Because their sensitivities overlap, cones work in combination to convey information about all visible colors. The human eye contains three types of cones (red, green and blue), each sensitive to a different range of colors.

Most of our vision, however, comes from cones that work under most light conditions and are responsible for acute detail and color vision. Rods constitute 95 percent of all photoreceptors in humans. Rods are extremely sensitive to light and allow us to see in dim light, but they do not convey color. Two major types of photoreceptors are rods and cones. Photoreceptors, about 125 million in each human eye, are neurons specialized to turn light into electrical signals. Studies about the inner workings of the retina give us the best knowledge we have to date about how the brain analyzes and processes sensory information. Scientists know much about the way cells encode visual information in the retina, but relatively less about the lateral geniculate nucleus - an intermediate way station between the retina and visual cortex - and the visual cortex. A similar arrangement applies to movement and touch: Each half of the cerebrum is responsible for processing information received from the opposite half of the body. Conversely, the right half of the scene registers in the cerebrum’s left hemisphere. The result is that the left half of the scene you are watching registers in the cerebrum’s right hemisphere. This visual information then maps to the right side of the cortex. When you look at a scene with both eyes, the objects to your left register on the right side of the retina.

This crossover allows both sides of the brain to receive signals from both eyes. Visual signals pass from each eye along the million or so fibers of the optic nerve to the optic chiasm, where some nerve fibers cross over. Primates, including humans, have well-developed vision using two eyes, called binocular vision. The shape of the lens is altered by the muscles just behind the iris so that near or far objects can be brought into focus on the retina. The size of the pupil, which regulates how much light enters the eye, is controlled by the iris. The signals are then sent via the optic nerve to other parts of brain, which ultimately processes the image and allows us to see.Īs in a camera, the image on the retina is reversed: Objects to the right of center project images to the left part of the retina and vice versa objects above the center project to the lower part and vice versa. Photoreceptors gather visual information by absorbing light and sending electrical signals to other retinal neurons for initial processing and integration.

Nervous system lens