Video: How Does The Cat See?
The structure of a cat's eye is basically the same as that of a human. Vision is based on the ability of organisms to detect light - the visible portion of electromagnetic radiation.
Organ of vision - the eye perceives light thanks to the retina, which is part of the brain. Light enters the retina through the pupil. With the help of a special muscle, the pupil changes its size and, like a diaphragm in a camera, regulates the flow of light to the retina. In nocturnal animals, the eyes are large, with a large pupil; in daytime animals, they are much smaller. In cats that see in the dark, but like to bask in the sun, the pupil is slit-like, since it is better than round, it reduces the light flux to the sensitive retina.
The anterior transparent membrane of the eye - the cornea and the lens suspended on the muscles and ligaments immediately behind the pupil refract the light flux, like the optical system of a camera, and focus the image of the object on the retina. When viewing objects at different distances from the eyes, accommodation occurs - the image is focused exactly on the retina by changing the shape of the lens. The ability for such accommodation in cats and dogs is 2-3 times less than in higher monkeys and humans.
On the retina, the light flux hits the photoreceptors. Photoreceptors are cells containing a colored substance - a pigment, which, under the influence of light, discolor, while the pigment molecules change their shape, which leads to the appearance of an electric potential. Photoreceptors vary in shape and are divided into two types: rods and cones. The sticks contain one pigment, so they provide twilight colorless vision. There are three types of pigments in the cones, they form the basis of color daytime vision. The ratio of rods to cones in animals of different species is different. The ability to distinguish small details (visual acuity) is provided by cones.In the retina, there is a place of best vision, which in humans has the shape of a fossa, and in a cat it is a disc. Cones are mainly located here. Turns of the head and gaze help the image of the object fall into the area of better vision on the retina.
In many nocturnal animals, including a cat, special formations are located near the photoreceptors - the tapetum, reflecting the light not absorbed by the retinal cells back onto the photoreceptors, which provides better vision at dusk. The eyes of animals that have tapetum glow in the dark.
In the retina, in addition to photoreceptors, there are also several layers of nerve cells, from which an electrical signal enters the brain through the optic nerve. The paths from the right and left eyes intersect, so information from both eyes arrives in each hemisphere of the brain. The spaces that the cat sees with the right and left eyes (visual fields) overlap in front by 45% so that the animal can see the same object with both eyes at the same time. This underlies the animal's ability to determine the shape of an object and the distance to it. Cats from a distance of one meter distinguish the distance of the platform to which they jump, with an accuracy of 3-5 cm.
Animal behavior, guided by sight, is largely dependent on learning. This has been demonstrated in a dedicated study. The kittens were raised for up to 8 weeks in the dark, and then from 8 to 12 weeks in an installation, which was a carousel with two booths. In one booth the kitten was sitting, and in the second the kitten was strengthened so that it walked with its paws on the floor and drove the first kitten. After such a four-week training, the kitten, which walked on its own, performed well on tests for determining floor height, landing on its feet and others; and the one who only looked around made mistakes in all tests.
Related article Perception of heat and cold in a cat
Information from the retina enters the visual cortex, where the most essential processing takes place.Nerve cells in the cerebral cortex change their activity depending on whether the cat is shown a luminous line, a spot or a mouse. If cats lose their eyesight at an early age, then the area of neurons associated with vision in the cerebral cortex decreases, and due to them the number of neurons associated with distinguishing between auditory and skin stimuli increases. The whiskers of these cats become 30% longer than those of sighted cats. The increased role of hearing, smell and other sense organs compensates for the loss of vision so well that the behavior of such animals is no different from that of normal animals. However, disturbances in the cerebral visual structural will lead to the fact that the delicate psyche of animals, the nuances of mood will not be reflected in the beautiful eyes of the cat.
Source: Natalia Shvyrkova, "Cat and Dog" magazine 1997 - 4