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. 2017 Sep 7;8:1533.
doi: 10.3389/fpsyg.2017.01533. eCollection 2017.

Effects of Sleep on Word Pair Memory in Children - Separating Item and Source Memory Aspects

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Free PMC article

Effects of Sleep on Word Pair Memory in Children - Separating Item and Source Memory Aspects

Jing-Yi Wang et al. Front Psychol. .
Free PMC article

Abstract

Word paired-associate learning is a well-established task to demonstrate sleep-dependent memory consolidation in adults as well as children. Sleep has also been proposed to benefit episodic features of memory, i.e., a memory for an event (item) bound into the spatiotemporal context it has been experienced in (source). We aimed to explore if sleep enhances word pair memory in children by strengthening the episodic features of the memory, in particular. Sixty-one children (8-12 years) studied two lists of word pairs with 1 h in between. Retrieval testing comprised cued recall of the target word of each word pair (item memory) and recalling in which list the word pair had appeared in (source memory). Retrieval was tested either after 1 h (short retention interval) or after 11 h, with this long retention interval covering either nocturnal sleep or daytime wakefulness. Compared with the wake interval, sleep enhanced separate recall of both word pairs and the lists per se, while recall of the combination of the word pair and the list it had appeared in remained unaffected by sleep. An additional comparison with adult controls (n = 37) suggested that item-source bound memory (combined recall of word pair and list) is generally diminished in children. Our results argue against the view that the sleep-induced enhancement in paired-associate learning in children is a consequence of sleep specifically enhancing the episodic features of the memory representation. On the contrary, sleep in children might strengthen item and source representations in isolation, while leaving the episodic memory representations (item-source binding) unaffected.

Keywords: child development; declarative memory; electroencephalography; episodic memory; memory consolidation; sleep.

Figures

FIGURE 1
FIGURE 1
Experimental design and memory dynamics in children. (A) The Encoding phase of the experiment consisted of learning two lists of word pairs, each studied once 1 h apart. The duration of the retention interval was either 1 h (Pre-sleep condition) or 11 h with the latter including either a night of sleep (Sleep condition) or daytime wakefulness (Wake condition). In the retrieval phase cued recall was tested for each word pair followed by a recall of the list (forced choice between List 1 and 2) in which the word pair had appeared. Each recall trial was categorized according to the correctness of the associated target word (WP) or the associated list (L) as depicted in the grayed area of Venn diagrams next to the bar graphs. (B–G) Children’s mean (± SEM) cued recall performance for the Pre-sleep (gray bars), Sleep (black) and Wake (white) conditions for (B) correctly recalled word pairs, (C) correctly recalled lists, (D) trials with both correctly recalled word pairs and lists, (E) trials with correctly recalled word pairs or lists or both, (F) trials with correctly recalled word pairs but incorrect list recall, and (G) trials with correct list recall but incorrect word pair recall. Recall is expressed as the difference from immediate recall of word pairs during the encoding phase. p < 0.05, ∗∗p < 0.01, for pairwise comparisons between retention conditions.
FIGURE 2
FIGURE 2
Comparison of recall performance between children (white bars) and adults (black) for the 1-h Pre-sleep condition (left bars) and 11-h Sleep conditions (right bars) for (A) immediate recall of word pairs during the encoding phase (B) delayed recall of word pairs (expressed as the difference from immediate recall as in A), and for subgroups of trials (C) with combined correct word pair and list recall and (D) with correct word pair but incorrect list recall. Recall is expressed as the percentage of the total number of word pairs presented at the encoding phase (40 in children, 80 in adults). Note, recall in (C,D) is not adjusted to the individual’s immediate recall during the encoding phase. Gray area in the Venn diagrams next to the bar graphs depicts the trial category as in Figure 1 with respect to correctness of the delayed word pair (WP) or associated list (L) recall. p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001 for pairwise comparisons.

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