Developmental and Individual Differences in the Timecourse of Prior Knowledge and Offline Consolidation Support in the Vocabulary Learning of Adults and Children

Vocabulary is a fundamental component in communication and literacy development. This thesis investigated when prior semantic knowledge and memory consolidation support vocabulary learning, characterising developmental and individual differences in these mechanisms. Existing research suggests children’s word learning benefits more from memory consolidation, potentially underpinned by developmental differences in sleep architecture, whereas adults benefit from a mature language system and greater prior knowledge. The thesis addresses the possible sources of this developmental difference by comparing the learning trajectory of children aged 9 to 11 and adults across one week. To test the role of specific connections with prior knowledge, novel words were paired with pictures providing strong local connections with real animals or weak connections through fictitious creatures, and abstract patterns with no semantics. Across five experiments, word form recall was tested immediately and after a one-week delay, with an additional test after a 10-minute or 1-day delay. Semantic benefits enhanced adults’ word recall, especially in tasks that demand form-meaning retrieval, from the immediate test and were maintained across delays; but children showed no prior knowledge benefit. Whereas children showed particular benefits from offline consolidation, during which their memory improved over tests spanning nocturnal sleep, but not over daytime rest. Adults showed a smaller consolidation effect, especially in the absence of reconsolidation opportunities from interleaved tests. Direct developmental comparisons demonstrated children’s superior improvements across periods of offline consolidation. Global linguistics skills predicted the overall word recall across test points of children and in more diverse adult samples but did not influence the extent to which local semantic connections could be benefited. This thesis demonstrates developmental stability and changes in the mechanisms that underpin word learning: Children rely more on offline consolidation processes whilst adults benefit more from local semantic connections, but both can benefit from global linguistic skills.