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Abstract:
Objectives: Sleep has been shown to benefit a range of cognitive functions, including memory consolidation. While there is ample evidence for a quantitative effect of sleep on learned material, there is an ongoing debate whether sleep also promotes qualitative changes in how new material is represented. Insight problems often require reorganization of the problem representation or problem space in order to be solved and thus have already been employed to explore the role of sleep in qualitatively restructuring memory content. While some results suggest that sleep can help gain sudden insight e.g. into hidden rules underlying previously learned material, other studies emphasize the role of incubation time for solving insight problems. In the current study, we investigate the effect of both incubation time and sleep on solving different insight problem tasks. Materials: In a 3h daytime nap vs. wake design, four groups of participants (total n=72) worked on various problem solving tasks, including classical as well as perceptual insight problems, anagrams, word and logic riddles. Participants attempted to solve the problems during a short initial 'encoding' phase and a longer second 'retest' phase. While two groups experienced a 3h 'incubation' interval between encoding and retest, which was either spent asleep or awake, the other groups spent an equal interval asleep or awake before the encoding phase, which was then immediately followed by the retest. Results: We find that a time interval between encoding and retest, regardless of whether this interval is spent awake or asleep, can increase solution rates or solution times in both reasoning and perceptual insight problems. Conclusions: We conclude that for the materials and time-window tested, there is no specific effect of sleep on the reorganization of encoded material leading to insight problem solving. However, it seems that for certain problems, the restructuring of the problem can take place during the time between forming the initial representation and later attempts at solving the task. This incubation effect is in line with insight models that assume that initial neuronal activation patterns must decay before the solution can emerge.
