Abstract
Vocabulary is crucial for an array of life outcomes and is frequently impaired in developmental disorders. Notably, 'poor comprehenders' (children with reading comprehension deficits but intact word reading) often have vocabulary deficits, but underlying mechanisms remain unclear. Prior research suggests intact encoding but difficulties consolidating new word knowledge. We test the hypothesis that poor comprehenders' sleep-associated vocabulary consolidation is compromised by their impoverished lexical-semantic knowledge. Memory for new words was tracked across wake and sleep to assess encoding and consolidation in 8-to-12-year-old good and poor comprehenders. Each child participated in two sets of sessions, one beginning in the morning (AM-encoding) and the other in the evening (PM-encoding). In each case, they were taught 12 words and were trained on a spatial memory task. Memory was assessed immediately, 12- and 24-hr later via stem-completion, picture-naming, and definition tasks to probe different aspects of word knowledge. Long-term retention was assessed 1-2months later. Recall of word-forms improved over sleep and postsleep wake, as measured in both stem-completion and picture-naming tasks. Counter to hypotheses, deficits for poor comprehenders were not observed in consolidation but instead were seen across measures and throughout testing, suggesting a deficit from encoding. Variability in vocabulary knowledge across the whole sample predicted sleep-associated consolidation, but only when words were learned early in the day and not when sleep followed soon after learning. Poor comprehenders showed weaker memory for new words than good comprehenders, but sleep-associated consolidation benefits were comparable between groups. Sleeping soon after learning had long-lasting benefits for memory and may be especially beneficial for children with weaker vocabulary. These results provide new insights into the breadth of poor comprehenders' vocabulary weaknesses, and ways in which learning might be better timed to remediate vocabulary difficulties.
Highlights
Good vocabulary knowledge is a key contributor to comprehension success (Perfetti, 2007) and – in turn – successful comprehension permits the acquisition of new word knowledge (Verhoeven, van Leeuwe, & Vermeer, 2011)
An exploratory analysis using expressive vocabulary knowledge as a predictor of word-form recall suggested that sleep soon after learning may be especially beneficial for children with weak vocabulary knowledge: existing vocabulary did not predict changes in memory during the first 12-hr of learning, whereas children with poorer existing knowledge were less able to benefit from sleep during the 12–24hr period. It did not appear as if children with weaker vocabulary ability had forgotten more items during the course of the day (Figure 6), an explanation considered by Walker et al (2020). We propose that these differences reflect the multiple ways in which new information may be ‘tagged’ for memory consolidation (Stickgold & Walker, 2013): all children may benefit from the saliency of learning information immediately before bed, whereas superior vocabulary knowledge affords more robust connections to prior knowledge that can facilitate consolidation regardless of delay
This study showed that children with reading comprehension difficulties have a lower capacity for vocabulary learning than children with good comprehension and that this relative impairment is apparent even when new vocabulary is taught directly
Summary
Good vocabulary knowledge is a key contributor to comprehension success (Perfetti, 2007) and – in turn – successful comprehension permits the acquisition of new word knowledge (Verhoeven, van Leeuwe, & Vermeer, 2011). To understand individual differences in vocabulary acquisition, we must consider both how to successfully encode a new word representation in memory, and the factors that enable consolidation of this initial representation into longer-term vocabulary. Understanding variability in both processes is critical for better targeting robust and long-lasting vocabulary instruction. Sleeping soon after learning had long-lasting benefits for memory and may be especially beneficial for children with weaker vocabulary. These results provide new insights into the breadth of poor comprehenders’ vocabulary weaknesses, and ways in which learning might be better timed to remediate vocabulary difficulties.
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