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Invisibility

Invisibility

Invisibility refers to the state of an object which cannot be seen. An object in this state is said to be invisible (literally, "not visible"). The term is usually used as a fantasy/science fiction term, where objects are literally made unseeable by magical or technological means. However, its effects can also be seen in the real world, particularly in physics. Since objects can be seen by light in the visible spectrum from a source reflecting off their surfaces and hitting the viewer's eye, the most natural form of invisibility (whether real or fictional) is an object which does not reflect light (that is - allows light to pass through it). In nature, this is known as transparency, and is seen in many naturally-occurring materials (although no naturally-occurring material is 100% transparent). Visibility also depends on the eyes of the observer and/or the instruments used. Thus an object can be classified as "invisible to" a person, animal, instrument, etc.

Invisibility by Environment

An object may be classified as "invisible" if it cannot be seen due to environmental factors other than the fact that it doesn't reflect light. An object that might normally be seeable may be classified as invisible if it is:
- Behind an object.
- The same colour or pattern as the background. (Camouflage)
- Patterned so that its outline is hard to determine.
- In an environment which is too dark or too bright.
- Not in a particular observer's line-of-sight. (Especially when driving)
- Transparent. (air and many other gases)

Invisibility in Physics

Theoretical and practical physics offer several causes of invisibility. An object may be invisible if it is:
- So massive that its escape velocity exceeds the speed of light (e.g. a black hole)
- Emitting or reflecting light outside the wavelength range of visible light. (Radiation is generally invisible by this means). Unfortunately, this would result in any obscured human being becoming not invisible and transparent, but completely opaque and resembling a human-shaped black hole.
- So tiny that it cannot be detected by an observer.

Invisibility by Technology

Technology can be used theoretically or practically to render real-world objects invisible:
- Making use of real-time image displayed on a wearable display, scientists are able to create a see-through effect, if not invisibility. This is known as optical camouflage and has been used in many science fiction works.
- It has been speculated that an object could appear invisible if light were bent around it.
- Invisibility (lower visibility) for radar is called stealth technology.
- Often a hypothetical "cloaking device" can be used to make objects invisible.
- In filmmaking, people, objects, or backgrounds can be made to look invisible on-camera through a process known as bluescreen (or greenscreen).

Invisibility by Magic

Invisibility, usually by magic, is a popular theme in fantasy, mythology and Ceremonial magic. It is often used as a gameplay device in role-playing and strategy games. Typically, people or objects can be rendered completely invisible by several means:
- Magical objects such as rings, cloaks and amulets can be worn to grant the wearer permanent invisibility.
- Magical potions can be consumed to grant temporary invisibility.
- Magic spells can be cast on people or objects, usually giving temporary invisibility.
- Some mystical creatures can make themselves invisible at will, such as Chinese dragons in some tales, which can shrink so small that humans cannot see.
- An invisibility ritual part of one of the manuscript of the Hermetic Order of the Golden Dawn as it appears on the Book "The Golden Dawn" transliterated by Israel Regardie. Where magical invisibility is concerned, the issue may arise of whether or not the clothing and items carried by the invisible wearer/carrier are also rendered invisible. In general, they are, but in some instances, clothing remains visible and must be removed for the full invisibility effect.

Examples of Invisibility in Fiction

The idea of being unseen and hence undetectable has fascinated mankind for generations. This concept of invisibility has been explored in many myths, novels, movies and video games, some of them comedies.
- Mythology and folklore
- In many myths and legends, gods, spirits, fairies, angels, and demons are often invisible or can choose to become invisible at will.
- The ring of Gyges is described in a story in Plato's The Republic. A peasant finds a ring in the tomb of a dead king which allows him to become invisible at will. Plato has him enter the palace, seduce the queen, and plot to kill the king, arguing that power, such as this, corrupts absolutely.
- The hero Perseus went equipped with a helmet of invisibility to kill Medusa.
- A magic cloak, made by Alberich the dwarf, granted invisibility to Sigurd.
- In German fairy tales, magical caps called tarnkappes are worn by dwarfs. The caps can make an entire village of dwarfs invisible.
- Modern fiction
- The Invisible Man (1897) by H. G. Wells is a well-known novel about invisibility, later made into a film and several TV series.
- One function of the One Ring in J. R. R. Tolkien's The Lord of the Rings series was to render the user invisible. Unfortunately, it had an evil influence with negative effects on the wearer's actions.
- The Philadelphia Experiment (1984) is a movie about an attempt to make a ship invisible.
- The film Predator and animated television series like Batman Beyond and Max Steel depict a a kind of stealth mode that is a partial invisibility where the subject is largely transparent and/or translucent. While a concentrated look can spot it, it still makes the wearer extremely hard to see which eases stealth movement. Such a suit may actually be possible (see External links below).
- The Harry Potter series of novels and movies featured a cloak of invisibility that, when worn, makes the covered body parts, including the clothing beneath the cloak invisible, the cloak itself and perhaps also the contents of the pockets, invisible. The cloak does not stop one from being solid or making noise. When one wears an Invisibility Cloak in a crowd, the wearer has to take great care to not knock into anyone, which leads to awkward questions.
- In comic books, there are superheroes such as the Invisible Woman (who can bend light around herself without distortion) that have the power to become invisible at will as well as wizards like Doctor Strange who have invisibility spells in their possession.
- In the film Mystery Men (1999), the "Invisible Boy" is invisible when nobody is looking at him.
- In the film Hollow Man (2000), an injection is tested on animals (and eventually, humans) which made the organism invisible, organ by organ. Unfortunately, the serum also causes serious side effects.
- In The Hitchhiker's Guide to the Galaxy "trilogy" of novels by Douglas Adams, the Somebody Else's Problem field is a humorous concept of a field which makes people believe the object in question is "somebody else's problem" and therefore do not see it.
- In the Star Trek universe, some ships of the Klingon Empire and the Romulan Star Empire, as well as the Federation ship USS Defiant, are equipped with pieces of hardware known as cloaking devices that conceal them from most varieties of scans, including visual.
- Cloaking technology is also employed by large battleships in the game Colony Wars.
- In Metal Gear Solid, Otacon wore a stealth camoflauge prototype while sneaking around the facility to provide you help. Ninja also used a similar suit. The Fear used it in Metal Gear Solid 3: Snake Eater as well. It is also an unlockable item that the player can use to thwart his enemies.
- Blizzard Entertainment's strategy games have always had invisibility as a gameplay device. For example, in StarCraft, many units employ cloaking devices, while in Warcraft III, units employ a range of invisibility spells and camouflage at night time.
- In The Incredibles, one of the family members, Violet Parr (Vi) has the ability to render her invisible to people. The ability is for her body only. A suit is made for her that can also go invisible when she does.
- The short story "They Go Bump" by David Barr Kirtley is about a group of soldiers who wear invisibility suits. The main character has trouble walking (not being able to see his feet) and starts to wonder if his invisible companions are really who they say they are.
- The videogame, Psychonauts features invisibility as one of many psychic powers unlocked and made available to the player throughout the game. The power can be used to escape enemies, and it particularly useful during boss encounters.
- In the book series Artemis Fowl, fairies can vibrate at a very high frequency, making them invisible all creatures except rats and two species of monkeys.

