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top 10 words in brain distribution (in article): cell light human form produce animal muscle body water brain |
top 10 words in brain distribution (in article): wood build wall design structure size light surface type frame |
top 10 words in brain distribution (not in article): drink lamp wine plant beer tissue bone structure bottle process |
top 10 words in brain distribution (not in article): material paint construction window floor tree door plastic roof water |
times more probable under eye 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under desk (words not in the model) | |
Eyes'" are organs that detect light, and send signals along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in cnidaria, mollusks, chordates, annelids and arthropods. The simplest "eyes", in even unicellular organisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment. Overview. Complex eyes can distinguish shapes and colors. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception; in other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses. The first proto-eyes evolved among animals 540 million years ago, about the time of the so-called Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in 6 of the thirty-something main phyla. In most vertebrates and some mollusks, the eye works by allowing light to enter it and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye, and reducing aberrations when there is enough light. The eyes of cephalopods, fish, amphibians and snakes usually have fixed lens shapes, and focusing vision is achieved by telescoping the lens — similar to how a camera focuses. Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images. Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the world's most complex color vision system. Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye. In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents in this way the bearers can spot hot springs and avoid being boiled alive. Evolution. Visual pigments appear to have a common ancestor and were probably involved in circadian rhythms or reproductive timing in simple organisms. Complex vision, associated with dedicated visual organs, or eyes, evolved many times in different lineages. Types of eye. Nature has produced ten different eye layouts — indeed every way of capturing an image has evolved at least once in nature, with the exception of zoom and Fresnel lenses. Eye types can be categorized into "simple eyes", with one concave chamber, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface. Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution — the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures. Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomic. These two groups are not monophyletic; the cnidaira also possess cilliated cells, Pit eyes. Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eye". They are small, comprising up to about 100 cells covering about 100 µm. The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material. Pinhole eye. The pinhole eye is an "advanced" form of pit eye incorporating these improvements, most notably a small aperture (which may be adjustable) and deep pit. It is only found in the nautiloids. Without a lens to focus the image, it produces a blurry image, and will blur out a point to the size of the aperture. Consequently, nautiloids can't discriminate between objects with an angular separation of less than 11°. Shrinking the aperture would produce a sharper image, but let in less light. Spherical lensed eye. The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered — hence increasing the resolution obtainable. The most basic form, still seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges — this decreases the focal length and thus allows a sharp image to form on the retina. This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration. Such an inhomogeneous lens is necessary in order for the focal length to drop from about 4 times the lens radius, to 2.5 radii. Heterogeneous eyes have evolved at least eight times — four or more times in gastropods, once in the copepods, once in the annelids and once in the cephalopods. No aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown". This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimize the effect of eye motion while the animal moves, most such eyes have stabilizing eye muscles. The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently they can never form a sharp image. This capitulates the function of the eye. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field — this fast response is further accelerated by the large nerve bundles which rush the information to the brain. Focussing the image would also cause the sun's image to be focussed on a few receptors, with the possibility of damage under the intense | A desk'" is a furniture form and a class of table often used in a work or office setting for reading or writing on or using a computer. Desks often have one or more drawers to store office supplies and papers. Unlike a regular table, usually only one side of a desk is suitable to sit on (though there are some unusual exceptions, such as a partners desk). Not all desks have the form of a table. For instance, an Armoire desk is a desk built within a large wardrobe-like cabinet, and a portable desk is light enough to be placed on a person's lap. Early desks. Desk-style furniture appears not to have been used in classical antiquity or in other ancient centers of civilization in the Middle East or Far East, but there is no specific proof. Medieval illustrations show the first pieces of furniture which seem to have been designed and constructed for reading and writing. Before the invention of the movable type printing press in the 15th century, any reader was potentially a writer or publisher or both, since any book or other document had to be copied by hand. The desks were designed with slots and hooks for bookmarks and for writing implements. Since manuscript volumes were sometimes large, and heavy, desks of the period usually had massive structures. Desks of the Renaissance and later eras had relatively slimmer structures, and more and more drawers as woodworking became more precise and cabinet-making became a distinct trade. It is often possible to find out if a table or other piece of furniture of those times was designed to be used as a desk by looking for a drawer with three small separations (one each for the ink pot, the blotter and the powder tray) and room for the pens. The desk forms we are familiar with in this beginning of the millennium were born mostly in the 17th and 18th centuries. The