Rapid word learning in 13- and 17-month-olds in a naturalistic two-word procedure: looking versus reaching measures

This study investigated infants' rapid learning of two novel words using a preferential looking measure compared with a preferential reaching measure. In Experiment 1, 21 13-month-olds and 20 17-month-olds were given 12 novel label exposures (6 per trial) for each of two novel objects. Next, in the label comprehension tests, infants were shown both objects and were asked, "Where's the [label]?" (looking preference) and then told, "Put the [label] in the basket" (reaching preference). Only the 13-month-olds showed rapid word learning on the looking measure; neither age group showed rapid word learning on the reaching measure. In Experiment 2, the procedure was repeated 24h later with 10 participants per age group from Experiment 1. After a further 12 labels per object, both age groups now showed robust evidence of rapid word learning, but again only on the looking measure. This is the earliest looking-based evidence of rapid word learning in infants in a well-controlled (i.e., two-word) procedure; our failure to replicate previous reports of rapid word learning in 13-month-olds with a preferential reaching measure may be due to our use of more rigorous controls for object preferences. The superior performance of the younger infants on the looking measure in Experiment 1 was not straightforwardly predicted by existing theoretical accounts of word learning.