Sleep-associated changes in the mental representation of spoken words.

The integration of a newly learned spoken word form with existing knowledge in the mental lexicon is characterized by the word form's ability to compete with similar-sounding entries during auditory word recognition. Here we show that although the mere acquisition of a spoken form is swift, its engagement in lexical competition requires an incubation-like period that is crucially associated with sleep. Words learned at 8 p.m. do not induce (inhibitory) competition effects immediately, but do so after a 12-hr interval including a night's sleep, and continue to induce such effects after 24 hr. In contrast, words learned at 8 a.m. do not show such effects immediately or after 12 hr of wakefulness, but show the effects only after 24 hr, after sleep has occurred. This time-course dissociation is best accommodated by connectionist and neural models of learning in which sleep provides an opportunity for hippocampal information to be fed into long-term neocortical memory.