When n equals 2 or more, it is not enough to simply keep a representation of recently presented items in mind; the working memory buffer also needs to be updated continuously to keep track of what the current stimulus must be compared to.
[5] In the dual-task paradigm, two independent sequences are presented simultaneously, typically using different modalities of stimuli, such as one auditory and one visual.
Several smart phone apps and online implementations of the dual n-back task exist.
[7][8] There are two main hypotheses for this weak correlation between the n-back task and other working memory assessments.
[8] A 2008 research paper claimed that practicing a dual n-back task can increase fluid intelligence (Gf), as measured in several different standard tests.
[13] Two studies published in 2012 failed to reproduce the effect of dual n-back training on fluid intelligence.
[14][15] In 2014, a meta-analysis of twenty studies showed that n-back training has small but significant effect on Gf and improve it on average for an equivalent of 3–4 points of IQ.
[17] A more recent and extended meta-analysis in January 2017[18] also found that n-back training produces a medium improvement in unrelated n-back training tasks, but a small improvement in unrelated working memory (WM) tasks: The present meta-analysis on the efficacy of n-back training shows medium transfer effects to untrained versions of the trained n-back tasks and small transfer effects to other WM tasks, cognitive control, and Gf [fluid intelligence].
[21] Tutoring companies and psychologists also utilize the task to improve the focus of individuals with ADHD[21] and to rehabilitate sufferers of traumatic brain injury;[22] experiments have found evidence that practice with the task helps these individuals focus for up to eight months following training.
Researchers from the University of Oslo published results of the meta-analytical review analyzing various studies on memory training techniques (including n-back) and contentiously concluded that "training programs give only near-transfer effects, and there is no convincing evidence that even such near-transfer effects are durable.