Theory of Sight While Invisible

This theory states that while a person is totally invisible (however this could be achieved), they would actually be blind. We are able to see things (Visual perception) when light hits the back of the eye. Since the back of the eye would be invisible, light would pass through it. The eye would not then even know light was there, and certainly couldn't pass that information on to the brain to translate into a visual image. Therefore, when somebody next asks "What would you do if you were invisible for the day?", consider your new disability before answering.

External links

- [http://www.guardian.co.uk/print/0,3858,4199601-103419,00.html Info on "stealth suit"]
- [http://members.aol.com/doder1/invisib1.htm Some examples]
- [http://www.cnn.com/2003/TECH/02/07/japan.invisible.ap CNN article on an "actual" invisibility suit]
- Note: the picture was taken by a special camera that displays images behind the wearer of the suit. The suit itself does not render invisibility. In essence, the suit functions as a bluescreen onto which the image behind the suit can be displayed through camera.
- [http://www.nature.com/news/2005/050228/full/050228-1.html Theoretical method of scattering light] that could make objects "invisible" to certain light frequencies.
- Unfortunately, this could not be used to hide anything but a microscopic object from visible light because the object has to be the same size as the wavelength of light from which it is hidden.
- [http://www.straightdope.com/mailbag/mvisiblelight.html Brief piece on why visible light is visible]

Visual perception

Visual perception is one of the senses, consisting of the ability to detect light and interpret (see) it as the perception known as sight or naked eye vision. Vision has a specific sensory system, the visual system. There is disagreement as to whether or not this constitutes one, two or even three distinct senses. Some people make a distinction between "black and white" vision and the perception of colour, and others point out that vision using rod cells uses different physical detectors on the retina from cone cells. Some argue that the perception of depth also constitutes a sense, but others argue that this is really cognition (that is, post-sensory) function derived from having stereoscopic vision (two eyes) and is not a sensory perception as such. Many people are also able to perceive the polarization of light.

The visual system

thumbnailThe eye is the light-sensitive organ that is the first component of the visual system. The eye's retina performs the first stages of visual perception processing, with the remaining stages of visual perception occurring in the optic nerve, the lateral geniculate nucleus, and the visual cortex of the brain.

Sources of information

To perform its task, visual perception takes into account not only patterns of illumination on the retina, but also our other senses and our past experiences. Consider the task of bird sighting (an instance of object recognition): to be able to identify a bird against a background of tree and brushes, one needs prior exposure to general properties of the bird category. From past experiences, we expect birds to have a certain shape, color, etc. Hearing a sound that is characteristic of birds, a song for example, will help us locate one: information from the other senses is used in visual perception. In this case, locational information from the auditory domain is used.

Individual and group differences in visual perception

Most of the general processes of visual perception have been shown to be universal, as opposed to being dependant on culture, although there are specific instances where cultural variability appears to come into play. It has also been shown that certain individual differences such as impairment of sight and spatial skills can also affect our visual perception. There are also other factors that influence how we perceive things such as personality, cognitive styles, gender, occupation, age, values, attitudes, motivation, religious beliefs, economic status, education and habits.

Theoretical perspectives in the study of visual perception

Unconscious inference

Hermann von Helmholtz is often credited with the founding of the scientific study of visual perception. Helmholtz held vision to be a form of unconscious inference: vision is a matter of deriving a probable interpretation for incomplete data. The general goal of vision is to identify, as accurately as possible, the features of our environment: roughly, what objects are present where. Other features are irrelevant to this task : illumination patterns, viewing position, etc. Those are confounding variables. Call S = (F,C) the scene, with F the features we’re interested in and C the confounding variables. S determines I, the pattern of illumination on the retina, which is all the information our visual system has on the current scene. The task is to find S given I. This problem is under-constrained: many different S correspond to the same I, and many I could correspond to the same S. One of the reasons is that much information is lost when a 3-dimensional world is collapsed into a 2-dimensional array. To see why, consider the figure of a circle such as this one: O. It could correspond to an infinity of ellipses viewed at a certain slant. But we always interpret it as a circle viewed on the frontal plane – the explanation we infer from the data for this particular stimulus. Inference requires prior assumptions about the world: two well-known assumptions that we make in processing visual information are that light comes from above and that objects are viewed from above not below. The study of visual illusions (cases when the inference process goes wrong) has yielded a lot of insight into what sort of assumptions the visual system makes.

Gestalt

Psychologists of the Gestalt school have raised a large part of the research questions that still preoccupy vision scientists today. The so-called Gestalt Laws of Organisation have broadened the study of how people perceive objects to be organized patterns or wholes, instead of collections of many separate parts. Gestalt is a German word that translates to "configuration or pattern". According to this theory, there are four main factors that determine how we group things according to visual perception.
- Proximity – Depending on how close object are to one other, we tend to group the ones closest to each other as a group.
- Similarity – If objects are similar in shape or size to one another we tend to group them together.
- Closure – How we complete a pattern because of how the items are grouped together even though the pattern is not complete.
- Simplicity – How we group items according to symmetry, regularity, and smoothness.

