This paper explores the effect of different types of incubation task (visual, numerical and verbal) with various levels of attentional focus and cognitive effort (non-demanding, low-demanding and high-demanding) on the resolution of insight problems. The most effective was found to be the low-demanding task (regardless of its nature), which although requiring attentional focus, leaves resources available for the unconscious analytical restructuring process, obtaining a high percentage of success in solving the problem shortly after completion of the incubation task. Overall findings (...) support the hypothesis of Unconscious Analytic Thought (UAT), according to which the restructuring required in insight problem solving implies a covert thinking process that includes a relevant, analytic and goal-oriented search. The findings are discussed in the light of UAT and are compared with the main theories of insight in problem solving. (shrink)