How we see?

Take a look around the room that you are in. Notice how the various images and colors that you see update constantly as you turn your head and re-direct your attention. Although the images appear to be seamless, each blending imperceptibly into the next, they are in reality being updated almost continuously by the vision apparatus of your eyes and brain. The seamless quality in the images that you see is possible because human vision updates images, including the details of motion and color, on a time scale so rapid that a "break in the action" is almost never perceived. The range of color, the perception of seamless motion, the contrast and the quality, along with the minute details, that most people can perceive make "real-life" images clearer and more detailed than any seen on a television or movie screen. The efficiency and completeness of your eyes and brain is unparalleled in comparison with any piece of apparatus or instrumentation ever invented. We know this amazing function of the eyes and brain as the sense of vision.

From the beginning of time humans have tried to explain the complex process of vision. It is interesting to examine a few of the ancient theories and to compare them to our modern knowledge. Recorded studies of human vision date back at least to the time of Aristotle. Aristotle was a prominent philosopher, scientist, and scholar who lived in ancient Greece around the 4th century BC. Aristotle studied many scientific issues and published his thoughts in a variety of texts. Aristotle's explanation of the process of human vision was that the object being looked at somehow altered the "medium" (now known to be air) between the object itself and the viewer's eye. This alteration of the medium was thought to propagate to the eye, allowing the object to be seen. During the Middle Ages Aristotle's theory was reversed. Instead of postulating that the object itself had innate properties which allowed vision, popular theory of the time suggested that the viewer's eyes sent out emissions to the object and that those emissions enabled vision to occur. These theories may seem strange, unsatisfying or illogical today, but remember that the theories of long ago were not based on today's extensive experimental scientific data. Instead they were based on the conjecture and observation of scholars. Thanks to the knowledge generated by countless generations of scholars and scientists using increasingly sophisticated tools in pursuit of scientific knowledge our understanding of vision has come a very long way!

Vision is a complicated process that requires numerous components of the human eye and brain to work together. The initial step of this fascinating and powerful sense is carried out in the retina of the eye. Specifically, the photoreceptor neurons (called photoreceptors) in the retina collect the light and send signals to a network of neurons that then generate electrical impulses that go to the brain. The brain then processes those impulses and gives information about what we are seeing. In this unit we will investigate the initial steps in the process of vision. We will discover how the photoreceptors work, and will specifically examine at the photoreceptor proteins to learn how light energy is converted into electrical energy. Additionally, we will examine some of the current studies that are helping to further our understanding of the proteins involved in the vision process.