Dual n-back



The n-back task is a Continuous Performance Task that is commonly used in neuroimaging to stimulate brain activity in test subjects. It was introduced by Kirchner in 1958.

The task
The subject is presented with a sequence of stimuli, and the task consists of indicating when the current stimulus matches the one from n steps earlier in the sequence. The load factor n can be adjusted to make the task more or less difficult.

For example, an auditory three-back test could consist of the experimenter reading the following list of letters to the test subject:
 * T L H C H S C C Q L C K L H C Q T R R K C H R

The subject is supposed to indicate when the letters marked in bold are read, because those correspond to the letters that were read three steps earlier.

Dual n-back
The dual-task n-back task was proposed by Susanne Jaeggi et al. in 2003. In this variation, two independent sequences are presented simultaneously, typically using different types of stimuli, such as one auditory and one visual.

In a 2008 research paper Jaeggi et al. claim that practicing a dual n-back task can increase fluid intelligence (Gf), as measured in several different standard tests. This resulted in some attention from popular media, including an article in Wired. The paper's methodology has been criticized by David Moody. He draws attention to the fact that different tests were used to evaluate the control and test groups. Due to the way in which the tests were administered, he also questions whether they were valid tests of fluid intelligence. For example, the progressive nature of the tests was undermined by severe time-restriction (10 minutes were allowed to complete a normally 45-minute test). In a subsequent study, Jaeggi et al addressed Moody's timing restriction criticism by noting that "that scores in timed versions of the APM are nicely predictive of scores in untimed versions (Frearson & Eysenck, 1986; Hamel & Schmittmann, 2006; Heron & Chown, 1967; Salthouse, 1993; Unsworth & Engle, 2005)".

The study was replicated in 2010 with results indicating that practising single n-back may be almost equal to dual n-back in increasing the score on tests measuring Gf.

There is a growing amount of evidence that cognitive training can have significant effects on the brain. In 2009, it was reported in Science that '14 hours of training over 5 weeks' on a variety of working memory related tasks (not including the n-back) led to measurable density changes for cortical dopamine neuroreceptors.

Software implementations
The dual n-back task can be played online, on most Java-enabled mobile phones (including Android and BlackBerry smartphones), the iPhone,  and Android. There is also a free, open-source application available for Mac OS, Linux, and Windows called Brain Workshop. The University of Bern sells the Jaeggi-Buschkuehl implementation in its Brain Twister suite.

The suite of working memory training tasks used in the study on dopamine receptor levels is available from Pearson Education.