A meta-analytic review is reported of empirical studies that investigate incubation effects on problem-solving. Although some researchers report increased solution rates after an incubation period, a period of time in which a problem is set aside prior to further attempts to solve, others have failed to find effects. The analysis examined contributions to incubation effect sizes of moderators such as problem type, presence of solution-relevant or misleading cues, and lengths of preparation and incubation periods. A positive incubation effect was identified, divergent thinking tasks benefiting more than linguistic and visual insight tasks from incubation. Longer preparation periods gave a greater incubation effect, while filling an incubation period with high cognitive demand tasks gave a smaller incubation effect. Surprisingly, low cognitive-demand tasks yielded a stronger incubation effect than rest during an incubation period when solving linguistic insight problems. The existence of multiple types of incubation effect provides evidence for differential invocation of knowledge-based versus strategic solution processes across different classes of problem, and suggests that the conditions under which incubation can be used as a practical technique for enhancing problem-solving must be designed with care.Keywords: Incubation, problem-solving, insight, meta-analysis Incubation and problem-solving 3 Does incubation enhance problem-solving? A meta-analytic review Anecdotal reports of the intellectual discovery processes of individuals hailed as geniuses (e.g. Wallas, 1926;Woodworth & Schlosberg, 1954; Ghiselin, 1985) share a common theme: a flash of insight pops unexpectedly into the mind of the individual after they have put an unsolved problem aside for a period of time, having failed in initial attempts to solve it. This temporary shift away from an unsolved problem that allows a solution seemingly to emerge as if from no additional effort is termed an 'incubation period' (Wallas, 1926). Its importance in current thinking and practice is illustrated by a yield of 5510 articles that mention the term 'Incubation', along with one of 'Creativity', 'Insight' or 'Problem', from a recent search of Google Scholar™, the search restricted to the years 1997 to 2007 and the subject areas of Social Sciences, Arts andHumanities. An additional 1970 articles were yielded by including Business, Administration andEconomics. Yet there are many conflicting accounts of incubation, some studies reporting strong effects (e.g., Smith & Blankenship, 1989), others failing to find any effect at all (Olton & Johnson, 1976). This paper aims to resolve the uncertainties surrounding the phenomenon by providing a statistical meta-analytic review of empirical studies of incubation. We suggest that it is only armed with the results of an integrative and quantitatively based review that progress in understanding the mechanisms that might underlie the phenomenon can be made.One theoretical reason for studying incubation is because it is cl...

Two experiments on performance on the traveling salesman problem (TSP) are reported. The TSP consists of finding the shortest path through a set of points, returning to the origin. It appears to be an intransigent mathematical problem, and heuristics have been developed to find approximate solutions. The first experiment used lO-point, the second, 20-point problems. The experiments tested the hypothesis that complexity of TSPs is a function of number of nonboundary points, not total number of points. Both experiments supported the hypothesis. The experiments provided information on the quality of subjects' solutions. Their solutions clustered close to the best known solutions, were an order of magnitude better than solutions produced by three well-known heuristics, and on average fell beyond the 99.9th percentile in the distribution of random solutions. The solution process appeared to be perceptually based.

The 9-dot problem is widely regarded as a difficult insight problem. The authors present a detailed information-processing model to explain its difficulty, based on maximization and progress-monitoring heuristics with lookahead. In Experiments 1 and 2, the model predicted performance for the 9-dot and related problems. Experiment 3 supported an extension of the model that accounts for insightful moves. Experiments 4 and 5 provided a critical test of model predictions versus those of previous accounts. On the basis of these findings, the authors claim that insight problem solving can be modeled within a means-ends analysis framework. Maximization and progress-monitoring heuristics are the source of problem difficulty, but also create the conditions necessary for insightful moves to be sought. Furthermore, they promote the discovery and retention of promising states that meet the progress-monitoring criterion and attenuate the problem space.

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This article reports 2 experiments that investigated performance on a novel insight problem, the 8-coin problem. The authors hypothesized that participants would make certain initial moves (strategic moves) that seemed to make progress according to the problem instructions but that nonetheless would guarantee failure to solve the problem. Experiment 1 manipulated the starting state of the problem and showed that overall solution rates were lower when such strategic moves were available. Experiment 2 showed that failure to capitalize on visual hints about the correct first move was also associated with the availability of strategic moves. The results are interpreted in terms of an information-processing framework previously applied to the 9-dot problem. The authors argue that in addition to the operation of inappropriate constraints, a full account of insight problem solving must incorporate a dynamic that steers solution-seeking activity toward the constraints.