Answer to Question 1
For solving many problems, the chief obstacle is not the need to find a suitable strategy for positive transfer. Rather, it is to avoid obstacles resulting from negative transfer. Incubationputting the problem aside for a while without consciously thinking about itoffers one way in which to minimize negative transfer. It involves taking a pause from the stages of problem solving.
A recent meta-analysis of incubation research studies yielded complex findings. When people have more time to prepare to solve a problem, incubation periods are usually more fruitful. Likewise, being occupied with tasks that are highly cognitively demanding is detrimental to the effect of an incubation period. The effect of incubation furthermore depends on the kind of task, with performance on divergent-thinking tasks (in which something has to be produced) benefiting more than performance on linguistic tasks, for example. Incubation seems to help because people continue to process, below consciousness, information about a problem on which they are incubating at the same time that they are attending to other matters. Many times, when problem solvers have come to a point at which they cannot think of a strategy to solve a problem, they suffer from mental fixation. Incubation can help relieve the fixation and therefore foster the problem-solving process.
Answer to Question 2
Functional fixedness is the inability to realize that something known to have a particular use also may be used to perform other functions. Functional fixedness prevents us from solving new problems by using old tools in novel ways. Becoming free of functional fixedness is what first allowed people to use a reshaped coat hanger to get into a locked car. It is also what first allowed thieves to pick simple spring door locks with a credit card.
Problem Solving: Aha! Moments
Solving by elimination
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Differential Equation Word Problem