Explain the role of binocular cues …

The monocular cues of depth perception induce depth in objects when viewed through a single eye. They are also known as pictorial cues as they are used by artists to induce depth in two-dimensional paintings. Important monocular cues are relative size and height, interposition, linear and aerial perspective, light and shade, texture gradient, and motion parallax.

The binocular cues of depth perception are provided by both the eyes in three-dimensional spaces. Their role in the perception of depth is as follows:

(i) Retinal or Binocular disparity: It occurs when the two eyes have different locations in the head and are separated horizontally with a difference of 6.5 centimetres. The difference in the images formed by the eyes is due to the retinal disparity. Large retinal disparity means a close object and small retinal disparity means a distant object.

(ii) Convergence: When the eyes converge inward to bring the image on the fovea of each eye, a group of muscles sends messages to the brain which are interpreted as cues to the perception of depth. The degree of convergence decreases with an increase in distance of the object.

(iii) Accommodation: It is the process through which the image is focussed on the retina with the help of a ciliary muscle. These muscles change the thickness of the eye lens. The degree of contraction of the muscles provides a cue to distance. The muscles relax when the object is distant and contract when the object is near.