BACKGROUND AND AIMS: This longitudinal study investigated the language skills, phonological working memory and lexical-tone perception of Mandarin-speaking late-talkers (LTs) and those with typical language development (TLD) at 27 months, while also examining their connections with novel word-referent mapping (W-R mapping) through eye-tracking at 33 months.
METHODS AND PROCEDURES: Participants included 22 Mandarin-speaking 27-month-old LTs and 22 toddlers with TLD. Data on expressive and receptive language abilities, as well as phonological working memory and lexical-tone perception, were collected when participants were 27 months old. An eye-tracking paradigm was further employed during the word-learning tasks, which included W-R mapping and word-identification test (W-I test) phases at 33 months. Multilevel models were used to analyse participants' gaze pattern trajectories.
OUTCOMES AND RESULTS: At 27 months, LT toddlers exhibited poorer language skills (receptive: p = 0.015, expressive: p < 0.001), lexical-tone perception (p < 0.001) and phonological working memory (p < 0.001) compared to those with TLD, even after considering maternal educational level and participants' fine motor ability. During the W-I test phase, we observed that LT toddlers showed a slower increase in fixations on the novel target image while listening to the corresponding novel word over time, compared to TLD toddlers (linear: p = 0.011, quadratic: p = 0.007) after adding confounders. Further, expressive language ability at 27 months old was a predictor of their newly established W-R mappings at 33 months old (p = 0.016). Additionally, the toddler's phonological working memory and lexical-tone perception were associated with their expressive language ability (p = 0.001 and < 0.001).
CONCLUSIONS AND IMPLICATIONS: These findings indicate that the novel W-R mapping is not as robust in LTs as in TLDs, and the skills necessary for word learning share similarities with a wide range of expressive language abilities. Moreover, poor expressive language abilities were associated with deficits in lexical processing abilities; that is, phonological working memory and lexical-tone perception. These findings suggest the need for interventions aimed at improving LTs' lexical processing abilities to strengthen their lagging word-learning skills at toddlerhood.
WHAT THIS PAPER ADDS: What is already known on this subject Late-talkers (LTs) exhibit delays in expressive vocabulary development. Furthermore, they also perform poorly in word learning. What this paper adds to existing knowledge The eye-tracking paradigm was employed and found that novel word-referent mapping (W-R mapping) is not as robust in LTs as in those with typical language development. Toddlers' early expressive language ability could predict their ability to establish novel W-R mappings. Furthermore, the better the phonological working memory and lexical-tone perception of LTs are, the better their early expressive language ability is. What are the clinical implications of this work? Interventions might consider incorporating strategies to improve phonological working memory and lexical-tone perception to help Mandarin-speaking LTs enhance linguistic capacities and build robust novel W-R mapping.