Eye Senses and Vision: How the Human Eye Works, Sees Light, and Perceives Color.
The eye, of course, is only one part of the visual system.
Eye: The eyes are connected to each other by their sensory nerves.
The optic nerve extends along the diencephalon and travels along the occipital lobes of both hemispheres. The eyes receive stimuli that generate neural signals that return between the brain and the cortex and processes that enable patterns of grouping and organization of objects in the cortex.
The human eye is a visual recording device like a camera. Actually, it's a camera. The sensitive plate is the retina, which differs from the photographic plate in that the explorer recovers after each exposure to be ready for the next view.
Eye: The eyes are connected to each other by their sensory nerves.
The optic nerve extends along the diencephalon and travels along the occipital lobes of both hemispheres. The eyes receive stimuli that generate neural signals that return between the brain and the cortex and processes that enable patterns of grouping and organization of objects in the cortex.
The human eye is a visual recording device like a camera. Actually, it's a camera. The sensitive plate is the retina, which differs from the photographic plate in that the explorer recovers after each exposure to be ready for the next view.
Structure of the human eye
The human eye is an organ that interacts with light and has many purposes, just like the sensory organs in the mammalian eye.
Rod cells and neurons in the retina allow conscious light perception and vision, including color discrimination and depth perception. The human eye can distinguish about 10 million colors.
As in the eyes of other mammals, the photosensitive ganglion cells of the human eye in the retina receive a light signal that affects pupil size.
Near the front of the eye where light enters is the raised colored iris with a hole in the middle we call the pupil.
The iris has small muscle fibers that regulate the shape of the purple eighth cross to the adjustable camera diaphragm. The front part of the eye consists of the curved, transparent cornea; a strong lens directly behind the pupil; and another lens whose curvature is adjusted by small ciliary muscles.
This muscle corresponds to the camera's focusing mechanism. Through it the eye focuses on near or distant objects, and the transparent fluid allows light to reach the retina. The retina is a thin membrane.
It lines the back of the eyeball and contains sensory cells that connect neurons to the brain.
Rod cells and neurons in the retina allow conscious light perception and vision, including color discrimination and depth perception. The human eye can distinguish about 10 million colors.
As in the eyes of other mammals, the photosensitive ganglion cells of the human eye in the retina receive a light signal that affects pupil size.
Near the front of the eye where light enters is the raised colored iris with a hole in the middle we call the pupil.
The iris has small muscle fibers that regulate the shape of the purple eighth cross to the adjustable camera diaphragm. The front part of the eye consists of the curved, transparent cornea; a strong lens directly behind the pupil; and another lens whose curvature is adjusted by small ciliary muscles.
This muscle corresponds to the camera's focusing mechanism. Through it the eye focuses on near or distant objects, and the transparent fluid allows light to reach the retina. The retina is a thin membrane.
It lines the back of the eyeball and contains sensory cells that connect neurons to the brain.
Visual receptors
Sensory cells in the retina are of two types: rods and cones. The incoming lights cause chemical and electrical changes in the rods and cones.
The cones have more developed cells than the rods in the fovea, which is a small depression in the retina directly below the pupil. There are only cones, and this is the center of clear vision. When we look directly at a small object, in order to see it clearly, we turn our eyes so that the object's light falls on the fovea. Outside this small central area, rods and cones merge, with fewer cones farther into the retina. The farther you go, the less the difference in shape and color. From this fact we conclude that form and color vision are largely cone dependent.
The cones have more developed cells than the rods in the fovea, which is a small depression in the retina directly below the pupil. There are only cones, and this is the center of clear vision. When we look directly at a small object, in order to see it clearly, we turn our eyes so that the object's light falls on the fovea. Outside this small central area, rods and cones merge, with fewer cones farther into the retina. The farther you go, the less the difference in shape and color. From this fact we conclude that form and color vision are largely cone dependent.
Eye movement:
The eyeball is rotated by 6 muscles in the socket, and the eyes are linked together at their motor nerve center to show almost perfect teamwork in their movement.
They make two coordinated movements, looking here and there around the landscape: the eyes are like a pair of parallel horseshoes. This is the conjugate movement of the eyes. But I change from a distant object to a background object. The eyes converge so that the foveae of both eyes receive light from the particular object being looked at.
Conjugate motion recorded by photography has been found to be of two types.
This is called the jump or saccade movement and the pursuit movement. A saccade movement moves the eye from one object to another, while a pursuit movement follows a moving object.
They make two coordinated movements, looking here and there around the landscape: the eyes are like a pair of parallel horseshoes. This is the conjugate movement of the eyes. But I change from a distant object to a background object. The eyes converge so that the foveae of both eyes receive light from the particular object being looked at.
Conjugate motion recorded by photography has been found to be of two types.
This is called the jump or saccade movement and the pursuit movement. A saccade movement moves the eye from one object to another, while a pursuit movement follows a moving object.
