Evidence for incubation effects in problem-solving is increasing, but the mechanisms that underlie incubation are unclear. An experiment tested two hypotheses about incubation: Spreading activation and opportunistic assimilation. Participants solved easy or difficult remote associates tasks without incubation period, or with an incubation period filled with high or low cognitive load tasks. A lexical decision task with cue and neutral words was given either before or after a second problem attempt. When solving difficult problems, the low-load incubation group benefitted more (...) from the presence of a cue than the high-load incubation group, and the opposite was found with easy problems. Neither incubation nor an initial problem attempt affected lexical decision times to cue words. The results favour opportunistic assimilation as an explanation of incubation effects. They also suggest a differential role for attentional allocation depending on problem difficulty, easy problems benefitting from focused attent.. (shrink)