In order to determine if a person's left or right hemisphere is more important for their language production, physicians use things like the WADA test, in which a barbiturate is injected into one hemisphere to temporarily shut it down, allowing the physician to see what each hemisphere can do on its own. This is obviously a very invasive test (and not perfect at that). If it were possible to instead figure out whether someone relied more on their left or right hemisphere by having them look at a spinning figure or answer a few questions, that would obviously be preferable ... but it doesn't work.

The Truth About The Left Brain / Right Brain Relationship : 13.7: Cosmos And Culture : NPR Wednesday, December 4, 2013 @ 9:47pm