We do not see the world in black and white; neither do we see it as two-dimensional (2-D) or flat (just height and width, no depth). Let’s look at how color vision works and how we perceive three dimensions (height, width, and depth). Color Vision Normal-sighted individuals have three different types of cones that mediate color vision. Each of these cone types is maximally sensitive to a slightly different wavelength of light. According to the trichromatic theory of color vision, shown in Figure 1, all colors in the spectrum can be produced by combining red, green, and blue. The three types of cones are each receptive to one of the colors. The trichromatic theory of color vision is not the only theory—another major theory of color vision is known as the opponent-process theory. According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa. One of the implications of opponent processing is that we do not experience greenish-reds or yellowish-blues as colors. Another implication is that this leads to the experience of negative afterimages. An afterimage describes the continuation of a visual sensation after removal of the stimulus. For example, when you stare briefly at the sun and then look away from it, you may still perceive a spot of light although the stimulus (the sun) has been removed. When color is involved in the stimulus, the color pairings identified in the opponent-process theory lead to a negative afterimage. You can test this concept using the flag in Figure 2. But these two theories—the trichromatic theory of color vision and the opponent-process theory—are not mutually exclusive. Research has shown that they just apply to different levels of the nervous system. For visual processing on the retina, trichromatic theory applies: the cones are responsive to three different wavelengths that represent red, blue, and green. But once the signal moves past the retina on its way to the brain, the cells respond in a way consistent with opponent-process theory (Land, 1959; Kaiser, 1997). Depth Perception Our ability to perceive spatial relationships in three-dimensional (3-D) space is known as depth perception. With depth perception, we can describe things as being in front, behind, above, below, or to the side of other things.
Our world is three-dimensional, so it makes sense that our mental representation of the world has three-dimensional properties. We use a variety of cues in a visual scene to establish our sense of depth. Some of these are binocular cues, which means that they rely on the use of both eyes. One example of a binocular depth cue is binocular disparity, the slightly different view of the world that each of our eyes receives. A 3-D movie works on the same principle: the special glasses you wear allow the two slightly different images projected onto the screen to be seen separately by your left and your right eye. Although we rely on binocular cues to experience depth in our 3-D world, we can also perceive depth in 2-D arrays. Think about all the paintings and photographs you have seen. Generally, you pick up on depth in these images even though the visual stimulus is 2-D. When we do this, we are relying on a number of monocular cues, or cues that require only one eye. If you think you can’t see depth with one eye, note that you don’t bump into things when using only one eye while walking—and, in fact, we have more monocular cues than binocular cues. An example of a monocular cue would be what is known as linear perspective. Linear perspective refers to the fact that we perceive depth when we see two parallel lines that seem to converge in an image (Figure 3). Vision is not an encapsulated system. It interacts with and depends on other sensory modalities. For example, when you move your head in one direction, your eyes reflexively move in the opposite direction to compensate, allowing you to maintain your gaze on the object that you are looking at. This reflex is called the vestibulo-ocular reflex. It is achieved by integrating information from both the visual and the vestibular system (which knows about body motion and position). You can experience this compensation quite simply. Finally, vision is also often implicated in a blending-of-sensations phenomenon known as synesthesia.
Cancer registries are part of the national NCD surveillance system. Population-based registries provide invaluable information on the trends in cancer incidence, while hospital-based registries provide information on the clinical diagnosis, cancer staging, treatment modalities, and survival outcomes. In Japan, cancer incidence is monitored through population-based and hospital-based cancer registries by the Japanese Association of Cancer Registries, in collaboration with 34 prefectural governments. The registries are supported and maintained by the Research Center for Cancer Prevention and Screening at the National Cancer Center. In Singapore, a comprehensive population-, clinic-, hospital-, and laboratory-based cancer registration has been performed by the Singapore Cancer Registry since 1968. Comprehensive cancer registration has been achieved through collation of data obtained from a combination of sources: (1) physician notifications, (2) pathology records, (3) hospital records, and (4) mortality data from the national Registry of Births and Deaths. Since 2009, cancer notification has been made mandatory to ensure completeness of surveillance.
Detection of colon cancer before the development of symptoms results in a cure more frequently.
A lower end of the digestive tract cancer that affects the colon or rectum. Early cases may start as benign polyps. Although they frequently show no symptoms, screening can find them. Doctors advise testing for patients at high risk or over 50 for this reason.
The size and location of the disease affect the symptoms of colorectal cancer. Changes in bowel habits, adjustments to stool consistency, blood in the stool, and discomfort in the abdomen are a few symptoms that are frequently felt.
Screening means checking your body for cancer before you have symptoms. Thus, screening done before the development of the symptom will help the doctors to start the treatment early and hence the cancer can be cured in the right time before it starts developing symptoms.
The epithelial tissue is the tissue that is mostly exposed to the external environment. The epidermis is the outermost layer of the skin, it is a type of epithelial tissue, covering large spaces of the body. It consists mostly of dense accumulations of cells attached to each other that allow them to communicate with each other.
