The incubation effect occurs when a period of rest or distraction from an unsolved problem leads to subsequent improvement in solving it. Anecdotes abound — Archimedes in his bath, Kekule dreaming of the benzene ring structure, Poincare's mathematical insights while boarding a bus — but experimental evidence has been harder to establish conclusively. Meta-analyses (Sio and Ormerod, 2009) suggest the effect is real but modest, and strongest for divergent thinking tasks.
Explanations
Several mechanisms have been proposed. Spreading activation continues unconsciously, gradually activating solution-relevant concepts. Forgetting of misleading fixation allows the problem solver to approach the problem from a fresh perspective after the break. Selective forgetting of inappropriate strategies weakens mental set. Opportunistic assimilation allows environmental stimuli encountered during incubation to trigger relevant associations.
Sleep may provide a particularly effective incubation period. Wagner et al. (2004) showed that participants who slept after working on a number reduction task were twice as likely to discover a hidden shortcut rule compared to participants who stayed awake for the same duration. Sleep-dependent memory consolidation may reorganize problem representations, facilitating the extraction of hidden regularities and the integration of distantly related information.