Abstract: Incubation effect refers to the phenomenon that when people are confronted with an unsolvable problem, they temporarily put it aside and switch to complete other irrelevant tasks instead, which is beneficial to the ultimate solution of the original problem. In recent years, researchers have conducted extensive studies on incubation effect of creative thinking and its influences, and put forward many theories to explain incubation effect. The representative theories include “selective forgetting theory”, “spreading activation and cue assimilation theory” and “unconscious work theory”. They explain the mechanism of incubation effect from different perspectives and predict different influences and phenomena respectively. For example, the attention-withdrawal theory supposes that the length of incubation will not influence the incubation effect. And the forgetting-fixation theory recommended a longer break to incubate. Furthermore, some factors are mentioned in many theories, such as the length of incubation and the length of preparation period. So the empirical researches about them can be explained by these related theories. While some factors are only mentioned by a few theories. For example, the function of beneficial cues can only be explained by the opportunistic assimilation theory. However, the research field of incubation effect has begun to combine with mind wandering and sleep. Many of the results of these studies are difficult to be well explained by the above theories, but should be explained in the light of the characteristics of mind wandering and sleep. Until now, related researches of mind wandering and sleep further shed light on the mechanism behind incubation effect. For example, mind wandering increases unconscious associate processing to serve creative problem-solving. Sleep, as a special long period of incubation, may promote problem solving through various mechanisms such as the reconstruction of memory representation and the reactivation of memory. But there is also conflicting evidence as to whether mind wandering and sleep promote the incubation effect. There are many studies that have failed to prove the effect of mind wandering and sleep on creative problem solving. The psychological processes underlying the incubation effect includes at least two cognitive components: the transformation of problem representation and the formation of remote associations. Different brain mechanisms are responsible for these two basic components. During the incubation period, memory systems are regulated by the dorsolateral prefrontal cortex to break the fixation caused by false assumptions. The cooperation of right frontal lobe, temporal lobe and parietal lobe was beneficial to assimilation of beneficial cues. The striatum-hippocampus-prefrontal lobe network continued to catalyze the reconstruction of representations during incubation period. Mind wandering promotes insight through the interaction of the medial temporal lobe, default network and executive network. The research on sleep can reflect the mechanism of long-term incubation in real life, and future research can further investigate the role of different sleep stages and their corresponding brain mechanisms. Future research needs to improve the ecological validity of relevant studies, promote the development of incubation theories, improve reproducibility, explore the positive factors that promote the incubation effect, and pay attention to the relationship between the incubation effect and emotion or other non-cognitive factors.

Key words: incubation effect, unconscious thought, creativity