N-back

The n-back task is a continuous performance task that is commonly used as an assessment in cognitive neuroscience to measure a part of working memory and working memory capacity. The n-back was introduced by Wayne Kirchner in 1958.

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.

To clarify, the visual n-back test is similar to the classic memory game of "Concentration". However, instead of different items that are in a fixed location on the game board, there is only one item, that appears in different positions on the game board during each turn. "1-N" means that you have to remember the position of the item, one turn back. "2-N" means that you have to remember the position of the item two turns back, and so on.

For example, an auditory three-back test could consist of the experimenter reading the following list of letters to the test subject:

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.

The n-back task captures the active part of working memory. 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. To accomplish this task, the subject needs to both maintain and manipulate information in working memory.

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

The n-back task was developed by Wayne Kirchner for his research into short-term memory; he used it to assess age differences in memory tasks of "rapidly changing information".

There is some question about the construct validity of the n-back task. While the task has strong face validity and is now in widespread use as a measure of working memory in clinical and experimental settings, there are few studies which explore the convergent validity of the n-back task with other measures of working memory. Those studies have largely revealed weak or modest correlations between individuals' performance on the n-back task and performance on other standard, accepted assessments of working memory.

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