Ecological psychology

Psychologist James J. Gibson developed a theoretical perspective on vision that is radically different from that of Helmholtz. Gibson considers that enough visual perception is available in normal environments to allow for veridical perception (accurate perception of the world). Gibson replaces inference with information pickup. Although most researchers today feel closer to Helmholtz's unconscious inference theory, Gibson has done much in identifying what sort of information is available to the visual system.

Types of visual perception

- Black and white vision
- Color vision
- Gestalt perception
- Motion perception

Disorders/Dysfuntions

- Achromatopsia
- Color blindness
- Scotopic Sensitivity Syndrome

References

- Rudolph Arnheim (1954). Art and Visual Perception: A Psychology of the Creative Eye. Berkeley: University of California Press.
- Lothar Kleine-Horst (2001). Empiristic Theory of Visual Gestalt Perception. Hierarchy and Interactions of Visual Functions. Koeln: Enane. ISBN 3-928955-42X

External links

- [http://enane.de/cont.htm Empiristic theory of visual gestalt perception]
- [http://www.aber.ac.uk/media/Modules/MC10220/visper03.html Visual Perception 3 - Cultural and Environmental Factors]
- [http://www.sapdesignguild.org/resources/optical_illusions/gestalt_laws.html Gestalt Laws]
- [http://www.aber.ac.uk/media/Modules/MC10220/visper04.html Visual Perception 4 - Individual Differences, Purposes and Needs] Category:Computer vision Category:Vision ja:視覚

Science Fiction

Science fiction

Technology

:See also: Innovation Innovation.]] Technology is a word with origins in the Greek word technologia (τεχνολογια), techne (τεχνη) "craft" + logia (λογια) "saying". It is an encompassing term dealing with the use and knowledge of humanity's tools and crafts.
Disambiguation of technology
Depending on context, the word technology has the following definitions and uses:
- Technology as tool-In its most common usage, technology is the tools and machines that help to solve problems. In this usage, technology is a far-reaching term that can include both simple tools, such as a wooden spoon, and complex tools, such as the space station.
- Technology as technique-In this usage, technology is the current state of our knowledge of how to combine resources to produce a desired products, to solve a problem, to fulfill a need, or to satisfy a want. Technology in this sense includes technical methods, skills, processes, techniques, tools and raw materials. (such as artificial intelligence, building technology, or medical technology).
- Technology as culture former-a culture-forming (or destroying) activity (such as manufacturing technology, infrastructure technology, or space-travel technology). (McGinn). As a cultural activity, technology predates both science and engineering. This is not to imply that technology is the only culture forming activity, nor that it is the primary culture-forming activity. Often, it is dominant in cultural formation; often, it is not. In addition, culture may act to form technology. Due to widespread, and sometime careless, use of technology, several other topics arise in the study of technology, including technological ethics, environmental impacts, technological by-products, and technological risk, among many other philosophical and sociological topics.

Science and technology

The lines between science and technology are not always clear. Generally, science is the reasoned investigation or study of nature, aimed at finding out the truth, generally according to the scientific method. Technology is the application of knowledge (scientific, engineering, and/or otherwise) to achieve a practical result (Roussel, et.al.). For example, science might study the flow of electrons in an electric current. This knowledge may be used to create artifacts, such as semiconductors, computers, and other forms of technology.

History of technology

The history of technology is as old as the history of humanity because history proper refers to what could be recorded by technological means. Mind you that other animals currently use tools and animals prior to human existence may have as well. The history of technology follows a progression from simple (low-tech) tools and simple energy sources to complex ("hi-tech") tools. The earliest technologies converted natural resources into simple tools. Processes such as carving, chipping, scraping, rolling (the wheel), and sun-baking are simple means for the conversion of raw materials into usable products. Anthropologists have uncovered many early human houses and tools made from natural resources (although birds also build nests out of dried materials and we don't consider them to have a technological society). The use, and then mastery, of fire was a key turning point in man's technological evolution providing him with simple energy. The use of fire extended the capability for the treatment of natural resources and allowed the use of natural resources that require heat to be useful. Wood and charcoal were among the first materials used as a fuel. Wood, clay, and rock (such as limestone), would be among the earliest materials shaped or treated by fire, for making weapons, pottery, bricks, and cement, among others. Continuing improvements such as the furnace enabled the ability to smelt and forge metal (such as copper, ca. 8000 BC), and eventually to the discovery of alloys, such as brass and bronze (ca. 4000 BC). The first uses of iron alloys, steel, dates to around 1400 BC. Complex tools include both simple machines (such as the lever (ca. 300 BC), the screw (ca. 400 BC), and the pulley) and complex machines (such as the ocean liner, the engine, the computer, modern communications devices, the electric motor, the jet engine, among many others). Again we are confronted with an impractical vagueness as we categorise the lever with the jet engine. As tools increase in complexity, so does the type of knowledge needed to support them. Modern complex machines require written technical manuals of collected information that his been countinually added to and improved upon and are so complex, that entire technical knowledge-based processes and practices (also complex tools themselves) exist to support them, including engineering, medicine, computer science, etc. Further, complex machinies require complex manufacturing and construction techniques and organizations. Entire industries have arisen to support and develop complex tools.

The nature of technology

General characteristics

With all of the technology in use in modern society, it may seem futile to attempt a generalized list of common characteristics. Many authors, such as McGinn (1991) and Winston (2003), list the following: Complexity refers to the characteristic that most modern tools are difficult to understand. Some are easy to use, but difficult to comprehend source and means of make, such as a kitchen knife, or a baseball. Others are both difficult to use and difficult to comprehend, such as a tractor, gasoline, a television, or a computer. Dependency refers to the fact that modern tools depend on other modern tools, which depend on other modern tools, for their make and their use. Cars, as an example, have a huge complex of industry of means and methods. And to use them requires a complex of road, streets, highways, and gasoline stations, waste collection, etc., beyond our comprehension. Valence refers to the many, many different types of the same tool. Imagine the many different types of spoons available today, or scissors, and even complex tools come in many shape as well, like the construction crane, or the automobile. Scale refers to the sheer magnitude, size, and pervasiveness of modern technology. Simply put, technology seems to be everywhere. It dominates modern life. Scale refers also to the magnitude of some modern technological projects, like the cellular telephone network, the Internet, air travel, satellites, etc.

