What Is a Visual Key?

• A visual key is a point of reference in our visual fields that our brains use to interpret the raw data our eyes receive and turn it into useful information. With this information, we can then make informed estimates regarding such things as an object's size and distance from the viewer. This is one of the bases of depth perception.
  
  

How Does It Affect Our Sense of Space?

• Visual keys can affect our sense of space in several ways, depending on the key. For instance, we could focus on the corners and walls of a square room. We know that these walls are uniform in size and perfectly straight. But as the walls run further away from the eye, they seem to grow smaller and narrow down to a definable point. Our brains inherently know that such a narrowing of visual keys as they get further and further away is normal and can use the rate and degree to which they narrow to get an idea of how big the room is. Likewise, abnormal visual keys can fool our sense of space. Walls that don't perceptibly narrow, such as when the room really isn't square and actually gets larger as it travels away from the eye, fool the brain into thinking the room is very small.
  
  

Why?

• Our sense of space is affected by visual keys because of the intrinsic nature of the human eye. The eye perceives a flat two dimensional array of shapes, colors and images. In actual fact, what is being viewed is three dimensional. Our brains have need of visual keys so that they can translate this two dimensional panorama into full 3D.