Infants' Ability to Learn Phonetically Similar Words: Effects of Age and Vocabulary Size

What do novice word learners know about the sound of words? Word-learning tasks suggest that young infants (14 months old) confuse similar-sounding words, whereas mispronunciation detection tasks suggest that slightly older infants (18-24 months old) correctly distinguish similar words. Here we explore whether the difficulty at 14 months stems from infants' novice status as word learners or whether it is inherent in the task demands of learning new words. Results from 3 experiments support a developmental explanation. In Experiment 1, infants of 20 months learned to pair 2 phonetically similar words to 2 different objects under precisely the same conditions that infants of 14 months (Experiment 2) failed. In Experiment 3, infants of 17 months showed intermediate, but still successful, performance in the task. Vocabulary size predicted word-learning performance, but only in the younger, less experienced word learners. The implications of these results for theories of word learning and lexical representatio...