Types of Technology

One possible classification of technology uses the fields of technological studies, commonly found in academic institutions of higher learning:
- Applied Science;
- Athletics and recreation;
- The Arts and language;
- Business/information;
- Defense;
- Domestic/residential;
- Engineering;
- Health;
- Cognitive;
- Travel and trade .

Relationship with society

The relationship between society and technology is quite complex, creating what many characterize as a co-dependence upon the other; society creates and depends upon technology to meet its needs and desires, and technology's very existence arises due to society's needs and desires. However, this "symbiosis" goes further than that: Every advancement in technology influences and eventually changes society. So the needs of society change, creating more needs, and, eventually, creating more technology. (McGinn 1991) Consider the telephone, and its latest sibling the mobile phone. With the invention of the telephone, society began to depend on quicker ways of communication with others. Higher expectations for quicker communications were initially met using short-range radio systems for use in emergency vehicles. However, even higher portability was realized with miniaturization of components. This demand for a new product led to the invention of the mobile phone. The influence of portability is so pervasive now anyone can be accessible to talk in most urban places in the developed world Many technologies allow one society to have a military advantage over another society. This can be indirectly as something that creates population growth, for example, or this can be direct technology put into use like the gun or the atom bomb. The effects these technologies have on human society are complex and could result in slavery, assimilation, or genocide. Some technologies, like the video camera, start without militaristic use but eventually find themselves employed for those purposes. The car is another example of this... it is created and marketed with the promise of freedom (initially for the wealthy and without regard to the factory hands) but then it impedes upon other forms of transportation (like the free movement of the pedestrian), requires extensive paving for its full accommodation, and then it is employed militaristically. Its consumption of fuel eventually even becomes the potential basis for a resource war. The use of advanced mass media techniques, such as television programming, allows some members of society to have larger sway over the attititudes and opinions of others. Mass media often shapes mass opinion -- for better or, at least as often, worse. The effects that various forms of technology have upon the environment also sways public opinion. The Chernobyl effect (caused by a massive nuclear meltdown) is thought to have played a part in undermining the confidence that citizens of the Soviet Union had in their government. The exact causes for the collapse of that government are debatable but the new leader in Russia had a reputation as being a strong environmentalist.

Funding for technological development

Government

The government is a major contributor to the development of technology. In the United States, many agencies invest millions of dollars in new technology. In 1980, the UK government invested just over 6 million pounds in a 4 year Programme, later extended to 6 years, called the Microlectronics Education Programme (MEP) which aimed to provide every school in Britain with at least one computer, microprocessor training materials and software, plus extensive teacher training.

Military technology

Technology has frequently been driven by the military, with most modern applications being developed for the military before being taken up for civilian use. However, this trend has recently seen a reversal, with the industry often taking the lead in developing technology which is then adopted by the military.

Other

Some government agencies are dedicated specifically to research, such as the American's National Science Foundation, the United Kingdom scientific research institutes, the American's Small Business Innovative Research effort. And many government agencies dedicate a major portion of their budget to research and development.

Private source

For profit

Research and development is one of the biggest investments made by corporations toward new and innovative technology.

Non-profit

Many foundations and non-profit organizations contribute to the development of technology.

Side effects

There are two types of effects from the use of technology, main effects and side effects. Main effects are those intended by the technology, usually to fulfill some desire or need. Side effects are (usually) unintended, and often unknown prior to technology's implementation. This portion of the article deals with those side effects.

Sociological

The most subtle side effects from technological uses are sociological in nature. Subtle because those side effects can go unnoticed without careful observation and contemplation of individual, institutional, and group behaviors.

Values

The implementation of technology influence the values (beliefs, ideas, opinions) of society by changing expectations and realities. There are (at least) three major, interrelated, values that are the result of technological innovations:
- Mechanistic World View. A set of beliefs that views the universe as a collection of parts, like a machine, that can be individually analyzed and understood. (McGinn)
- Efficiency. A value, originally applied only to machines, but now placed upon all aspects of society, whereby each element (organizational structures and human beings) is expected to attain higher and higher performance, output, ability, etc. (McGinn)
- Progressivism. The belief that societal progress is good.

Ethics

Winston provides an excellent summary of the ethical implications of technological development and deployment. He states there are four major ethical implications:
- Challenges traditional ethical norms.
- Creates an aggregation of effects.
- Changes the distribution of justice.
- Provides great power.

Lifestyle

In many ways, technology simplifies life.
- The rise of a leisure class
- More informed
- Sets the stage for more complex learning tasks
- Increases multi-tasking
- Global Networking
- Creates denser social circles
- others In other ways, technology complicates life.
- Sweatshops and harsher forms of slavery are more likely to be found in technologically advanced societies (relative to primitive societies).
- More people are currently starving now that at any point in history or pre-history
- Work to drive to drive to work to work to drive -- consequently dealing with the traffic jams.
- the prison population grows with advancements in jailing techniques and tools.
- Too much information
- Consumerism
- Pace
- Technicism
- New forms of danger
- Can cause obesity and laziness
- Distraction among students-internet, gaming, etc. can take away from academic performance

Institutions and groups

Technology influences, often enables, organizational and bureaucratic group structures and influence. Example of this include:
- The rise of organizations: e.g., health institutions.
- The commericalization of leisure: sports events, products, etc. (McGinn)
- The advent of large organizational structures.
- Others

International

Technology provides a heightened awareness of international issues, values, and cultures. Due mostly to mass transportation and mass media, the world seems to be a much smaller place due to the following, among others:
- Globalization of ideas
- Embeddedness of values
- Population growth and control
- Others

Environmental

The effects of technology on the environment is both obvious and subtle. The more obvious effects include the depletion of nonrenewable natural resources (such as petroleum, coal, ores), and the added pollution of air, water, and land. The more subtle effects include debates over long-term impacts (e.g., global warming, deforestation, natural habitat destruction, costal wetland loss) Others

Control

Autonomous technology

In one line of thought, technology develops autonomously, in other words technology seems to feed on itself, moving forward with a force irresistible by humans. To these individuals, technology is "inherently dynamic and self-augmenting." (McGinn, p. 73) Jacques Ellul is one proponent of the irresistibleness of technology to humans. He espouses the idea that humanity cannot resist the temptation of expanding our knowledge and our technological abilities. He, however, does not believe that these seeming autonomy of technology is inherent. But the perceived autonomy is due to the fact that humans do not adequately consider the responsibility that are inherent to technological processes. Another proponent of these ideas is Langdon Winner who believes that technological evolution is essentially beyond the control of individuals or society.

