This task examines both the ability to maintain information in working memory as well as to retrieve it. The subject is presented with a series of items, one at a time. In the 2-back version of the task, individuals indicate whether the current item in a sequence of items (forms, letters, digits) is the same as that mentioned 2 items previously. Thus, individuals must not only hold in mind the current item but also that one and two items back for comparison purposes. On each trial, information in working memory must be updated and a comparison must be performed.
Salthouse, T. A., & Pink, J. E. (2008). Why is working memory related to fluid intelligence? Psychonomic Bulletin & Review, 15, 364-371