Sunday, March 2, 2008

HUMAN EYE


How does our body convert one sort of energy like light to another? Sensory transduction explains this phenomenon. Sensory transduction is the conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as light, turns into neural impulses our brains can interpret. So how the eye works is that the eye receives the light energy and manage to transform the energy into neural messages that the brain then processes into what you consciously see.

Light Energy
Many people believe that its color that strikes our eyes, but scientifically speaking, it’s the pulses of the electromagnetic energy that our visual system perceives as color. The visible light on the spectrum is a thin slice of the rest of the spectrum of electromagnetic radiation. The human eye can see from the shorter waves of blue-violet light to the longer waves of red light. In interesting fact about vision is how other organisms are sensitive to differing portions of the spectrum. Bees for an example can’t see red but can see the ultraviolet light. Different organisms react to different stimuli. There are many physical characteristics of light that determine our experience of it. Light wavelengths is the distance from one wave peak to the next and this determines the hue such as the color blue, greed, red. Intensity is the amount of energy in light and it can be determined by the amplitude or height of the waves, but the importance of amplitude is that it influences the brightness of the color we perceive. Short wavelengths equals high frequency and humans see bluish colors. Long wavelengths equals low frequency and humans sees reddish colors. Great amplitude allows us to see bright colors while small amplitudes allow us to see dull colors.

The Eye
Although the eye is small in size, it is a very complex organ. You may ask How does the eye guide an incoming ray of light toward the eye’s receptor cells you might ask, how does the eye guide an incoming ray of light toward the eye’s receptor cells? Well, first the light enters the eye through the cornea which is a protective covering that bends the light ray. Then the iris, a ring of muscle, controls the size of the pupil, through which the light enters. The lens changes shape to focus light rays on the retina which is the inner surface of the eye where receptor cells convert the light energy into neural impulses. After the retina codes the neural impulses, the impulses travel along the optic nerve to the brain. The retina receives the image upside- down, and the brain constructs the impulses it receives into an upright- seeming image. After that explanation, other questions will arise like what are the different levels of processing that occurs as information travels from the eye’s retina to the brain’s cortex. Well, processing beings in the retina’s multiple neural layers and then the retinas 6 million cones and 120 million rods relay their information via bipolar cells to ganglion cells. The impulses travel along the ganglion cells’ axons which form the optic nerve to the thalamus and on to the visual cortex. In the visual cortex which features detectors respond to specific features of the visual stimulus. Higher level super cells integrate all the data for processing in other cortical areas. But in the cortex, our assumptions, interests, and expectations influences how we process sensory information. Then you may ask, what are the rods and cones you were talking about. Well, the rods and cones have different shapes, number, function, and location that link to the brain. When light enters the eye, it triggers a photochemical reaction in the rods and cones which in turn activates bipolar cells. The bipolar cells activate ganglion cells and there axons which combines to the form the optic nerve, transmits information via the thalamus to the visual cortex in the brains; occipital region. The 120 million rods located mainly around the periphery of the retina are more sensitive to light. Multiple rods send combined messages to a bipolar cell and the pool of information let us see rough images in dim light. It is used a lot of times for night vision. Cones are concentrated in the fovea which is at the center of the retina. They are sensitive to color and detail. A cone can link directly to a single bipolar cell, and this direct line to the brain preserves fine details in the cone’s messages. Also our eyes have blind spots. Blind spot is the point at which the optic nerve leaves the eye and it creates a “blind” spot because no receptor cells are located there. Now hopefully you have a better understanding of how the eye works and how it transforms one form of energy into another.

Normal Vision and vision problems

Errors of Refraction
Some people are nearsighted, and some people are farsighted and some people have normal vision. What does all this mean? Normal vision is when the rays of light converge on the retina of a normal eye. This occurs for both nearby objects and, with appropriate readjustments in the curvature of the lens, for objects far away. These people have 20/20 vision which means it means that when you stand 20 feet away from the chart you can see what a "normal" human being can see. A Nearsighted person is able to see near objects well and has difficulty seeing objects that are far away. Nearsightedness vision is when the light rays from distant objects focus in front of the retina. When their image reaches the retina, the rays are spreading out therefore blurring the image. A farsighted person is able to see distant objects well and has difficulty seeing objects that are near. Farsighted vision is when the light rays from nearby objects come into focuses behind the retina which results in blurred images.

Color Blindness
People who are color blind can’t differentiate between different colors. The most common type is red-green color blindness and it occurs in 8 percent of males and 0.4 percent of females. This happens when either the red or green cones are not present or not functioning properly. People with this problem are not completely unable to see red or green, but often confuse the two colors. Color blindness is an inherited disorder and affects men since the capacity for color vision is located on the X chromosomes. Males only inherit on X chromosome and females inherit 2 X chromosomes so they have a better change of not getting the disorder. Since the females have two X chromosomes, they have a higher change of inheriting at least on X with normal color vision. The inability to see any color, or seeing only in different shades of gray, is very rare.

Astigmatism
Astigmatism is an uneven curvature of the cornea and causes a distortion in vision. Today we can correct a person with astigmatism by correcting the shape of the lens and making it even. We use a lens that corrects the unevenness.

Works Cited

"How Vision Works." Howstuffworks "How Vision Works". 2008. How Stuff Works. 26 Feb 2008 >.

Myers, David G. Psycgolgy . VIII. New York: Worth Publishers, 2007.

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