Government

Individuals rely on governmental assistance to control the side effects and negative consequences of technology. Government intervenes many through laws.
- Supposed independence of government. An assumption commonly made about the government is that their governance role is neutral or independent. Often, if not usually, that assumption is misplaced. Governing is a political process, more so in some countries than in others, therefore government will be influenced by political winds of influence. In addition, government provides much of the funding for technological research and development. Therefore, even government has a vested interest in certain outcomes.
- Liability. One means for controlling technology is to place responsibility for the harm with the agent causing the harm. Government can allow more or less legal liability to fall to the organization(s) or individual(s) responsibile for damages.
- Legislation.
- Others

Choice

Society also controls technology through the choices that it makes. These choices not only include consumer demands; it includes
- the channels of distribution, how do products go from raw materials to consumption to disposal;
- the cultural beliefs regarding style, freedom of choice, consumerism, materialism, etc.;
- the economic values we place on the environment, individual wealth, government control, capitalism, etc.
- Others

Technology and philosophy

Technicism

Generally, Technicism is an overreliance or overconfidence in technology as a benefactor of society. Taken to extreme, some argue that technicism is the belief that humanity will ultimately be able to control the entirety of existence using technology. In other words, human beings will eventually be able to master all problems, supply all wants and needs, possibly even control the future. (For a more complete treatment of the topic see the work of Egbert Schuurman, for example at [http://scholar.lib.vt.edu/ejournals/SPT/v3n1/schuurman.html].) Some, such as Monsma, et al., connect these ideas to the abdication of God as a higher moral authority. More commonly, technicism is a criticism of the commonly held belief that newer, more recently-developed technology is "better." For example, more recently-developed computers are faster than older computers, and more recently-developed cars have greater gas efficiency and more features than older cars. Since current technologies are generally accepted as good, future technological developments are not considered circumspectly, resulting in what seems to be a blind acceptance of technological developments.

Optimism, pessimism and appropriate technology

Pessimism

On the somewhat pessimistic side, are certain philosophers like Herbert Marcuse, Jacques Ellul, and John Zerzan, who believe that technological societies are inherently flawed a priori. They suggest that the result of such a society is to become evermore technological at the cost of freedom and psychological health (and probably physical health in general as pollution from technological products is dispersed). Perhaps the most poignant criticisms of technology are found in what are now considered to be literary classics, for example Aldous Huxley's Brave New World, Anthony Burgess's A Clockwork Orange, and George Orwell's Nineteen Eighty-Four.

Optimism

On the other hand, the optimistic assumptions are made by proponents of technoprogressivist views or ideologies such as transhumanism and singularitarianism, that view technological development as generally having beneficial effects for the society and the human condition. In these ideologies, technological development is morally good. Some critics see these ideologies as examples of scientism, mathematical fetishism, or techno-utopianism and fear the idea of technological singularity which they support.

Appropriate technology

The notion of appropriate technology, however, was developed in the twentieth century to describe situations where it was not desirable to use very new technologies or those that required access to some centralized infrastructure or parts or skills imported from elsewhere. The eco-village movement emerged in part due to this concern.

Theories and concepts in technology

There are many theories and concepts that seek to explain the relationship beteen technology and society:
- Appropriate technology
- Diffusion of innovations
- Jacques Ellul's Technological Society, is considered a classic criticism of modern culture's pursuit of technology for its own sake. For more on these ideas see http://www.usd.edu/~ssanto/ellul.html.
- Intermediate technology, more of an economics concern, refers to compromises between central and expensive technologies of developed nations and those which developing nations find most effective to deploy given an excess of labour, and scarcity of cash. In general, a so-called "appropriate" technology will also be "intermediate".
- Persuasion technology, in economics, definitions or assumptions of progress or growth are often related to one or more assumptions about technology's economic influence. Challenging prevailing assumptions about technology and its usefulness has led to alternative ideas like uneconomic growth or measuring well-being. These, and economics itself, can often be described as technologies, specifically, as persuasion technology — a concern covered in its own separate article.
- Posthumanism
- Precautionary principle
- Strategy of technology
- Technocapitalism
- Radovan Richta's theory of technological evolution
- Technological determinism
- Technological diffusion
- Technological singularity
- Technology acceptance model
- Technology lifecycle
- Technology transfer
- Transhumanism

References

- Adas, Michael. Machines as the Measure of Men: Science, Technology, and Ideologies of Western Dominance, Cornell University Press, 1990.
- Nobel, David. Forces of Production: a social history of industrial automation, New York: Knopf 1984, Paperback Edition: Oxford University Press, 1990.
- McGinn, Robert E. Science, Technology and Society, Englewood Cliffs, New Jersey, 1991.
- Monsma, S.V., C. Christians, E.R. Dykema, A. Leegwater, E. Schuurman, and L. VanPoolen. Responsible Technology. Grand Rapids, Michigan (USA): W.B. Eerdmans Publishing Company, 1986.
- Roussel, P.A., K. N. Saad, and T. J. Erickson. Third Generation R&D, Cambridge, Massachusetts: Harvard Business School Press, 1991.
- Winston, M.E. "Children of Invention", in Society, Ethics, and Technology, Second Edition, M.E. Winston and R.D. Edelbach (eds.), Belmont, California (USA): Wadsworth Group/Thomson Learning, 2003.
- Smil, Vaclav. Energy in World History, Boulder, CO: Westview Press, 1994, pp. 259-267, as quoted in http://www.thenagain.info/webchron/Technology/Technology.html, maintained by David W. Koeller, Northpark University, Chicago, Illinois (USA), downloaded September 11, 2005.

