Normal brains process information synthetically (a.k.a. holistically.) This means they focus on the big picture – they don’t focus on the details. Or more precisely, they focus on the details but the amount of time they spend focusing on the details is minimal. They spend more time shifting their attention than they spend maintaining it. You can say they “glance over the details”. You cannot see the whole if you are focusing on the parts for too long – you will only see a lot of parts. You cannot see the forest if you are focusing on the trees for too long – you will only see a lot of trees. So a global thinker will see a circle where a local thinker won’t see a circle (e.g. UrWrong’s picture.)
When you focus on the big picture you lose the sight of the details and vice versa. When we look at UrWrong’s picture we see a circle. We don’t see its details, and hence, we don’t see the imperfections. If we switch out attention away from the big picture and towards the details, then yes, we would be able to see the imperfections, but this won’t make us abandon our earlier claim. If we did abandon the claim and if we adopted the attitude of spending disproportionately long time looking for imperfections then our understanding of circles would become so strict that most, if not all, of the shapes that we normally consider to be circles would no longer be seen as circles. That’s horribly counter-inuitive.