cognitive fun!

Other interesting points about the Jaeggi, Buschkuehl et al. paper

Confounds are introduced into Jaeggi/Buschkuehl et al. study due to the use of German alphabets. Of course, the effect is arguable, and the same may hold true for any alphabet: there is an inherent familiarity with language-like sounds. The visual stimulus, on the other hand, looks reasonably novel. But then again, it's possible to guess that frequent video game players may have a faster rate of familiarization to these visual stimuli. Not that I would suspect a significant effect in the long run, but it does bring new considerations when tweaking the protocol.
Moreso than the semi-hypothetical video game player effect (there are some vaguely related reports in faint memory), the familiarity resulting from language sounds may reduce cognitive load during the task. But what auditory stimulus is truly novel? Suppose we use different instruments playing different chords. Some people will process major/minor chords faster than others. Suppose we use different timbres as differentiators. Just as Germans can process German sounds faster than non-Germans, strictly Western musicians could be slowed down if they had to tell koto and biwa notes.
Part of the next task is figuring out how to deliver this in an educational and interesting manner to the user, while stressing a possibly useful skill.