Lexical Factors in Parental Speech Affecting Vocabulary Acquisition in Children With and Without Language Delay: Using the Speech Rating Scale System

Objectives: This study examined the influence of specific lexical factors-frequency, perceptual salience, and pronounceability-on vocabulary acquisition among preschool children. Particular attention was paid to identifying the differential effects between typically developing children and those with early language delays, with the broader aim of developing effective strategies for early language intervention.Methods: The participants included 27 children aged 4-6 years (10 with language delays and 17 with typical development) and their primary caregivers. Each caregiver recorded over 10 hours of spontaneous parent–child interactions in naturalistic settings using wearable recording devices. Speech samples were transcribed, speaker roles were clearly distinguished, and lexical features were analyzed using the Speech Rating Scale System. Words were categorized as either expressed or unexpressed by the children. Nonparametric statistical methods were applied to examine both within- and between-group differences in lexical characteristics, considering the data’s distributional properties.Results: In both groups, higher frequency and greater pronounceability of words were significantly associated with expressive vocabulary acquisition. Perceptual salience, operationalized as slower parental speech rate, was positively related to vocabulary acquisition only among typically developing children. Comparative analyses further revealed that children with language delay required substantially higher frequency of input to incorporate new vocabulary compared to their typically developing peers.Conclusion: These findings underscore the critical role of lexical properties in early word-learning and highlight that their influence varies depending on the child’s developmental status. These clinical implications suggest that emphasizing frequent, perceptually salient, and articulatorily simple words may effectively support vocabulary growth in children with language delay.