Insight denotes a mental restructuring that leads to a sudden gain of explicit knowledge allowing qualitatively changed behaviour. Anecdotal reports on scientific discovery suggest that pivotal insights can be gained through sleep. Sleep consolidates recent memories and, concomitantly, could allow insight by changing their representational structure. Here we show a facilitating role of sleep in a process of insight. Subjects performed a cognitive task requiring the learning of stimulus-response sequences, in which they improved gradually by increasing response speed across task blocks. However, they could also improve abruptly after gaining insight into a hidden abstract rule underlying all sequences. Initial training establishing a task representation was followed by 8 h of nocturnal sleep, nocturnal wakefulness, or daytime wakefulness. At subsequent retesting, more than twice as many subjects gained insight into the hidden rule after sleep as after wakefulness, regardless of time of day. Sleep did not enhance insight in the absence of initial training. A characteristic antecedent of sleep-related insight was revealed in a slowing of reaction times across sleep. We conclude that sleep, by restructuring new memory representations, facilitates extraction of explicit knowledge and insightful behaviour.

Insight problem solving is characterized by impasses, states of mind in which the thinker does not know what to do next. The authors hypothesized that impasses are broken by changing the problem representation, and 2 hypothetical mechanisms for representational change are described: the relaxation of constraints on the solution and the decomposition of perceptual chunks. These 2 mechanisms generate specific predictions about the relative difficulty of individual problems and about differential transfer effects. The predictions were tested in 4 experiments using matchstick arithmetic problems. The results were consistent with the predictions. Representational change is a more powerful explanation for insight than alternative hypotheses, if the hypothesized change processes are specified in detail. Overcoming impasses in insight is a special case of the general need to override the imperatives of past experience in the face of novel conditions. Experience is both a help and a hindrance. On the one hand, human beings have no choice but to consider each new situation, task, or problem in light of past experience. There is no other resource for understanding the present and anticipating the future. On the other hand, life is complex, and there is no guarantee that tomorrow will be like yesterday. Past experience is necessarily misleading part of the time. Problem solving often unfolds in a way that reflects the need to overcome the imperatives of past experience. The thinker begins by exploring the approaches to the problem

Two experiments tested H. Haider and P. A. Frensch's (1996) information-reduction hypothesis that people learn, with practice, to distinguish between task-relevant and task-redundant information and to limit their processing to task-relevant information. Participants verified alphabetic strings (e.g., "E [4] J K L") containing task-relevant and task-redundant information. In Experiment 1, the positioning of task-relevant information within the strings and the consistency of positioning were manipulated. Degree of information reduction as reflected in reduced reaction times was not affected by the positioning of the relevant information and was only slightly affected by consistency of the positioning. In Experiment 2, eye movements were recorded. Results suggest that task-redundant information is ignored at a perceptual rather than a conceptual level of processing. Thus, existing theories of skill acquisition should include mechanisms that capture the practice-related increase in the selective use of information.

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