way to attach a candle to the wall to light the room. The solution requires the participants to empty the box of tacks, set the candle inside the box, tack the box to the wall, and light the candle with the matches. Spatial ability The second type of insight problem requires spatial ability to solve, like the "Nine-dot problem". The famous "Nine-dot problem" requires participants to draw four lines, through nine dots, without picking their pencil up. Using verbal ability The third and final type of problem requires verbal ability to solve, like the Remote Associates Test (RAT). In the RAT, individuals must think of a word that connects three, seemingly unrelated, words. RAT are often used in experiments, because they can be solved both with and without insight. Specific results Versus non-insight problems Two clusters of problems, those solvable by insight and those not requiring insight to solve, have been observed. An individual’s cognitive flexibility, fluency, and vocabulary ability are predictive of performance on insight problems, but not on non-insight problems. In contrast, fluid intelligence is mildly predictive of performance on non-insight problems, but not on insight problems. More recent research suggests that rather than insight versus search, that the subjective feeling of insight varies, with some solutions experienced with a stronger feeling of Aha than others. Emotion People in a better mood are more likely to solve problems using insight. Research demonstrated that self-reported positive affect of participants uniquely increased insight before and during the solving of a problem, as indicated by differing brain activity patterns. People experiencing anxiety showed the opposite effect, and solved fewer problems by insight. Emotion can also be considered in terms of the insight experience and whether this is a positive Aha or negative Uh-oh moment. Research demonstrate that in order to have insights it is important to have a good degree of access to one's own emotions and sensations, that can cause insights. To the degree that individuals have limited introspective access to these underlying causes, they have only limited control over these processes as well. Incubation Using a geometric and spatial insight problem, it was found that providing participants with breaks improved their performance as compared to participants who did not receive a break. However, the length of incubation between problems did not matter. Thus, participants' performance on insight problems improved just as much with a short break (4 minutes) as