3.
Psychology is still trying to explain the perception of the position of an object in space, along with its shape, size, and so on, and to understand the sensations of color.
James J. Gibson
4.
The heart of the problem is not so much how we see objects in depth, as how we see the constant layout of the world around us. Space, as such, empty space, is not visible, but surfaces are.
James J. Gibson