External links

- [http://www.pneumatica.be basic pneumatics]
- [http://www.memoryzine.com/cognitivetechnolgy.html Cognitive Technology Journal]
- [http://www.elsevier.com/wps/find/bookdescription.cws_home/525392/description#description Cognitive Technology, Elsevier]
- [http://topics.developmentgateway.org/egovernment Development Gateway's e-Government Page] — Depository of various e-government technology resources.
- [http://www.greatachievements.org/ Greatest Engineering Achievements of the 20th Century]
- [http://technologybusiness.blogspot.com/ The Business of Technology]
- ko:기술 ms:Teknologi ja:工業 th:เทคโนโลยี

Eye

: This article refers to the sight organ. See Eye (disambiguation) for other usages An eye is an organ that detects light. Different kinds of light-sensitive organs are found in a variety of creatures. The simplest eyes do nothing but detect whether the surroundings are light or dark. More complex eyes are used to provide the sense of vision. Many complex organisms including some mammals, birds, reptiles and fish have two eyes which may be placed on the same plane to be interpreted as a single three-dimensional "image" (binocular vision), as in humans; or on different planes producing two separate "images" (monocular vision), such as in rabbits and chameleons.
Varieties of eyes
chameleon chameleon]] 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, where the light is detected and converted into electrical signals, which 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 which regulates the intensity of the light that enters the eye. 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 give a pixelated image (not multiple images as is often believed). 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 (many Strepsiptera) have compound eye composed of a few facets each with a retina capable of creating an image, which does provide muliple image vision. With each eye viewing a different angle, a fused image from all the eyes is produced in the brain providing a very wide angle high resolution image. 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. Some of the simplest eyes, called ocelli, can be found in animals like snails, who can not actually "see" in the common 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 (day and night), but no more. This enables snails to keep out of direct sunlight. Jumping spiders have simple eyes that are so large, supported by an array of other smaller eyes, that they can get enough visual inputs to hunt and pounce on their prey. Some insect larvae like caterpillars have a different type of single eye (stemmata) which gives a rough image.
Evolution of eyes
How a complex structure like the projecting eye could have evolved is often said to be a difficult question for the theory of evolution. Darwin famously treated the subject of eye evolution in his Origin of Species: :To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. Despite the precision and complexity of the eye, computer models of eye evolution, developed by Dan-Erik Nilsson and Susanne Pelger, demonstrated that a primitive optical sense organ could evolve into a complex human-like eye within a reasonable period (less than a million years) simply through small mutations and natural selection. Eyes in various animals show adaption to their requirements. For example, birds of prey have much greater visual acuity than humans and some, like diurnal birds of prey, can see ultraviolet light. The different forms of eye in, for example, vertebrates and mollusks are often cited as examples of parallel evolution, suggesting that the development of eyes through evolution might not be so improbable as it might seem. However, the development of the eye is considered to be monophyletic; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago (Mya).
Anatomy
monophyletic monophyletic The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. All of the individual components through which light travels within the eye before reaching the retina are transparent, minimising dimming of the light. The cornea and lens help to converge light rays to focus onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain. Light enters the eye from an external medium such as air or water, passes through the cornea, and into the first of two humours, the aqueous humour. Most of the light refraction occurs at the cornea which has a fixed curvature. The first humour is a clear mass which connects the cornea with the lens of the eye, helps maintain the convex shape of the cornea (necessary to the convergence of light at the lens) and provides the corneal endothelium with nutrients. The iris, between the lens and the first humour, is a coloured ring of muscle fibres. Light must first pass though the centre of the iris, the pupil. The size of the pupil is actively adjusted by the circular and radial muscles to maintain a relatively constant level of light entering the eye. Too much light being let in could damage the retina, too little light would be blinding. The lens, behind the iris, is a convex, springy disk which focuses light, through the second humour, onto the retina. To clearly see an object far away, the circularly arranged ciliary muscles will pull on the lens, flattening it. Without muscles pulling on it, the lens will spring back into a thicker, more convex, form. Humans gradually lose this flexibility with age, resulting in the inability to focus on nearby objects, which is known as presbyopia. There are other refraction errors arising from the shape of the cornea and lens, and from the length of the eyeball. These include myopia, hyperopia, and astigmatism. On the other side of the lens is the second humour, the vitreous humour, which is bounded on all sides: by the lens, ciliary body, suspensory ligaments and by the retina. It lets light through without refraction, helps maintain the shape of the eye and suspends the delicate lens. Wrapped around these tissues are three layers of tissue surrounding the vitreous humour. The outermost is the sclera which gives the eye most of its white colour. It consists of fibrin connective tissue and both protects the inner components of the eye and maintains its shape. On the inner side of the sclera is the choroid, which contains blood vessels that supply the retinal cells with necessary oxygen and removes the waste products of respiration. Within the eye, only the sclera and ciliary muscles contain blood vessels. The choroid gives the inner eye a dark colour, which prevents disruptive reflections within the eye. The inner most layer of the eye is the retina, containing of the photosensitive rod and cone cells, and neurons. To maximise vision and light absorption, the retina is a relatively smooth (but curved) layer. It does have two points at which it is different; the fovea and blind spot. The fovea is a dip in the retina directly opposite the lens, which is densely packed with cone cells. It is largely responsible for colour vision in humans, and enables high acuity, such as is necessary in reading. The blind spot is a point on the retina where the optic nerve pierces the retina to connect to the nerve cells on its inside. No photosensitive cells exist at this point, it is thus "blind". In some animals, the retina contains a reflective layer (the tapetum lucidum) which increases the amount of light each photosensitive cell perceives, allowing the animal to see better under low light conditions.
Other articles regarding eye anatomy
Aqueous humour, Anterior chamber, Blind spot, Canal of Schlemm, Ciliary body, Ciliary muscle, Cornea, Conjunctiva, Choroid, Fovea, Iris, Lens, Macula, Optic disc, Optic nerve, Ora serrata, Posterior chamber, Pupil, Retina, Sclera, Suspensory ligament, Tapetum lucidum, Trabecular meshwork, Vitreous humour, Zonular fibers.
Cytology
The retina contains two forms of photosensitive cells - rods and cones. Though structurally and metabolically similar, their function is quite different, though they are equally important to vision. Rod cells are highly sensitive to light allowing them to respond in dim light and dark conditions. These are the cells which allow humans and other animals to see by moonlight, or with very little available light (as in a dark room). However, they do not distinguish between colours, and have low visual acuity (a measure of detail). This is why the darker conditions become, the less colour objects seem to have. Cone cells, conversely, need high light intensities to respond and have high visual acuity. Different cone cells respond to different colours (wavelengths) of light, which allows an organism to see colour. The differences are useful; apart from enabling sight in both dim and light conditions, humans have given them further application. The fovea, directly behind the lens, consists of mostly densely-packed cone cells. This gives humans a highly detailed central vision, allowing reading, bird watching, or any other task which primarily requires looking at things. Its requirement for high intensity light does cause problems for astronomers, as they cannot see dim stars, or other objects, using central vision because the light from these is not enough to stimulate cone cells. Because cone cells are all that exist directly in the fovea, astronomers have to look at stars through the "corner of their eyes" where rods also exist, and where the light is sufficient to stimulate cells, allowing the individual to observe distant stars. Rods and cones are both photosensitive, but respond differently to different frequencies of light. They both contain different pigmented photoreceptor proteins. Rod cells contain the protein rhodopsin and cone cells contain different proteins for each colour-range. The process through which these proteins go is quite similar - upon being subjected to electromagnetic radiation of a particular wavelength and intensity (ie. a colour visible light) the protein breaks down into two constituent products. Rhodopsin, of rods, breaks down into opsin and retinal; iodopsin of cones breaks down into photopsin and retinal. The opsin in both opens ion channels on the cell membrane which leads to the generation of an action potential (an impulse which will eventually get to the visual cortex in the brain). This is the reason why cones and rods enable organisms to see in dark and light conditions - each of the photoreceptor proteins requires a different light intensity to break down into the constituent products. Further, synaptic convergence means that several rod cells are connected to a single bipolar cell, which then connects to a single ganglion cell and information is relayed to the visual cortex. Whereas, a single cone cell is connected to a single bipolar cell. Thus, action potentials from rods share neurons, where those from cones are given their own. This results in the high visual acuity, or the high ability to distinguish between detail, of cone cells and not rods. If a ray of light were to reach just one rod cell this may not be enough to stimulate an action potential. Because several "converge" onto a bipolar cell, enough transmitter molecules reach the synapse of the bipolar cell to attain the threshold level to generate an action potential. Furthermore, colour is distinguishable when breaking down the iodopsin of cone cells because there are three forms of this protein. One form is broken down by the particular EM wavelength that is red light, another green light, and lastly blue light. In simple terms, this allows human beings to see red, green and blue light. If all three forms of cones are stimulated equally, then white is seen. If none are stimulated, black is seen. Most of the time however, the three forms are stimulated to different extents - resulting in different colours being seen. If, for example, the red and green cones are stimulated to the same extent, and no blue cones are stimulated, yellow is seen. For this reason red, green and blue are called primary colours and the products of mixing two secondary colours. The secondary colours can be further complimented with primary colours to see tertiary colours.
Acuity
Visual acuity can be measured with several different metrics. Cycles per degree (CPD) measures how much an eye can differentiate one object from another in terms of degree angles. It is essentially no different from angular resolution. To measure CPD, first draw a series of black and white lines of equal width on a grid (similar to a bar code). Next, place the observer at a distance such that the sides of the grid appear one degree apart. If the grid is 1 meter away, then the grid should be about 8.7 millimeters wide. Finally, increase the number of lines and decrease the width of each line until the grid appears as a solid grey block. In one degree, a human would not be able to distinguish more than about 12 lines without the lines blurring together. So a human can resolve distances of about 0.73 millimeters at a distance of one meter. A horse can resolve about 14 CPD (0.62 mm at 1 m) and a rat can resolve about 1 CPD (8.7 mm at 1 m). A diopter is the unit of measure of focus.
Dynamic range
At any given instant, the retina can resolve a contrast ratio of around 100:1 (about 6 1/2 stops). As soon as your eye moves (saccades) it re-adjusts its exposure both chemically and by adjusting the iris. Hence, over time, a contrast ratio of about 1,000,000:1 (about 20 stops) can be resolved.
Adnexa and related parts

