Introduction to Lighting

Binocular Cues
 
Retinal Disparity
With the resurgence of 3D movies, this is the most commonly known technique in creating the illusion of depth. Your eyes are in different places and so receive different images. Our brains compare the differences and use that comparison as a reference for depth.
The image below is a stereogram. When viewed at the correct disatance, the imags will overlap and it will appear as one 3D image. A stereoscope will assist in viewing this image.
Convergence
To focus on an object that is close (such as the tip of your nose) our eyes need to rotate inwards, potentially until we are cross-eyed. For objects that are further away, our eyes are pointing almost straight forward.