Piloting an ocean exploration ship or Martian research shuttle is serious business. Let’s hope the control panel is up to scratch. Two studs wide and angled at 45°, the ubiquitous “2x2 decorated slope” is a LEGO minifigure’s interface to the world. article 
This article is a beautiful and playful introduction to interface design and human cognition.
Diverse collection of LEGO interface bricks - co.uk
Differentiating inputs - co.uk
Also linked to another article on Gestalt Perception.