The lack of Aha! experience can be dependent on the problem difficulty.

Previous research on how problem-difficulty affects solution-types of insight-problems has yielded contradictory findings. Thus, we aimed to examine the impact of problem-difficulty on solution-types in both inter- and intra-problem-difficulty contexts. For this, we employed the original 8-coin, and 9-dot problems and four hinted-versions of those that were manipulated by using hints-to-remove-sources-of-difficulty to alter their difficulty level. Those manipulations were executed based on the assumptions of constraint-relaxation and chunk-decomposition as posited by representational change theory. The study involved a total of 165 participants who were tested in five groups (33 per se), with each group receiving an original or hinted problem. Following their correct solutions, problem-solvers classified their solution-types (insight or non-insight solutions) by whether they had an Aha!-experience during the solution. Across all groups, 56.1% of correctly solved insight problems were solved with Aha!-experience, based on participants' self-reports, implying that correct solutions should not be equated with insight. Subsequently, the solution-type rates were compared for both original problems (inter-problem-difficulty) and hinted versions of those at each difficulty level (intra-problem-difficulty). Inter-problem-difficulty comparisons demonstrated that the easier 8-coin problem was more likely to be solved with insight than the harder 9-dot problem. In contrast, intra-problem-difficulty comparisons revealed that harder problems were more likely to be solved with insight. These findings suggest that problem-difficulty should be considered in future studies of insight. Finally, separate analyses on the predictive values of the cognitive-affective-dimensions on solution-types revealed that, after adjusting for problem-difficulty, problem-solvers with higher suddenness scores in both problems exhibited a significantly higher probability of generating insight solutions.