5.8 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Binocular vision | 3/6 | https://en.wikipedia.org/wiki/Binocular_vision | reference | science, encyclopedia | 2026-05-05T15:53:38.467964+00:00 | kb-cron |
=== Predictor of binocular depth perception === Whether animals possess the ability for binocular depth perception is not self-evident. First, eye position is a predictor of binocular depth perception. Binocular depth perception requires overlap between the visual fields of both eyes, but this is not a sufficient condition. For example, some birds are known to have a small overlap of visual fields when looking straight ahead, but this is used to steer effectively during rapid flight movements based on motion vision. This illustrates that having an animal's eyes at the front does not automatically mean it possesses binocular depth perception. The type of eye movements is also a predictor of binocular depth perception, but it is also not a sufficient condition. Under prevalence of stereopsis in animals it is indicated in which animals stereopsis has been found.
=== Eye position ===
Some animals – usually prey – have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. Examples include rabbits, buffalo, and antelopes. In such animals, the eyes often move independently to increase the field of view. Even without moving their eyes, some birds have a 360-degree field of view. Some other animals – usually predators – have their two eyes positioned on the front of their heads, thereby allowing for binocular vision and reducing their field of view in favor of stereopsis. However, front-facing eyes are a highly evolved trait in vertebrates, and there are only three extant groups of vertebrates with truly forward-facing eyes: primates, carnivorous mammals, and birds of prey. Some predatory animals, particularly large ones such as sperm whales and killer whales, have their two eyes positioned on opposite sides of their heads, although it is possible they have some binocular visual field. Other animals that are not necessarily predators, such as fruit bats and a number of primates, also have forward-facing eyes. These are usually animals that need fine depth discrimination/perception; for instance, binocular vision improves the ability to pick a chosen fruit or to find and grasp a particular branch. In animals with forward-facing eyes, the eyes usually move together.
=== Eye movements ===
Eye movements are either conjunctive (same direction) version eye movements, usually described by their type (saccades or smooth pursuit), or they are disjunctive (opposite direction) vergence eye movements. Some animals use both of the above strategies. A starling, for example, has laterally placed eyes to cover a wide field of view, but can also move them together to point to the front, so their fields overlap, giving stereopsis. A remarkable example is the chameleon, whose eyes appear as if mounted on turrets, each moving independently of the other, up or down, left or right. Nevertheless, the chameleon can bring both of its eyes to bear on a single object when it is hunting, showing vergence and stereopsis.
=== Birds === The function of two eyes seems to vary greatly between bird species. In most birds, binocular vision seems to be primarily focused on being able to control the direction of flight and being able to determine the moment at which an object will be collided: when landing or when pecking. The optical flow is important for controlling the direction of flight, which can be determined by each eye separately. Binocular overlap in that case is functional for being able to fly straight ahead, and does not necessarily indicate the ability to perceive depth. Binocular depth perception is functional in birds that use tools, such as crows. It is also functional for birds that wait still until prey is within pecking range so that they can strike at the right moment. In birds that catch their prey in the air, this area is located higher, at the point where the prey is grasped. These birds have a small binocular field of view that is focused on the area below the beak and/or near the legs, with a blind spot in the area directly below the beak. The absence of vergence eye movements means that birds cannot move the area of stereopsis, if any, in space as humans can.
=== Prevalence of stereopsis === Stereopsis has been found in many vertebrates including mammals such as horses, birds such as falcons and owls, reptiles, amphibia including toads and fish. It has also been found in invertebrates including cephalopods like the cuttlefish, crustaceans, spiders, and insects such as mantis. Stomatopods even have stereopsis with just one eye.
=== Interocular distance ===
Interocular distance, also known as pupillary or interpupillary distance, is the distance between the eyes. This separation determines the range of distances over which an animal can perceive depth.
== Applications == Applications for binocular vision are aids for binocular vision, aimed at making, recording, and viewing stereo images. The binocular microscope and binoculars can magnify images. By increasing the distance between the front lenses of the binoculars and decreasing the distance of the front lenses of the microscope, the perceived depth is in proportion to the magnification. In the course of history, various types of stereoscopes have been developed with which specially prepared stereo recordings (stereograms) can be viewed in 3D, both at home and in the cinema. The most recent development is the VR glasses.
=== Binocular viewers === The observable three-dimensional space can be seemingly enlarged with a binocular telescope for things that are far away and a binocular microscope for very small things. It is not self-evident that by enlarging the image, depth is also seen. This is explained below.