The orbit
In many species, the eyes are inset in the portion of the skull known as the orbits or eyesockets. This placement of the eyes helps to protect them from injury.
Eyebrows
In humans, the eyebrows redirect flowing substances (usually rainwater) away from the eye. Water in the eye can alter the refractive properties of the eye and blur vision. It can also wash away the tear fluid, and its beneficial effects, and can damage the cornea, due to osmotic differences between tear fluid and freshwater.
Eyelids
In many animals, including humans, eyelids wipe the eye and prevent the eyes from dehydration. They spread tear fluid on the eyes, which contains substances which help fight bacterial infection as part of the immune system. Some aquatic animals have a second eyelid in each eye which refracts the light and helps them see clearly both above water and below it. Most creatures will automatically react to a threat to its eyes (such as an object moving straight at the eye, or a bright light) by covering the eyes, and/or by turning the eyes away from the threat. Blinking the eyes is, of course, also a reflex.
Eyelashes
In many animals, including humans, eyelashes prevent fine particles from entering the eye. Fine particles can be bacteria, but also simple dust which can cause irritation of the eye, and lead to tears and subsequent blurred vision.
Eye movement
Animals with compound eyes have a wide field of vision, allowing them to look in many directions. To see more, they have to move their entire head or even body. The visual system in the brain is too slow to process that information if the images are slipping across the retina at more than a few degrees per second (Westheimer and McKee, 1954). Thus, for humans to be able to see while moving, the brain must compensate for the motion of the head by turning the eyes. Another complication for vision in frontal-eyed animals is the development of a small area of the retina with a very high visual acuity. This area is called the fovea, and covers about 2 degrees of visual angle in people. To get a clear view of the world, the brain must turn the eyes so that the image of the object of regard falls on the fovea. Eye movements are thus very important for visual perception, and any failure to make them correctly can lead to serious visual disabilities. To see a quick demonstration of this fact, try the following experiment: hold your hand up, about one foot (30 cm) in front of your nose. Keep your head still, and shake your hand from side to side, slowly at first, and then faster and faster. At first you will be able to see your fingers quite clearly. But as the frequency of shaking passes about one hertz, the fingers will become a blur. Now, keep your hand still, and shake your head (up and down or left and right). No matter how fast you shake your head, the image of your fingers remains clear. This demonstrates that the brain can move the eyes opposite to head motion much better than it can follow, or pursue, a hand movement. When your pursuit system fails to keep up with the moving hand, images slip on the retina and you see a blurred hand. Having two eyes is an added complication, because the brain must point both of them accurately enough that the object of regard falls on corresponding points of the two retinas; otherwise, double vison would occur. The movements of different body parts are controlled by striated muscles acting around joints. The movements of the eye are no exception, but they have special advantages not shared by skeletal muscles and joints, and so are considerably different.
Extraocular muscles
Each eye has six muscles that control its movements: the lateral rectus, the medial rectus, the inferior rectus, the superior rectus, the inferior oblique, and the superior oblique. When the muscles exert different tensions, a torque is exerted on the globe that causes it to turn. This is an almost pure rotation, with only about one millimeter of translation (Carpenter, 1988). Thus, the eye can be considered as undergoing rotations about a single joint in the center of the eye.
Rapid eye movement
Rapid eye movement typically refers to the stage during sleep during which the most vivid dreams occur. During this stage, the eyes move rapidly. It is not in itself a unique form of eye movement.
Saccades
Saccades are rapid refocussing actions of the eyes. Many animals are able to quickly look at a point in space (prompted by memory, peripheral vision or an audio cue) without actively looking at anything in between. The eyes simply jerk into a new position. Saccades move the eye at up to 900°/s in adult humans.
Microsaccades
Even when looking intently at a single spot, the eyes drift around. This ensures that individual photosensitive cells are continually stimulated in different degrees. Without changing input, these cells would otherwise stop generating output. Microsaccades move the eye no more than a total of 0.2° in adult humans.
Vestibulo-ocular reflex
Many animals can look at something while turning their heads. The eyes are automatically rotated to remain fixed on the object, directed by input from the organs of balance near the ears.
Smooth pursuit movement
The eyes can also follow a moving object around. This is less accurate than the vestibulo-ocular reflex as it requires the brain to process incoming visual information and supply feedback. Following an object moving at constant speed is relatively easy, though the eyes will often make saccadic jerks to keep up. The smooth pursuit movement can move the eye at up to 100°/s in adult humans.
Optokinetic reflex
The optokinetic reflex is a combination of a saccade and smooth pursuit movement. When, for example, looking out of the window in a moving train, the eyes can focus on a 'moving' tree for a short moment (through smooth pursuit), until the tree moves out of the field of vision. At this point, the optokinetic reflex kicks in, and moves the eye back to the point where it first saw the tree (through a saccade).
Vergence movement
feedback When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of the retina in both eyes. To look at an object closer by, the eyes rotate 'towards each other' (convergence), while for an object farther away they rotate 'away from eachother' (divergence). Exaggerated convergence is called cross eyed viewing (focussing on the nose for example) . When looking into the distance, or when 'staring into nothingness', the eyes neither converge nor diverge. Vergence movements are closely connected to accommodation of the eye. Under normal conditions, changing the focus of the eyes to look at an object at a different distance will automatically cause vergence and accommodation.
Accommodation
To see clearly, the lens will be pulled flatter or allowed to regain its thicker form.
Diseases, disorders, and age-related changes
There are many diseases and disorders that may affect the eyes. As the eye ages certain changes occur that can be attributed to solely the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The area of the pupil governs the amount of light that can reach the retina. The extent to which the pupil dilates also decreases with age. Because of the smaller pupil size, older eyes receive much less light at the retina. In comparison to younger people, it is as though older persons wear medium-density sunglasses in bright light and extremely dark glasses in dim light. Therefore, for any detailed visually guided tasks on which performance varies with illumination, older person requires extra lighting. With aging a prominent white ring develops in the periphery of the cornea- called arcus senilis. Aging causes laxity and downward shift of eyelid tissues and atrophy of the orbital fat. These changes contribute to the etiology of several eyelid disorders such as ectropion, entropion, dermatochalasis,and ptosis. The vitreous gel undergoes liquefaction (posterior vitreous detachment or PVD) and its opacities - visible as floaters gradually increase in number.
See also

