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.
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.
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 and are monocular brightness flux signals. This equation can be thought of as the sum of the lengths of two vectors.
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