Verb Variability and Morphosyntactic Priming With Typically Developing 2- and 3-Year-Olds.

Purpose: This study was specifically designed to examine how verb variability and verb overlap in a morphosyntactic priming task affect typically developing children's use and generalization of auxiliary IS. Method: Forty typically developing 2- to 3-year-old native English-speaking children with inconsistent auxiliary IS production were primed with 24 present progressive auxiliary IS sentences. Half of the children heard auxiliary IS primes with 24 unique verbs (high variability). The other half heard auxiliary IS primes with only 6 verbs, repeated 4 times each (low variability). In addition, half of the children heard prime-target pairs with overlapping verbs (lexical boost), whereas the other half heard prime-target pairs with nonoverlapping verbs (no lexical boost). To assess use and generalization of the targeted structure to untrained verbs, all children described probe items at baseline and 5 min and 24 hr after the priming task. Results: Children in the high variability group demonstrated strong priming effects during the task and increased auxiliary IS production compared with baseline performance 5 min and 24 hr after the priming task, suggesting learning and generalization of the primed structure. Children in the low variability group showed no significant increases in auxiliary IS production and fell significantly below the high variability group in the 24-hr posttest. Verb overlap did not boost priming effects during the priming task or in posttest probes. Conclusions: Typically developing children do indeed make use of lexical variability in their linguistic input to help them extract and generalize abstract grammatical rules. They can do this quite quickly, with relatively stable, robust learning occurring after a single optimally variable input session. With reduced variability, learning does not occur.