Noor: What is it?
Light is a form of energy called electromagnetic radiation, which also includes radio waves and sound waves. Only a small fraction of this radiation can be seen. That is, our eyes can detect only a small fraction of this radiation. It is best to think of light as consisting of waves that have different frequencies and intensities.
The intensity of the light determines the brightness of the visual sensation. The light reflected from an apple lit by a candle will be of low intensity, so we see the red color of the apple as dim rather than bright. The frequency of the light wave largely determines the colors we see. That is, light waves of different wavelengths are perceived as different colors.
The intensity of the light determines the brightness of the visual sensation. The light reflected from an apple lit by a candle will be of low intensity, so we see the red color of the apple as dim rather than bright. The frequency of the light wave largely determines the colors we see. That is, light waves of different wavelengths are perceived as different colors.
How do we see brightness?
The perception of brightness begins when light is absorbed by the receptor rods in the retina. These rods are highly sensitive to light intensity and are specifically designed to function under low-light conditions. When light strikes the rods, it triggers a series of chemical and electrical reactions, activating a chain of neurons that carry the visual signals through the optic nerve to the brain. The intensity of the light directly influences the level of activity generated in the retina. The greater the intensity, the stronger the stimulation of the rods and the more vigorous the neural activity transmitted to the brain. As a result, the sensation of brightness that we perceive becomes stronger. In simple terms, brighter light causes greater retinal and neural activation, leading to a more vivid experience of brightness in our visual perception.
How do we see colors?
Color vision is the ability of the human eye to distinguish between different wavelengths of light, independently of their intensity or brightness. This complex visual function allows us to perceive a wide range of colors and is primarily facilitated by specialized photoreceptor cells called cones, located in the retina. There are three types of cones in the human eye, each sensitive to a specific range of light wavelengths. Some cones respond best to blue light, others to green light, and some to red light. When light enters the eye, these cones are activated based on the wavelength they are most responsive to, and they send signals to the brain accordingly.
However, our perception of color is not determined by cone activity alone. The brain enhances this process through a mechanism known as opponent processing, which occurs in specialized neurons called opponent cells, particularly within the lateral geniculate nucleus (LGN) of the brain. These cells are designed to compare inputs from different cones. For example, certain opponent cells become excited when stimulated by red wavelengths and inhibited when exposed to green wavelengths, while others are excited by blue and inhibited by yellow. This balance of excitatory and inhibitory impulses enables the visual system to detect subtle contrasts and differences between colors.
Through this sophisticated processing system, the brain interprets the combined input from the cones and opponent cells, producing a full spectrum of color perception. Even when two light sources share similar brightness levels, the variation in wavelength allows us to distinguish between them as different colors. This neural interaction also contributes to color constancy, the phenomenon that allows us to recognize colors consistently even under different lighting conditions. The integration of cone responses and opponent cell activity ensures that humans experience a rich and accurate perception of the colorful world around them.
However, our perception of color is not determined by cone activity alone. The brain enhances this process through a mechanism known as opponent processing, which occurs in specialized neurons called opponent cells, particularly within the lateral geniculate nucleus (LGN) of the brain. These cells are designed to compare inputs from different cones. For example, certain opponent cells become excited when stimulated by red wavelengths and inhibited when exposed to green wavelengths, while others are excited by blue and inhibited by yellow. This balance of excitatory and inhibitory impulses enables the visual system to detect subtle contrasts and differences between colors.
Through this sophisticated processing system, the brain interprets the combined input from the cones and opponent cells, producing a full spectrum of color perception. Even when two light sources share similar brightness levels, the variation in wavelength allows us to distinguish between them as different colors. This neural interaction also contributes to color constancy, the phenomenon that allows us to recognize colors consistently even under different lighting conditions. The integration of cone responses and opponent cell activity ensures that humans experience a rich and accurate perception of the colorful world around them.
Color blindness.
Some people are colorblind. Color blindness is the partial or complete inability to distinguish colors. It is usually a sex-related disorder. Men develop this recessive trait more easily than women. There are different ways to develop color blindness. People with color blindness cannot distinguish between light colors such as pink or tan. Most people with color blindness have difficulty distinguishing between red and green, especially at poor saturation. There are rare ones that confuse yellow and blue. About one or two people in a thousand are the rarest, with no color visible at all. Color blindness is rare, and most people with color blindness are able to distinguish only a few colors. The most common form of color blindness, occurring in 10% of men and 1% of women, is red-green. People with red-green color blindness may see red and green as yellow-gray. They often confuse blue with yellow. Yellow blindness is rare and usually occurs only as a result of disease.
People who can see all colors are called trichromats. People with red-green or blue-yellow color deficiency are called dichromats (two colors), and people with color blindness are called monochromats (one color).
People who can see all colors are called trichromats. People with red-green or blue-yellow color deficiency are called dichromats (two colors), and people with color blindness are called monochromats (one color).