ergonomic desk of the last decades is the newest addition to a long list of desk forms, but in a way it is only a refinement of the mechanically complex drawing table or drafting table of the end of the 18th century. Industrial era. Refinements to those first desk forms were considerable through the 19th century, as steam-driven machinery made cheap wood-based paper possible in the last periods of the first phase of the industrial revolution. This produced a boom in the number of, or some might say the birth of, the white-collar worker. As these office workers grew in number, desks were mass-produced for them in large quantities, using newer, steam-driven woodworking machinery. This was the first sharp division in desk manufacturing. From then on, limited quantities of finely crafted desks have been constructed by master cabinetmakers for the homes and offices of the rich while the vast majority of desks were assembled rapidly by unskilled labor, from components turned out in batches by machine tools. Thus, age alone does not guarantee that an antique desk is a masterpiece, since this shift took place more than a hundred years ago. More paper and more correspondence drove the need for more complex desks and more specialized desks, such as the rolltop desk which was a mass produced, slatted variant of the classical cylinder desk. It provided a relatively fast and cheap way to lock up the ever increasing flow of paper without having to file everything by the end of the day. Paper documents started leaving the desk as a "home," with the general introduction of filing cabinets. Correspondence and other documents were now too numerous to get enough attention to be rolled up or folded again, then summarized and tagged before being pigeonholed in a small compartment over or under the work surface of the desk. The famous Wooton desk and others were the last manifestations of the "pigeonhole" style. The newer desks could be transformed into many different shapes and angles and were ideal for artists. Steel desks. A smaller boom in office work and desk production occurred at the end of the 19th century and the beginning of the 20th with the introduction of smaller and cheaper electrical presses and efficient carbon papers coupled with the general acceptance of the typewriter. Steel desks were introduced to take heavier loads of paper and withstand the pounding meted out on the typewriters. The L-shaped desk became popular, with the "leg" being used as an annex for the typewriter. Another big boom occurred after the Second World War with the spread of photocopying. Paperwork drove even higher the number of desk workers, whose work surface diminished in size as office rents rose, and the paper itself was moved more and more directly to filing cabinets or sent to records management centers, or transformed into microfilm, or both. Modular desks seating several co-workers close by became common. Even executive or management desks became mass-produced, built of cheap plywood or fiberboard covered with wood veneer, as the number of persons managing the white collar workers became even greater. Student desks. A "'student desk'" can be any desk form meant for use by a student. Usually the term designates a small pedestal desk or writing table constructed for use by a teenager or a pre-teen in his or her room at home. More often than not it is a pedestal desk, with only one of the two pedestals and about two thirds of the desk surface. Such desks are sometimes called left pedestal desks or right pedestal desks depending on the position of the single pedestal. The height of the desk is usually a bit lower than is the case for normal adult desks. In some cases, the desk is connected from the seat to the table. The table is also used for sitting before classes. The desks are usually mass-produced in steel or wood and sold on the consumer market. In addition there is a wide variety of plans available for woodworking enthusiasts. There are many novel forms of student desks made to maximize the relatively restricted area available in a child's room. One of the most common is the bunk bed desk, also known as a loft bed. Impact of computers. Until the late 1980s desks remained a place for paperwork and business negotiation. At the end of this decade though the personal computer was taking hold in large and medium sized businesses. New office suites included a "knee hole" credenza which was a place for a terminal or personal computer and keyboard tray. Soon new office designs also included "U-shape" suites which added a bridge worksurface between the back credenza and front desk. During the North American recession of the early 1990s, many manager and executive workers had to do word processing and other functions previously completed by typing pools and secretaries. This necessitated a more central placement of the computer on these "U-shape" suite desk systems. With computers abounding, "computer paper" became an office staple. The beginning of this paper boom gave birth to the dream of the "paperless office", in which all information would appear on computer monitors. However, the ease of printing personal documents and the lack of comfort with reading text on computer monitors led to a great deal of document printing. The need for paperwork space vied with the rising desk space taken up by computer monitors, CPUs, printers, scanners, and other peripherals. As well, the need for more space led some desk companies to attach some items to the modesty panel at the back of the desk, such as multi-outlets and cabling. Through the "tech boom" of the 1990s, office worker numbers skyrocketed along with the cost of office space rent. The cubicle desk became widely accepted in North America as an economical way of putting more desk workers in the same space without actually shrinking the size of their working surfaces. The cubicle walls have become new place for workers to affix papers and other items once left on the horizontal desktop surface. Even computer monitor frames themselves are used to attach reminder notes and business cards. Early in the 2000s, private office workers found that their side and back computer-placing furniture made it hard to show the contents of a computer screen to guests or co-workers. Manufacturers have responded to this issue by creating "Forward Facing" desks where computer monitors are placed on the front of the "U-shape" workstation. This forward computer monitor placement promotes a clearer sight-line to greet colleagues, increases computer screen privacy and allows for common viewing of information displayed on a screen. References. Articles and books on real and virtual desks and things in between: |