There are many ways of studying working memory. A classic example is the use of the n-back task. This is a type of serial working memory task wherein a person must hold a series of information in memory. The simplest version of the task, the 0-back, requires the person to respond every time they see the target stimulus. At 2-back, the task becomes very difficult. In the 2-back version below, for example, correct responses would be to the second and third Cs, because in both cases there was a C 2-letters prior.