Space refers to the visual field or surface in which things exist, move or can be placed. The space in which we live is organised in three dimensions. We perceive not only the spatial attributes (e.g., size, shape, direction) of various objects, but also the distance between the objects found in this space.

While the images of objects projected on to our retina are flat and two dimensional (left, right, up, down), we still perceive three dimensions in the space. This occurs due to our ability to transfer a two dimensional retinal vision into a three dimensional perception.

The process of viewing the world in three dimensions is called distance or depth perception. Three dimensional perception is a psychological process that depends on correct utilisation of certain monocular and binocular cues.

Depth perception is important in our daily life. For example, when we drive, we use depth to assess the distance of an approaching automobile, or when we decide to call a person walking down the street, we determine the loudness with which to call.