Why Rounded Corners are Easier on the Eyes
Anyone can appreciate the aesthetic beauty of rounded corners, but not everyone can explain where exactly that beauty comes from. The answer to that is literally in your eye.
Some experts say that rectangles with rounded corners are easier on the eyes than a rectangle with sharp edges because they take less cognitive effort to visually process.
The fovea is fastest at processing circles. Processing edges involve more “neuronal image tools” in the brain [1]. Thus, rectangles with rounded corners are easier process because they look closer to a circle than a regular rectangle.
Scientific research done on corners by the Barrow Neurological Institute found that the “perceived salience of a corner varies linearly with the angle of the corner. Sharp angles generated stronger illusory salience than shallow angles” [2]. In other words, the sharper the corner, the brighter it seems. And the brighter a corner appears, the more it’ll affect visual processing.
http://uxmovement.com/thinking/why-rounded-corners-are-easier-on-the-eyes/