One of the tests in Brain Age is the classic Stroop Test, rendered for the small handheld device.
Stroop tests were named of course after Stroop, way back in 1935 and his doctoral dissertation.
In this test you have to inhibit your expectation. For example, I see the word 'Yellow' but the font is green. Typically you are asked to choose whether the color/text association is correct or not.
Introducing 'speed' into the measurement makes it a more challenging brain exercise.
The Univ. of Michigan has a good discussion of Stroop, directed attention, and the effects on the brain for any budding game developers or just the curious.