Abstract
New vocabulary is consolidated offline, particularly during sleep; however, the parameters that influence consolidation remain unclear. Two experiments investigated effects of exposure level and delay between learning and sleep on adults' consolidation of novel competitors (e.g. BANARA) to existing words (e.g. BANANA). Participants made speeded semantic decisions (i.e. a forced choice: natural versus man-made) to the existing words, with the expectation that novel word learning would inhibit responses due to lexical competition. This competition was observed, particularly when assessed after sleep, for both standard and high exposure levels (10 and 20 exposures per word; Experiment 1). Using a lower exposure level (five exposures; Experiment 2), no post-sleep enhancement of competition was observed, despite evidence of consolidation when explicit knowledge of novel word memory was tested. Thus, when encoding is relatively weak, consolidation-related lexical integration is particularly compromised. There was no evidence that going to bed soon after learning is advantageous for overnight consolidation; however, there was some preliminary suggestion that longer gaps between learning and bed-onset were associated with better explicit memory of novel words one week later, but only at higher levels of exposure. These findings suggest that while lexical integration can occur overnight, weaker lexical traces may not be able to access overnight integration processes in the sleeping brain. Furthermore, the finding that longer-term explicit memory of stronger (but not weaker) traces benefit from periods of wake following learning deserves examination in future research.
Highlights
An accumulation of behavioural and neuroimaging research suggests that sleep is one state that actively supports the consolidation of a newly encountered word, and the extent to which it becomes integrated with existing lexical knowledge [1,2,3,4]
Such findings can be explained by complementary learning systems (CLS) accounts (e.g. [5,6]), which rest on the assumption that periods of consolidation are required for hippocampal memory traces to be reactivated and reach long-term neocortical systems
This finding is in line with previous studies that emphasize the role of offline consolidation in enhancing the integration of novel words into the mental lexicon (e.g. [3,14,15,21,56]) as well as dual memory system theories of word learning (e.g. [16])
Summary
An accumulation of behavioural and neuroimaging research suggests that sleep is one state that actively supports the consolidation of a newly encountered word, and the extent to which it becomes integrated with existing lexical knowledge [1,2,3,4] Such findings can be explained by complementary learning systems (CLS) accounts Dumay & Gaskell [3] administered a free recall task both immediately after training and 12 h later: participants were significantly better at recalling the novel words at the 12 h test, but only if they had slept Together, these results fit with computational theories that argue for a dual system of word learning to guard against ‘catastrophic interference’ (e.g. the CLS account; [6,16]). That sleep-associated delays in the emergence of lexical competition may depend upon the training conditions and the test of lexical competition that is used [11 –13]
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