I’ve just been surprised and amused by an animated picture designed to identify the dominant side of your brain. (I’m not going to post the image here as I cannot find any copyright details for it. You can find it on many websites, including Gizmo Watch and Facebook.) The picture shows a silhouetted dancer spinning, but the direction of spin, clockwise or anticlockwise, depends on your brain.
When I first saw the picture she was spinning clockwise, but when I started to read the text she immediately started spinning anticlockwise! That makes perfect sense now, but it surprised me when it first happened; and it still amuses me every time I repeat it.
The explanation for the change in spin is quite simple: when I first look at the picture the right side of my brain tells me that she is spinning clockwise; but the left side of my brain (and your brain too) is responsible for reading, so when I start reading the left side kicks in and tells me that she is spinning anticlockwise; when I stop reading, she starts spinning clockwise again.
That’s astounding! Generally I see it anti-clockwise, but can force it at will to go clockwise by mental arithmetic (although, not anything that’s cached in tables like simple multiplication). I can also spot that it reverts to anti-clockwise when I’ve given myself a sum that’s reasonably tricky and my concentration wanders!