The Psychology of Corner Radii

Neurological studies (Bar & Neta, 2006) demonstrate that human brains naturally perceive sharp, pointed objects as potential threats. The amygdala activates more strongly when viewing sharp geometric shapes compared to curved ones.

In interface design, a sharp 9px rectangle creates subconscious friction. A button with a 4px or 8px border radius softens the object, making it feel "safe" to touch. This biological wiring explains why operating systems routinely cycle back to heavy rounding (e.g., iOS 7, macOS Big Sur, Windows 11) to seem friendly and approachable.