What Babies Know outlines a compelling case for why infancy research is fundamental for conceptualizing what it is to be human. There is another period in human development that is relatively inaccessible, yet is more important. In order to truly understand the nature of core knowledge, perception, and cognition, we must start not with the infant, but with the fetus.

This study adjudicates between two opposing accounts of morphological productivity, using English past-tense as its test case. The single-route model posits that both regular and irregular past-tense forms are generated by analogy across stored exemplars in associative memory. In contrast, the dual-route model posits that regular inflection requires use of a formal “add -ed” rule that does not require analogy across regular past-tense forms. Children saw animations of an animal performing a novel action described with a novel verb. Past-tense forms (...) of novel verbs were elicited by prompting the child to describe what the animal “did yesterday.” Collapsing across age group, the likelihood of a verb being produced in regular past-tense form was positively associated with the verb's similarity to existing regular verbs, consistent with the single-route model only. Results indicate that children's acquisition of the English past-tense is best explained by a single-route analogical mechanism that does not incorporate a role for formal rules. (shrink)