Children use speaker knowledge to learn novel subordinate vs. basic-level nouns

Children typically prefer the so-called "basic"-level (e.g., dog) versus narrower subordinate (e.g., dalmatian) meanings in acquisition. Subordinate conjectures are facilitated by contrast; for example, when shown a dalmatian and a corgi each labelled "dax" and "wug," learners take "dax" to mean dalmatian, as opposed to dog. But what is the nature of this effect? On a pragmatic account, contrast is helpful because it highlights a communicative pressure on the speaker to be more informative than usual when describing the target referent, given relevant alternatives. Another possibility, however, is that contrastive forms create a simple lexical heuristic. We raise and test two predictions that follow from the pragmatic, but not the lexical, account: in learning subordinate nouns, children use contrastive information even when there are no competing lexical labels (Exp. 1); furthermore, they consider the speaker's knowledge of contrasting alternatives during word learning, as a fully Gricean rich-computation model expects (Exp. 2). Results support a pragmatic (over a purely lexical) account of subordinate conjectures. Thus subordinate noun learning offers an early demonstration of children's ability to integrate informativeness with the speaker's epistemic state during word learning.