The Visual System PDF

THE VISUAL SYSTEM Dr. Tarek Bahaa El Deen  The Visual System The largest sector in the human nervous system is the human visual system, that capacitates the human being to handle and treat the visual details, in addition to processing and forming of imaginary images (the visual...

THE VISUAL SYSTEM Dr. Tarek Bahaa El Deen  The Visual System The largest sector in the human nervous system is the human visual system, that capacitates the human being to handle and treat the visual details, in addition to processing and forming of imaginary images (the visual perceptual response functions for non-image impulses) (Goldstein, 2010).  The Visual System The human visual system is Interacts and interprets the visible light information to structure and represent the visual environment. The responsibility of the human visual system is to perform many sophisticated functions, like the light signals reception and their transduction into electrochemical impulses, and their interpretation either through monocular vision or binocular vision. It identifies and classifies visual objects, and determines the distances between them, or between them and the viewer, and determines the direction of movement of these objects, and many various tasks to the vision process (Stone, 2012).  The Visual System The transformation of environmental stimuli into an image on the retina creates a situation that could be interpreted to indicate that the mechanism for vision is simple. According to this interpretation, if stimuli are represented as a image on the retina, the information necessary for perceiving these stimuli simply need to be extracted from this image.The component of the human visual system is: the human eye, the optic nerve , and the visual cortex (Goldstein, 2014).  The Human Eye The human eye is a complicated biological system, are 24 millimeters in diameter. The outermost layer of the eye is the conjunctiva. The small chamber formed between the transparent cornea and the colored iris is full of with a fluid called “aqueous humor”, and the eyeball itself is full of with a fluid called “vitreous humor” (Stone, 2012). The human eye has an adjustable circular aperture called the pupil, controlled by a ring of muscles within the iris (Goldstein, 2014). (Goldstein, 2014)  The Human Eye The human eye focuses the image by modifying the shape of the flexible lens, which would adopt a spherical shape but for the constant tension from ligaments that pull on it, flattening its profile. The flatter lens focuses objects at far distances. When the ring of ciliary muscles that surround it contract (Stone, 2012), however, the tension on the lens is reduced, allowing it to relax into a more spherical shape, which brings nearby objects into focus. In fact, most of the focusing power of the eye depends on the fixed shape of the cornea (Stone, 2012). www.pinterest.com  Retina “ The retina consists of sensitive photoreceptor cells which contain specific protein molecules called opsins. There are two types of opsins in the human eye: rod opsins and cone opsins. An opsin absorbs photons from light and converts them to an electrochemical signal in a stage called a signal transduction pathway” (Stone, 2012). (Stone, 2012)  Retina Rods and cones vary in their function. Rods are color-blind and operate only in low-light conditions. They are found fundamentally outside the fovea of the retina. While the cones, which are the majority in the center of the fovea, are divided into three types depending on the difference in their ability to absorb the different wavelengths. There is a type of cones sensitive to short waves or blue waves, a type of cones sensitive to medium waves or green waves, and a type of cones sensitive to long waves or red waves. Cones’ main function is to distinguish the color of objects and other features at normal light levels (Stone, 2012).  Retina Rods contain the photopigment called rhodopsin. The three different types of cones have a different type of photopigment called iodopsin: erythrolabe, in cones sensitive to electromagnetic waves called reds, chlorolabe, in cones sensitive to electromagnetic waves called greens, and cyanolabe, in cones sensitive to electromagnetic waves called blues (J., 2015).  