Children’s Expressive and Receptive Knowledge of the English Regular Plural

We investigate how children form early grammatical generalizations using the test case of the English regular plural. While some previous research provides evidence that children apply abstract rules to produce novel plurals well before 24mo., other studies have revealed that children use plural forms inconsistently with familiar and novel nouns, and demonstrate limited or variable receptive plural knowledge through (at least) 36mo. This is at odds with typical trajectories in child language development, where receptive knowledge precedes expressive. However, previous studies have not studied both receptive and expressive knowledge in the same children; additionally, differences in experimental materials across studies limit interpretability. In a cross-sectional design we tested 128 24-36-month-olds on two complementary experimental tasks: a receptive (eyetracking) task to evaluate children's understanding of plurals and an expressive (storybook) task to test their plural production. In the former, children heard sentences directing their gaze to an onscreen plural or singular target. In the latter, they heard a singular object labeled, and a prompt eliciting their plural production. We manipulated both novelty (novel vs. familiar object words, e.g., cats vs. wugs) and phonological form (/s/ vs. /z/ plurals, e.g., cats vs. dogs). We found strong, age-related evidence of expressive knowledge of the plural, but much more limited evidence of receptive knowledge (which was not predicted by age). Performance on the expressive task only predicted performance on the receptive task when additional grammatical cues were included (e.g., "there are two wugs" vs. "can you find the wugs?"). This work highlights the complexity of emerging grammatical generalizations in language acquisition and emphasizes the role of redundant grammatical cues in processing.