Academic journal article Memory & Cognition

Sleep on It, but Only If It Is Difficult: Effects of Sleep on Problem Solving

Academic journal article Memory & Cognition

Sleep on It, but Only If It Is Difficult: Effects of Sleep on Problem Solving

Article excerpt

Published online: 6 October 2012

© Psychonomic Society, Inc. 2012

Abstract Previous research has shown that performance on problem solving improves over a period of sleep, as compared with wakefulness. However, these studies have not determined whether sleep is beneficial for problem solving or whether sleep merely mitigates against interference due to an interruption to solution attempts. Sleep-dependent improvements have been described in terms of spreading activation, which raises the prediction that an effect of sleep should be greater for problems requiring a broader solution search. We presented participants with a set of remote-associate tasks that varied in difficulty as a function of the strength of the stimuli-answer associations. After a period of sleep, wake, or no delay, participants reattempted previously unsolved problems. The sleep group solved a greater number of difficult problems than did the other groups, but no difference was found for easy problems. We conclude that sleep facilitates problem solving, most likely via spreading activation, but this has its primary effect for harder problems.

Keywords Insight * Problem solving * Sleep * Learning * Task complexity

Many scientific discoveries and masterpieces in art and literature were inspired by dreams, suggesting the importance of sleep in solution discovery (Cartwright, 1974). One famous example, for instance, is Loewi's discovery of the chemical transmission of nerve impulses in his dream (Stickgold & Walker, 2004). Recent empirical studies have supported the anecdotal evidence that sleep has a profound facilitatory effect across a range of different types of problems (Cai, Mednick, Harrison, Kanady, & Mednick, 2009; Wagner, Gais, Haider, Verleger, & Born, 2004). Furthermore, Kuriyama, Stickgold, and Walker (2004) discovered that sleep has a differential effect for easier versus harder motor skill tasks: Sleep was most beneficial for greater complexity. However, it is unclear whether such distinctions in difficulty apply to more complex cognitive tasks such as problem solving. In this study, we examined the effect of sleep in terms of how task characteristics govern the effect of sleep on problem solving.

A growing body of work suggests that sleep has an effect on associations among concepts in processing and memory (e.g., Cai et al., 2009), facilitating restructuring of information (Payne, 2011; Payne et al., 2009; Stickgold, Scott, Rittenhouse, & Hobson, 1999), which is a key aspect of problem solving (e.g., Ohlsson, 1992, 2011). Using the DRM paradigm, Payne et al. reported sleep-dependent consolidation of false memories, which has been interpreted in terms of activation spreading from representations of presented words to related concepts during sleep. Stickgold et al. tested the effects of semantic priming among weakly and strongly related prime-target pairs when participants were awakened from different stages of sleep. Stickgold et al. found that on waking from rapid eye movement (REM) sleep, weakly related word pairs produced more semantic priming than did strongly related pairs, as compared with waking from non-rapid eye movement sleep or being awake. However, these three groups did not differ in the strength of priming between strongly related words. This result was interpreted in terms of spreading activation among concepts facilitated by sleep, indicating that, during REM sleep, activation of the presented stimuli spread widely to more remotely associated concepts, rather than activation being confined only to close associates.

Spreading activation has been proposed as one of the primary cognitive mechanisms underlying insight (Ohlsson, 1992, 2011) and has been discussed in particular in relation to solving problems such as remote-associate tests (RATs). RAT problems require finding a word that is related to three given words (e.g., lick, sprinkle, mine; answer: salt). For RAT problems, activation is conceived to pass across a semantic associative network (Collins & Loftus, 1975) between stimulus and target words, with intermediary associates also becoming activated (Mednick, 1962), and when activation of the target word exceeds a threshold, it becomes available as a solution to the problem. …

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