Successful Implicit Vocabulary Intervention for Three Cantonese-Speaking Toddlers: A Replicated Single-Case Design

Purpose We report on a replicated single-case design study that measured the feasibility of an expressive vocabulary intervention for three Cantonese-speaking toddlers with small expressive lexicons relative to their age. The aim was to assess the cross-cultural and cross-linguistic feasibility of an intervention method developed for English-speaking children. Method A nonconcurrent multiple-baseline design was used with four baseline data points and 16 intervention sessions per participant. The intervention design incorporated implicit learning principles, high treatment dosage, and control of the phonological neighborhood density of the stimuli. The children (24-39 months) attended 7-9 weeks of twice weekly input-based treatment in which no explicit verbal production was required from the child. Each target word was provided as input a minimum of 64 times in at least two intervention sessions. Treatment feasibility was measured by comparison of how many of the target and control words the child produced across the intervention period, and parent-reported expressive vocabulary checklists were completed for comparison of pre- and postintervention child spoken vocabulary size. An omnibus effect size for the treatment effect of the number of target and control words produced across time was calculated using Kendall's Tau. Results There was a significant treatment effect for target words learned in intervention relative to baselines, and all children produced significantly more target than control words across the intervention period. The effect of phonological neighborhood density on expressive word production could not be evaluated because two of the three children learned all target words. Conclusion The results provide cross-cultural evidence of the feasibility of a model of intervention that incorporated a high-dosage, cross-situational statistical learning paradigm to teach spoken word production to children with small expressive lexicons.