I wonder why it biases in one direction? I could see this working like one of those 2-in-1 images or the rotating ballerina, where the picture you see, or the direction she's rotating changes depending on how you look at it, but I couldn't make the spirals go a different direction.
Our visual systems are an amazing thing.
My guess is that the bias is caused by the black shapes. You can see that each black shape is closer to its bigger "parent" on the left on the next row out than it is to its bigger parent on its right. Also the connection to the parent on the left is through dark blue, and the connection to the parent on the right is through light blue. That's enough to give a bias.