Infants listen for more phonetic detail in speech perception than in word-learning tasks.

Infants aged 4-6 months discriminate the fine phonetic differences that distinguish syllables in both their native and unfamiliar languages, but by 10-12 months their perceptual sensitivities are reorganized so that they discriminate only the phonetic variations that are used to distinguish meaning in their native language. It would seem, then, that infants apply their well honed phonetic sensitivities as they advance and begin to associate words with objects, but the question of how speech perception sensitivities are used in early word learning has not yet been answered. Here we use a recently developed technique to show that when they are required to pair words with objects, infants of 14 months fail to use the fine phonetic detail they detect in syllable discrimination tasks. In contrast, infants of 8 months--who are not yet readily learning words--successfully discriminate phonetic detail in the same task in which infants aged 14 months fail. Taken together, these results suggest a second reorganization in infants's use of phonetic detail as they move from listening to syllables to learning words.