing the number of fully intelligible target words by the total number of words and multiplying by 100. Results: 1) There were significant differences among the 4 different age groups in both listener groups. Post-hoc test revealed that speech intelligibility in the early 2-year-old group was significantly different from the late 2-year-old and early and late 3-year-old groups. Additionally, there was significant difference of speech intelligibility between the late 2-year-old group and late 3-year-old group. 2) There was no significant difference of speech intelligibility percentages between listener groups. Discussion & Conclusion: Speech intelligibility rapidly developed at 2 years of age and gradually progressed showing more than 70% of speech intelligibility after 3 years of age. The results suggested that listener's familiarity with a child's speech did not affect the speech intelligibility measures in single-word levels.