Contour rivalry

Contour rivalry is when two different pictures are presented to our eyes, but instead of seeing both at the same time, our brain switches back and forth between them. It is like having two toys you want to play with, but you can only play with one at a time. Our brain is the same way. It can only process one image at a time, so it has to choose which one to see.

For example, if you look at a picture of a vase and a picture of two faces, and both are drawn with lines that overlap, our brain may see one image as the dominant one (like the vase) and switch back and forth between the two pictures.

This happens because our brains are wired to recognize objects and shapes, but when there are two objects that are very similar, it has a hard time deciding which one is more important. It's like trying to play with two toys that look exactly the same - you have to focus on one to play with it properly.

So, when looking at two pictures with similar shapes, our brain tries to figure out which object is in front and which is in the background, making it switch back and forth between the two images. This is called contour rivalry.