Purpose: To identify variability in word learning mechanisms used by late talking children using a longitudinal study design, which may explain variability in late talking children’s outcomes.
Method: A cohort of typically developing children (n = 40) and children who were classified as late talking children at age 2;0 (10th percentile on expressive vocabulary, n = 21) were followed up at age 3;0 and at age 3;6. We tested the cohort across tasks designed to isolate different mechanisms involved in word learning: encoding and producing spoken forms of words (using a nonword repetition task), identifying referents for words (using a fast mapping task), and learning associations between words and referents (using a cross-situational word learning task).
Results: Late talking children had lower accuracy on nonword repetition than typically developing children, despite most of the sample reaching typical ranges for expressive vocabulary at age 3;6. There were no between-group differences in fast mapping and retention accuracy, however, both were predicted by concurrent expressive vocabulary. Late talking children performed less accurately than typically developing children on cross-situational word learning retention trials, despite showing no between-group differences during training trials. Combining performance across all three tasks predicted approximately 45% of the variance in vocabulary outcomes at the last timepoint.
Conclusions: Late talking children continue to have deficits in phonological representation that impact their word learning ability and expressive language abilities, but do not show difficulties in fast mapping novel words. Late talking children may also struggle to retain associative information about word-referent mappings. Late talking children thus use some, but not all, word learning mechanisms differently than typically developing children.