If you've felt disappointed at not being a genius who can draw a perfect circle, well, take solace: BrainDecoder explains the matter in detail, and it's not exactly your fault. The site starts by pointing out that we can recognize a perfect vs. imperfect circle pretty easily, and we have evolution to thank. The brain's visual cortex has evolved over time to help us distinguish the "subtlest differences" that could really matter, allowing us to, say, "avoid poisonous mushrooms but harvest edible ones." But BrainDecoder points out the ability to correct imperfections requires "completely different parts of the brain" tied to coordination and fine muscle control. And when it comes to the brain, it "prefers simplicity," like moving a single joint rather than several at the same time. In order to draw a perfect circle, though, the brain has to challenge this habit.
"During most arm movements, the shoulder is used as the handle and the elbow trails behind," explains Natalia Dounskaia, an associate professor of kinesiology. "This is similar to a whip: you actively move the handle and the entire leash moves passively." But the perfect freehand circle requires the shoulder and elbow to work together. "The brain needs to deal with many, many parameters," Dounskaia says. "It's a lot of additional work." Still, it is possible to draw the perfect circle by hand, as a one-time winner of the World Freehand Circle Drawing Championship (yes, there is such a thing) proves in this awesome video, which has been viewed 9.5 million times. Research shows artists tend to be better at drawing circles, perhaps because they are better at seeing and correcting errors as they work, but experts agree improvement does come with practice. Dig into the science more at BrainDecoder, or see how to cheat your way to a perfect one.