Binocular summation

Binocular summation refers to the improved visual performance of binocular vision compared to that of monocular vision. The most vital benefit of binocular vision is stereopsis or depth perception, however binocular summation does afford some subtle advantages as well. By combining the information received in each eye, binocular summation can improve visual acuity, contrast sensitivity, flicker perception, and brightness perception. Though binocular summation generally enhances binocular vision, it can worsen binocular vision relative to monocular vision under certain conditions. Binocular summation decreases with age and when large interocular differences are present.
Visual Improvements.
Some of the ways in which binocular summation improves binocular visual performance are
A practical measure of binocularity is the binocular summation ratio BSR, which is the ratio of binocular contrast sensitivity to the contrast sensitivity of the better eye. 
Models for binocular brightness.
One might expect the inputs from each eye to simply add together, and that the perceived brightness with two eyes is twice that of a single eye. However, the perceived brightness with two eyes is only slightly higher compared to a single eye. If one eye sees a bright scene, the perceived brightness will actually decrease if the other eye is presented with a dim light. This counterintuitive phenomenon is known as Fechner's Paradox. Several different models have been proposed to explain how the inputs from each eye are combined.
The renowned physicist Erwin Schrödinger, known for his contributions to quantum theory, had a fascination for psychology and he explored topics related to color perception. Schrödinger (1926) put forth an equation for binocular brightness and contrast combination where each monocular input is weighted by the ratio of the signal strength from that eye to the sum of the signal from both eyes. The inputs formula_2 and formula_2 are monocular brightness flux signals. This equation can be thought of as the sum of the lengths of two vectors.
MacLeod (1972) expanded upon Schrödinger's work by proposing the following formula for the signal strength of a neural signal formula_5 in terms of internal noise formula_6, luminance difference across the contour formula_7, and threshold luminance difference formula_8.
Process.
It is still uncertain exactly how this process is performed by the brain and remains an active area of research. The mechanism can be explained by some combination of probability summation, neural summation, and effects due to binocular-monocular differences in pupil size, accommodation, fixation, and rivalry. Probability summation comes from the principle that there is a greater chance of detecting a visual stimulus with two eyes than with one eye.
There are five possible results when the input stimuli are summed together. These are
Binocular Fusion.
Both motor fusion and sensory fusion mechanisms are used to combine the two images into a single perceived image. Motor fusion describes the vergence eye movements that rotate the eyes about the vertical axis. Sensory fusion is the psychological process of the visual system that creates a single image perceived by the brain.