What is binocular vision

binocular vision

binocular vision [from Latin. bini = two each, ocularis = concerning the eyes], Binocular vision,E. binocular vision, simultaneous viewing with both eyes (see additional information); it enables a spatial impression of depth (spatial vision, stereoscopic vision, plastic vision, stereopsis) to win and estimate distances (distance vision). Each eye perceives an object from a different perspective, which means that the images on the retina are slightly shifted from one another (and also somewhat distorted). These shifts are neurally offset against each other and combined again to form an image (binocular fusion). The difference between the different viewing angles of the two eyes is called binocular disparity (disparation). The human visual system can perceive disparities of up to a few arc seconds. The disparity creates an impression of depth and is mainly used for the detailed spatial analysis of an object. An imaged object point must be in a certain retinal area of ​​the second eye, the so-called Panum area, can be mapped. If it lies outside this zone, no binocular fusion takes place and one arises Double image (Diplopia). In the human fovea (fovea centralis) the panum area has an extension of approx. 8 minutes of arc, at 10 ° in the periphery it is approx. 30 minutes of arc. However, the dimensions of the panum area are not fixed, but vary depending on the type of visual stimulus. Within the area, the impression of depth changes with a slight displacement of the object, while the fusion remains stable. All points that are mapped to corresponding retinal coordinates lie on a circular line, the Horopter. Due to the Panum areas, the horopter is a ring that contains all points that merge binocularly. The further away a point is from the fixation point in the horopter, the greater the disparity. If an object lies in front of the horopter, it comes to crossed disparity, whereby the object is imaged in both temporal halves of the retina. In the uncrossed disparity if the object is behind the horopter and is consequently displayed on both nasal halves. Thus, on the one hand, the size of the disparity is a measure of the distance to the fixation point (Distance measurement), on the other hand, the type of disparity (crossed or uncrossed) provides information about the position relative to the fixation point. - Corresponding retinal points project onto the same regions in the visual brain. The first neurons with binocular receptive fields are located in the entry point of the visual cortex V1. You receive signals from non-corresponding retinal areas in both eyes. These binocular neurons specialize in various disparities (disparation-sensitive neurons) and thus for binocular depth vision (Stereopsis) responsible. - For example, if you follow an object moving from left to right with both eyes, you will see objects in front of the object earlier with your right eye, and objects behind the object later than with your left eye. These time differences are converted into depth perception by the visual brain, with the maximum difference being around 50 ms. If you hold a gray filter in front of one eye and look at a pendulum swinging back and forth, it appears to describe an elliptical path. The reason is that the eye with the gray filter receives the visual signal with a delay, which is answered by the visual brain with apparent depth. It is not absolutely necessary to look at an object at the same time in order to perceive disparities. With special glasses it is possible to darken one eye alternately very quickly. Even at frequencies of a few Hertz you can create a depth perception. Field of view, field of view, monocular vision, stereoscopy.

F.St./H.H.

binocular vision

binocular vision in animals:

The size of the binocular field of view correlates with the lifestyle of the individual. Animals that actively catch prey or that visually control their limb coordination have a large binocular field of view. In primates it reaches a size of 150 °, in cats 130 °, in birds of prey and the praying mantis around 60 °. Animals that fear predators and therefore need to recognize them early on have their eyes on the sides of their heads. This increases your overall field of view, but you only have a small binocular field. The pigeon, for example, has a total field of vision of 340 ° with a binocular portion of only 35 °. In some of these species (rabbits, flies) there is also a second binocular field behind the animal. In such animals with a sideways eye position, the optic nerve fibers cross almost completely in the optic chiasm, so that each eye projects into the opposite hemisphere. The signals from the corresponding areas of the retina are then brought together via the bar (corpus callosum). In contrast, in animals with a large binocular field, there is a partial crossover in the optic chiasm (also in humans), so that signals from corresponding retinal locations run together into the brain. - Animals with complex eyes, like vertebrates, cannot make eye convergence movements (eye movements) inward to fixate on a nearby object. Rather, the visual axes of corresponding pairs of ommatidia on the inner sides of the eyes give them information about the distance of a fixed object. The further inside this pair is, the closer the intersection is to the animal. Ommatidia located in the front of the eye with almost parallel axes of vision are not suitable for this. In the predatory dragonfly larvae, the majority of the ommatidia of the binocular field of view exactly cover the striking area of ​​their capture mask. The praying mantis uses binocular vision to determine the distance and speed of prey. It follows the prey by means of head saccades and strikes at a suitable distance of 20-30 mm, corresponding to a disparity of 10 °. If one eye is covered, her binocular vision is impaired and she misses it. If you put a light-refracting prism in front of a praying mantis eye, it hits too far, even though it has correctly determined the disparity of 10 °. When presenting two prey objects, she prefers to strike at the closer one. Two laterally offset prey objects are perceived by both complex eyes in different regions. It arises from the crossing of two visual axes (left eye fixes right prey, right eye fixes left prey) Ghost-Picture. You can get the praying mantis to strike at this ghost if you cover the two outer lines of sight (left eye fixes left prey, right eye fixes right prey).