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That's a well-done version of an old visual phenomenon.  To give proper 
credit, this was designed by Nobuyuki Kayahara in 2003, and you can see the 
original here: http://www.procreo.jp/labo/silhouette.swf   It has nothing 
to do with right-brain / left-brain differences; somehow that erroneous 
"explanation" got attached to this and became a viral e-mail in 2007.

Some experiments you can try:

(1)  Look at a mirror image of the illusion (either a software reversal, or 
in an actual mirror).  Does the mirror image spin the same way, or 
opposite?  Does it matter whether you use a horizontal or vertical mirror 
image?
(2)  Run two identical copies of the illusion side-by-side.  Do they spin, 
and change direction, in synchrony?  What if they're mirror images?
(3)  Look at it with a dark filter over one eye,and then the other.  Does 
that affect the direction of spin?  (This would now be the Pulfrich effect, 
which Eric Siegel referenced.)

For more explanation, and the chance to try two more experiments, check out 
Michael Bach's interactive version: http://www.procreo.jp/labo/silhouette.swf

-Richard

At 05:50 AM 11/11/2008, you wrote:

>ISEN-ASTC-L is a service of the Association of Science-Technology Centers
>Incorporated, a worldwide network of science museums and related institutions.
>*****************************************************************************
>
>Like the one posted a few months ago where the b&w picture suddenly
>became color - this one has me stumped.....any answers?
>
>http://tinyurl.com/33va3f
>
>Just because it is described as a left/right brain artifact, knowing
>that does nothing to help me understand why!
>
>
>
>
>
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