- WikiSaurus:eye — the WikiSaurus list of synonyms and slang words for eyes in many languages
- Adaptation
- Binocular vision
- Corrective lens
- Crystallin
- Evil eye
- Eye color
- Eye contact
- Eye tracking
- Eyeglass prescription
- Macropsia
- Micropsia
- Nictitating membrane
- Ocular tremor
- Ophthalmology
- Optician
- Optometry
- Persistence of vision
- Phosphenes
- Snellen chart
- Staring contest
- Tears
- Visual perception
External links

- [http://www.djo.harvard.edu/ DJO | Digital Journal of Ophthalmology]
- [http://www.afb.org/eyeconditions.asp Glossary of Eye Conditions]
- [http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html Evolution of the Eye]
- [http://www.eyetopics.com eye Topics]
- [http://webvision.med.utah.edu/anatomy.html Diagram of the eye]
- [http://webvision.med.utah.edu/ Webvision. The organisation of the retina and visual system.]
References

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- [http://soma.npa.uiuc.edu/courses/bio303/Ch11b.html Internet lecture on eye types in animal kindom] # [http://www.agingeye.net/ AgingEye Times] Category:Visual system Category:Head and neck Category:Ophthalmology ms:Mata ja:目 zh-min-nan:Ba̍k-chiu