Levels of brain activity may differ between introverts and extraverts. This has nothing to do with how clever a person is, it just reflects a general state of "activeness".
Levels of brain activity may be high in introverts, so they don't want to raise it further by attending wild parties. Extraverts may have lower brain activity, and like to raise it by seeking excitement.
We gave people two versions of the test, one that asked you to actively flip the cube and another that asked you to watch as the cube flipped passively by itself.
This experiment tests the hypothesis that because extraverts look for stimulation, they become bored easily. Having found one way of viewing the cube, extraverts tire quickly of that perspective, and make the image flip. We think extraverts will be faster than introverts at actively making the cube flip.
But in the version of the test where people were asked to watch as the cube flipped passively, introverts will be faster, because their level of brain activity is higher at rest.