optical illusions

it is an optical illusion because if you stare on the cross(+)for about 5 - 20 seconds the colored dots will eventually disappear

actually, there are many such kinds pictures or paintings but they are not necessary animations. indeed, i think such kind of optical illusion is a bit hard to explain, it might be very natural or might be contributed to our vision or the mysterious pictures and i am wondering whether it is psychological. anyway, they are absolutely very amazing.

This is definitely an illusion. Even though it is a moving image, it is just the same thing over and over. Not only do the dots disappear, but there also seems to be a green dot swirling around, when that is really the missing space of the orange dot. It's just an illusion!