Retina In the human retina, the photoreceptors cells send the visual information via bipolar cells and retina amacrine cells to retinal ganglion cells; then the brain will take actions and analyze the data in accordance with the vast amounts of visual processing resulting from neurological interference and the amount of visual data in the retina. “Bearing in mind that there are almost 120 million rods and 6 million cones absorb light in the retina and therefore transfers the information from the retina to the brain through the optic nerve, which is about 1.2 million nerve axes, composed of retinal ganglion cells” (Tove´e, 2008).  Retina There are several classes of retinal ganglion cells. Midget ganglion cells (Parvocellular cells), also known (P-type); are believed to be responsible for detecting details in vision, and processing color information from red and green cones. Parasol ganglion cells (Magnocellular cells), also known (M-type); are believed to be responsible for detecting motion, but can’t able to process color information. Bistratified ganglion cells (Koniocellular cells), also known (K-type); are sensitive to information in the short (blue) wavelength domain (J., 2015).  Optic nerve The optic nerves from each eye are meet and pass at what called “the optic chiasm”. Therefore the visual information that comes from the left eye is sent to the right brain hemisphere, and vice versa, the visual information that comes from the right eye is sent to the left brain hemisphere to process them. However, some of the visual information is sent to the same side of the hemisphere of the brain, like the ganglion information that comes from the temporal side of each retina (Nunez, 2010). (Nunez, 2010)  Visual cortex “The visual cortex is the largest system in the human brain and is responsible for processing the visual image. The primary visual cortex (V1) receives information directly from the LGN. Visual information then flows through V2, V3, V4, the inferotemporal cortex, MT, MST, LIP, and the FEF. Each area handles different kinds of visual information and contribute to the identification of objects and their locations in space, their color, their pattern, their shape, motion perception, intensity and quality of illuminance, and spatial localization”(Sternberg, Sternberg, & Mio, 2012). (Sternberg, Sternberg, & Mio, 2012) (Sternberg, Sternberg, & Mio, 2012)  REFERENCES Balcetis, E., & Dunning, D. (2006). See what you want to see: Motivational influences on visual perception. Journal of Personality and Social Psychology. https://doi.org/ 10.1037/0022-3514.91.4.612 Goldstein, E. B. (2010). Encyclopedia of Perception Vol. 1 & 2. Los Angeles: SAGE Publications, Inc. Goldstein, E. B. (2014). Sensation and Perception (9th ed.). Belmont: Cengage Learning. Hamd Alla, T. B. (2018a). The Cues Affecting Creation of Visual Illusion in The Digital Image Using Size Constancy. Architecture, Arts and Humanistic Science Magazine, 2(10), 119–146. Hamd Alla, T. B. (2018b). The Influence of Visual Perceptual Constancy on Attracting Attention to Digital Images on Advertising Posters. Architecture, Arts and Humanistic Science Magazine, (9th.), 112–131. J., S. P. H. and T. E. (2015). Vision and the Visual System. Oxford University Press. Macdonald, A. (2012). Windfarm Visualisation - Perspective or Perception? (1st ed.). Dunbeath: Whittles Publishing. Nunez, P. (2010). Brain, Mind, and the Structure of Reality (1st ed.). Oxford: Oxford University Press. https://doi.org/10.1093/acprof:oso/9780195340716.001.0001 Shapiro, A., & Todorovic, D. (Eds.). (2017). The Oxford Compendium of Visual Illusions (1st ed.). Oxford: Oxford University Press. https://doi.org/10.1093/acprof:oso/ 9780199794607.001.0001 Snowden Robert, Thompson Peter, T. T. (2012). Basic Vision: An Introduction to Visual Perception (Revised). Oxford University Press. Sternberg, R. J., Sternberg, K., & Mio, J. (2012). Cognitive Psychology. Science (6th ed.). Cengage Learning. Stone, J. V. (2012). Vision and brain: how we perceive the world (1st ed.). London: The MIT Press. Thompson, W., Fleming, R., Creem-Regehr, S., & Stefanucci, J. K. (2011). Visual Perception from a Computer Graphics Perspective (1st ed.). New York: CRC Pres. https:// doi.org/10.1201/b10927 Tove´e, M. J. (2008). An Introduction to the Visual System (1st ed.). Cambridge: Cambridge University Press. Ware, C. (2008). Visual Thinking for Design. Visual Thinking. https://doi.org/10.1016/B978-0-12-370896-0.00009-3