The relationship among receptive vocabulary, non-word repetition, and quick incidental learning in preschoolers with and without delay in vocabulary development

Objectives: The present study investigated whether children with normal language (NL) and children with delay in vocabulary development (VD) show difference in performance on non-word repetition and quick incidental learning (QUIL), whether these factors correlate with one another, and whether these factors could predict children's receptive vocabulary. Methods: The study included children between 2 to 6 years of age, 19 NL and 19 VD. The experiments consisted of two tasks: non-word repetition to measure phonological memory, and QUIL to measure vocabulary learning ability. We compared group performances on each task. We also investigated correlations among factors and predictors. Results: The results were as followed. There were significant differences between two groups on all two tasks showing that children with VD performed significantly lower than children with NL. In the VD group, receptive vocabulary correlated only with the non-word repetition task, whereas receptive vocabulary correlated with both non-word repetition and QUIL tasks in the NL group. The strongest factor which predicted children's receptive vocabulary was QUIL in NL group, whereas non-word repetition predicted VD group's receptive vocabulary the most. Conclusion: The results show that implicit learning ability could be the important factor only in young NL group when they learn receptive vocabularies. On the other hand, phonological short-term memory promotes receptive vocabulary learning in VD group. It indicates that children with VD inefficiently learn vocabularies compared to NL children, and if children with VD could facilitate implicit learning ability, it could result in effective vocabulary learning.