Stare closely on the dancer and if you see her turning clockwise, then your right brain is more developed; if she is turning anti-clockwise, then you’re more developed on the left brain.
According to the experiment, 14% of the Americans can see the dancer is turning both left and right.
Additional info from Wikipedia:
In human beings, it is the left hemisphere that usually contains the specialized language areas. While this holds true for 97% of right-handed people, about 19% of left-handed people have their language areas in the right hemisphere and as many as 68% of them have some language abilities in both the left and the right hemisphere.
The two hemispheres are thought to contribute to the processing and understanding of language: the left hemisphere processes the linguistic meaning of prosody, while the right hemisphere processes the emotions conveyed by prosody. Studies of children have provided some fascinating information: If a child has damage to the left hemisphere, the child may develop language in the right hemisphere instead. The younger the child, the better the recovery. So, although the “natural” tendency is for language to develop on the left, our brains are capable of adapting to difficult circumstances, if the damage occurs early enough.