<p>The set is not always the one you suggest. There are many implementations that don't even involve letters, but use random shapes, numbers, spatial locations, or other stimuli.</p>

<p>In <a href="http://www.psy.unibe.ch/unibe/philhuman/psy/apn/content/e5616/e5621/e6314/e6333/files6334/Jaeggi_et_al2007_ger.pdf">Jaeggi et al., 2007</a>, they used spatial locations for the visual task, and</p>

<blockquote>
  <p>The auditory material consisted of eight German consonants (c, g, h, k, p, q, t, and w) spoken in a female voice and <strong>selected on the basis of their distinctiveness</strong>.</p>
</blockquote>

<p>(emphasis mine).</p>

<p>In <a href="http://www.jneurosci.org/content/30/9/3297.short">Takeuchi et al. 2010</a>, they used numbers and locations:</p>

<blockquote>
  <p>“Dual” N-back task. In this task, the number stimuli consisted of numbers, 1 to 4, presented in a random sequence in one of four places on a line. </p>
</blockquote>

CC BY-SA 3.0
2012-02-11T09:28:36.183Z
2012-02-11T09:28:36.183Z
Ofri Raviv
<p>Every implementation of <a href="http://en.wikipedia.org/wiki/N-back" rel="nofollow">dual n-back</a> that I've ever seen uses the set of letters 'C', 'H', 'K', 'L', 'Q', 'S', 'R' and 'T'.</p>

<p>Why is that?</p>

CC BY-SA 3.0
2012-02-10T22:49:04.373Z
Interesting. Might be to reduce ambiguity, those letters are mostly visually and audibly distinct as opposed to making a test of C D B G P or O G C Q D
Zelda
CC BY-SA 3.0
2012-02-11T00:16:54.473Z
I don't know that it *always* has to use those letters. (see www.brainboffin.com; also, a quick lit search shows it's also been done with numbers and Mandarin phonemes). I suspect it's partly to do with the phonetic properties of the sounds, as Ben Brocka suggests, and partly because the dual n-back has mostly been run by a single lab (Jaeggi). It's easier for them to consistently use the same experimental setup, and increases their chances of reproducing the effect.
Jeff
<intelligence><memory>
Why do dual N-back games use certain letters?
ʞɔıu
# Why do dual N-back games use certain letters?

(Asked by: username_0 on 2012-02-10)

Every implementation of [dual n-back](http://en.wikipedia.org/wiki/N-back) that I've ever seen uses the set of letters 'C', 'H', 'K', 'L', 'Q', 'S', 'R' and 'T'.

Why is that?

**Tags:** intelligence, memory

> **Comments:**
> **username_1**: Interesting. Might be to reduce ambiguity, those letters are mostly visually and audibly distinct as opposed to making a test of C D B G P or O G C Q D  
> **username_2**: I don't know that it *always* has to use those letters. (see www.brainboffin.com; also, a quick lit search shows it's also been done with numbers and Mandarin phonemes). I suspect it's partly to do with the phonetic properties of the sounds, as Ben Brocka suggests, and partly because the dual n-back has mostly been run by a single lab (Jaeggi). It's easier for them to consistently use the same experimental setup, and increases their chances of reproducing the effect.  

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## 1 answers

### Answer by username_3 on 2012-02-11. Score: 5 | Accepted answer

The set is not always the one you suggest. There are many implementations that don't even involve letters, but use random shapes, numbers, spatial locations, or other stimuli.

In [Jaeggi et al., 2007](http://www.psy.unibe.ch/unibe/philhuman/psy/apn/content/e5616/e5621/e6314/e6333/files6334/Jaeggi_et_al2007_ger.pdf), they used spatial locations for the visual task, and

> The auditory material consisted of eight German consonants (c, g, h, k, p, q, t, and w) spoken in a female voice and **selected on the basis of their distinctiveness**.

(emphasis mine).

In [Takeuchi et al. 2010](http://www.jneurosci.org/content/30/9/3297.short), they used numbers and locations:

> “Dual” N-back task. In this task, the number stimuli consisted of numbers, 1 to 4, presented in a random sequence in one of four places on a line.


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