Substantial gains in word learning ability between 20 and 24 months: A longitudinal ERP study

This longitudinal ERP study investigated changes in children's ability to map novel words to novel objects during the dynamic period of vocabulary growth between 20 and 24 months. During this four-month period the children on average tripled their productive vocabulary, an increase which was coupled with changes in the N400 effect to pseudoword-referent associations. Moreover, productive vocabulary size was related to the dynamics of semantic processing during novel word learning. In children with large productive vocabularies, the N400 amplitude was linearly reduced during the five experimental learning trials, consistent with the repetition effect typically seen in adults, while in children with smaller vocabularies the N400 attenuation did not appear until the end of the learning phase. Vocabulary size was related only to modulation of the N400 to pseudowords, not to real words. These findings demonstrate a remarkable development of fast mapping ability between 20 and 24 months.