When the daffodat flew to the intergalactic zoo: off-line consolidation is critical for word learning from stories

Previous studies using direct forms of vocabulary instruction have shown that newly learned words are integrated with existing lexical knowledge only after off-line consolidation (as measured by competition between new and existing words during spoken word recognition). However, the bulk of vocabulary acquisition during childhood occurs through incidental exposure to verbal material; hence, the role of consolidation may be different or limited when learning is less explicit. To address this, 40 children (ages 7-10 years) and 33 adults listened to a fictitious story that contained 12 novel words (e.g., "daffodat"). Lexical integration was measured by comparing pause detection latencies to existing competitors (e.g., "daffo_dil") and control words for which no new competitor had been encountered. Pause detection latencies were slower for existing competitors than control words (signifying increased lexical competition) 24 hr after exposure to the novel words but not immediately. Both groups recalled significantly more novel words when tested 24 hr after hearing the story than immediately. It is important that children with better expressive vocabulary knowledge showed larger consolidation effects for the novel words, both in terms of strengthening of explicit knowledge and their integration with existing knowledge. Off-line consolidation is therefore required for the integration of new and established knowledge when words are learned under relatively naturalistic conditions. Furthermore, a richer body of established vocabulary knowledge may facilitate (or benefit from) swift lexical integration of new vocabulary.