I wanted to bring into this separate post a comment from blog reader Erik, made below. You don't have to own an iPhone and pay six bucks to do the dual-n-back tests. Erik's comment:
Hey. I'd just add that there are some accurate dual-n-back implementations on the web. Ours is open source, and it's here: dual n back implementation . It follows the protocol very closely, and it even got a thumbs up from the researchers.