The object of dual n-back training is to increase the number of items you can hold in mind at one time, known as your "working memory". This number varies naturally from person to person, the limit being about seven or eight items. It should make sense that the more information you can hold in short-term memory, the more complex the problems you can solve (and thus the smarter you are).
This dual n-back training game strengthens your working memory by forcing you to remember a sequence of n-back items that increases in length as the game gets harder. The better you get at the game, the further back in the sequence you must remember. The "dual" (meaning twice) portion of dual n-back refers to the fact that you must recall a sequence of sounds and a sequence of images at the same time.Researchers found that persons who practiced dual n-back training showed a 30 percent improvement in their working memory. (1)