Binocular single vision

In biology, binocular vision is a type of vision in which an animal having two eyes is able to perceive a single three-dimensional image of its surroundings. Neurological researcher Manfred Fahle has stated six specific advantages of having two eyes rather than just one: In biology, binocular vision is a type of vision in which an animal having two eyes is able to perceive a single three-dimensional image of its surroundings. Neurological researcher Manfred Fahle has stated six specific advantages of having two eyes rather than just one: Other phenomena of binocular vision include utrocular discrimination (the ability to tell which of two eyes has been stimulated by light), eye dominance (the habit of using one eye when aiming something, even if both eyes are open), allelotropia (the averaging of the visual direction of objects viewed by each eye when both eyes are open), binocular fusion or singleness of vision (seeing one object with both eyes despite each eye's having its own image of the object), and binocular rivalry (seeing one eye's image alternating randomly with the other when each eye views images that are so different they cannot be fused). Binocular vision helps with performance skills such as catching, grasping, and locomotion. It also allows humans to walk over and around obstacles at greater speed and with more assurance. Optometrists and/or orthoptists are eyecare professionals who fix binocular vision problems. The term binocular comes from two Latin roots, bini for double, and oculus for eye. Some animals - usually, but not always, prey animals - have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. Examples include rabbits, buffaloes, 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, but not always, predatory animals - 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, eyes on the front is 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 predator 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. The direction of a point relative to the head (the angle between the straight ahead position and the apparent position of the point, from the egocenter) is called visual direction, or version. The angle between the line of sight of the two eyes when fixating a point is called the absolute disparity, binocular parallax, or vergence demand (usually just vergence). The relation between the position of the two eyes, version and vergence is described by Hering's law of visual direction.