From: Date: Fri, 12 May 2000 02:06:17 EDT Subject: Third web paper To: MIME-Version: 1.0 Here is the third and final paper! Susan Lee Biology 202 2000 Third Web Report On <> Serendip Vision and Our Sense of Reality Susan Lee One aspect of human nature is to ask questions of our surroundings. Can we trust our perceptions of the world? Is in fact the reality surrounding us a stable and constant truth to which we can compare judgements? As humans assessment of our surroundings determines what we accept as real and true. Often times we accept our perceptions without question. However, can we take our perceptions as truth or does there exist a reality independent of the perceiver? Humans possess a multitude of senses to interpret surroundings; however, for the time being the discussion will be limited to the subject of vision as it pertains to the determination of reality. Vision, although not the only sense humans are dependent upon, plays a large role in the assessment of surroundings. There are two major components of vision that provide humans with a unique interpretation of the world: color and stereoscopic vision. These aspects of vision are dependent of the structure and arrangement of the ocular system. The general framework of the eye consists of photoreceptors arranged in a layer within the retina <#2 > (2).When a photon of light activates a visual pigment (rhodopsin) it undergoes conversion into a form of vitamin A, causing a change in membrane potentials and sending signals to another underlying layer of neurons <#2 > (2). Eventually the signal is carried to the brain where it is interpreted. Color perception results from the evolutionary development of three different types of rhodopsin <#2 > (2).Rhodopsin is recognized by and binds to two different types of receptors, cones and rods. Rods and cones are most effective at different levels of light. Cones are associated with color and are active during the day. Rods, on the other hand, function best at night when there is limited light. Therefore a higher occurrence of cones are found in creatures active during the day; the opposite is true of nocturnal creatures. Initially one would be tempted to make an observation that the color portrayed by any object is a property unique unto the object. However, in fact color is not a direct correlate of any given object. On can justify this by considering the different colors observed for a specific object during different times of the day i.e. the intensity of light and color during the day and the near absence of color during low light vision. Picture a red apple placed outdoors. In the morning hours, as the sun begins to rise, the apple takes on an almost orange appearance. As the day progresses and the position and intensity of lighting begin to diminish the apple appears to take on an increasingly blue tint; until, finally at night the apple is no longer red but appears blackish-blue. If color was an independent factor, the colors we observed for the apple during the daylight would be the same colors observed during the night; but this obviously is not the case. Since colors observed by humans are unique to humans, they represent a made up reality. Apples are red not because they are red but because our brains interpret the photons of light given off by the apple as red. This does not in any way deny the existence of the apple. The apple exists as a reality despite what color it is; however our perceptions of a "red" apple is a misinterpretation because the apple is red only in specific light. Therefore, in comparing the realities of the existence of the apple and its color, the existence of the apple well remain steadfast and true while its color is subject to change and not a reliable depiction of reality. Color is not the only perception that results in misinterpretations. Stereoscopic vision creates several problems in the interpretation of reality. Stereoscopic vision is unique to primates and depends on the side-by-side frontal placement of the eyes upon the face <#2 > (2). Since the eyes are oriented so, both eyes see the same scene but with slightly differing perspectives <#1> (1).When the signals are carried back to the brain, the two separate pictures are matched up. This is possible because there exists an overlap in between the two fields of vision observed by each eye<#1 > (1)<# 2> (2).Any differences between the two images is filled in and interpreted as depth, providing us with a somewhat accurate view of distance. Paintings often portray three-dimensions despite the fact that the canvas is two-dimensional. How is this accomplished? Artists depict a sense of space by using depth or distance cues. These cues are two-dimensional translations of a three-dimensional world. However, when these techniques are employed on a two-dimensional surface they create the illusion of distance/depth. Depth cues include such techniques as interposition (overlapping of objects), relative height (placement of object in relation to the horizon), relative size (more distant objects are drawn smaller) and the use of shadows <# 1 > (1). One could argue that the existence of depth cues supports an unstable reality in that one can create three-dimensional visual perceptions on a two-dimensional surface. However, such depth cues could not be derived without some constant reality to compare it with. Since the reality of our surroundings is constant, humans are able to develop believable depth cues that work and thus able to produce art work in which the observer believes that there exists more than two dimensions on the canvas. Painting is a clever way of fooling the eye into believing that what is not present is there- the creation of space. However, if we do not have a full grasp of our three-dimensional surroundings we can not begin to appreciate or understand manipulations of space. Although it seems that the sense of three-dimensions, as the majority of the western world perceives it is common to all individuals the world over, this is not the case. Experiments and observations show that a person's interpretation of the world depends upon the person's environment (the reality of their environment). One anecdote as told by anthropologist Collin Turnballs gives an account of a Bambuti pygmy's first experience in the plains after having living in the dense Ituri Forest. And then he saw the buffalo, still grazing lazily several miles away, far down below. He turned to me and said, ' What insects are those?' At first I hardly understood, then I realized that in the forest vision is so limited that there is no great need to make an automatic allowance for distance when judging size <#4 > (4). The brain provides the observer of this situation with an accurate depiction of the world; however, his analysis shows that the reality as interpreted by his sense of vision is misleading. He interpreted the scenario in ways to which he was accustomed. Other manners in which misanalysis of reality occurs is found in a study from 1960 by w. Hudson in which the cultural effects of visual perception among Bantu, European, and Indian workers and children in South Africa and Ghana compared. Test subjects were shown sets of pictures depicting a person pointing a spear at either an elephant or antelope. Present in the pictures were visual cues such as superimposition and linear perspective which supported the interpretation that the arrow was pointing at the antelope. However, when primary school aged children were asked to interpret the picture they stated that the spear was pointed at whatever subject it was aligned with, despite the presence of depth cues (4). By the end of primary school, almost all of the European children interpreted the picture correctly; but some of the Bantu and Ghanian children continued to interpret them two-dimensionally <#4 > (4). The study shows that certain depth situations must be learned through exposure and experience. Again, this shows that even if vision provides us with an accurate picture of our surroundings it is still subject to false and misleading interpretations. Optical illusions serves as another example in which visual perceptions are misleading and result in false interpretations. The works of M.C. Escher often times depicts impossible situations; yet, we can not help but analyze the piece, as we understand it from experience. For example there is an Escher piece entitled "Climbing and Descending" <#3 > (3).(, in it figures are either perpetually ascending or descending a looped staircase. The impossibility of this situation is that if the observer follows the path of the staircase in one direction it appears to be ascending; however, in the opposite direction the staircase descends. We perceive a situation that is not possible and can not exist as an independent reality, in essence we are fooled into accepting a reality that does not exist. Through the examples of misinterpretation of color and depth, one can see that we are capable of being tricked by the very system that provides us with an interpretation of our surroundings to create a reality; but how trustworthy is this reality? The colors we see are subject to change and we can be lead to believe that a two dimensional surface contains a third dimension. Even if we are provided with an accurate picture of our surroundings mistakes can be made because the ability to analyze certain situations has not yet been learned. These observations support a conclusion that a reality can in fact exist regardless of our perceptions. In the end it is not whether we have accurately interpreted or misinterpreted our surroundings; but the fact that there indeed exists something to be interpreted. WWW Sources 1) Stereo Vision Starts with Two Views , 2) 21 Senses, 3) Vision and Art , 4) Visual and Environmental factors ,