The ability to interpret visible light information reaching the eyes is called visual perception. Sight is the resulting perception. The components that are necessary for vision are known as the visual system.
Light enters the animal's eyes, and a part of the eye called the lens sends information from the light to the back part of the eye called the retina. The retina is composed of light-sensitive cells which fire a signal down the optic nerve when light hits the cell. The optic nerve is a bundle of nerve fibres from all over the retina.
When the information from the light leaves the retina, it goes to the brain. It travels along the optic chiasma until it reaches the optic cortex at the rear of the brain. The information is then processed to find out the shapes and colours of objects. From that and from memory, it can tell of what kind the object is. For example, it can somehow tell a tree from a house. The path on which this kind of information flows is called "ventral stream".
The brain can also tell where objects are. For example, it can tell how far away an object is (this is called depth perception). This is needed when catching a ball. The path on which this kind of information flows is called "dorsal stream".
The major problem in visual perception is that what people see is not simply a translation of an image on the retina. For one thing, we see the world right side up, even though the image on the retina is upside down (because it has passed through the lens). Therefore, it is difficult to explain what happens to create what we actually see. The key, which took centuries to be appreciated, is that the brain works on the data from the eyes, and marries it with memories and guesses, all at lightning speed. The result is an experience of the world which looks to each person as if it were simple reality. However, although based on reality, it is actually a mental construct, built by the brain.
Many figures in the ancient world had ideas about vision. Plato, Aristotle, Euclid, Ptolemy and Galen all had their ideas, but most of these ideas were speculation. They were not based on any scientific method.
Alhazen (965–c. 1040) carried out investigations and experiments on visual perception. He extended the work of Ptolemy on binocular vision, and commented on the anatomical works of Galen.
Leonardo da Vinci (1452–1519) is believed to be the first to recognize the special optical qualities of the eye. He wrote "The function of the human eye ... was described by a large number of authors in a certain way. But I found it to be completely different". His main experimental finding was that there is only a distinct and clear vision at the line of sight, the optical line that ends at the fovea. Although he did not use these words literally he actually is the father of the modern distinction between foveal and peripheral vision.
Hermann von Helmholtz examined the human eye and concluded that it was, optically, rather poor. The poor-quality information gathered by the eye seemed to him to make vision impossible. So he thought vision could only be the result of some form of unconscious inferences. As well as information from the eyes, the brain used information from previous experiences. The world as experienced is built up from assumptions and conclusions from incomplete data, using prior experience of the world.
Examples of well-known assumptions, based on visual experience, are:
The study of visual illusions (cases when the inference process goes wrong) has yielded much insight into what sort of assumptions the visual system makes.
Pharynx
The pharynx is an organ in the back of the throat. It is also the meeting point of the digestive and the respiratory systems. The opening of the respiratory system in the pharynx is called the glottis. It is guarded by a cartilagenous flap called the epiglottis which prevents food or liquid from going into the respiratory system. It closes during swallowing action. As such, it is part of the gastrointestinal system. It comes after the mouth and before the esophagus. Food and air go through the pharynx. The pharynx keeps food and liquids out of the lungs.
The pharynx has 3 parts:
Jejunum
The jejunum is a section of the small intestine between the duodenum and the ileum. It is between 1 and 2 meters long.The term "jejunum" derives from the Latin "jejunus," which means "empty of food," "meager," or "hungry." The ancient Greeks noticed at death that this part of the intestine was always empty of food. Hence, the name the jejunum.
The Latin "jejunus" also gave rise to "jejune" means lacking in nutritive value and devoid of substance, significance or interest, that is dull. A jejune argument is one that is empty (like the jejunum) and totally devoid of interest.
Famous quote..."Have You Ever Been Punched in The Jejunum?"
Ileum
The ileum is the last section of the small intestine. It is between 2 and 4 meters long in humans.
Cecum
The cecum is a part of the large intestine. It helps with fermenting dietary fiber. It comes before the colon and after the ileum in the gastrointestinal system. The appendix is connected to the cecum. The size of the cecum varies in humans and other omnivores but it is large in herbivores and small in most carnivores.
Romano Prodi
Romano Prodi (born 9 August 1939 in Scandiano, Italy) is an Italian politician and leader of a left-wing coalition named "L'unione" (The Union).
Prodi was "President of the Council of Ministers", that is, Prime Minister of Italy between 1996 and 1998.
He then served as President of the European Commission from 1999 to 2004.
He was re-elected Prime Minister of Italy for a second time in 2006, when he defeated Silvio Berlusconi, leader of the right-wing coalition named "Casa delle Libertà" (House of Freedom).
2013
2013 (MMXIII) was . It was the first year since 1987 to have all four of its digits being different numbers.
Basilicata
Basilicata is a region in the south of Italy. The capital is Potenza. The population was about 597,768 in 2004. The region is very mountainous. Because of this, communication in the area was very difficult until modern times. This has also caused Basilicata to be one of the least developed areas of Italy. Basilicata borders the Tyrrhenian Sea and the Gulf of Taranto at its lowest elevations. The highest point in the area is Monte Pollino at 2233m (7325ft). The area also includes a dead volcano, Monte Vulture. The region has an area of .
Basilicata also used to be one of the poorest regions in Italy. It has become richer over the past couple of years because of the discovery of oil.
Basilicata is divided into two provinces.
Campania
Campania is a region of the south of Italy. The capital is Napoli. The population in 2004 was about 5,701,931.
Emilia-Romagna
Emilia-Romagna (Emilian: "Emégglia-Rumâgna", "Emîlia-Rumâgna", Romagnol: "Emélia-Rumâgna") is one of the twenty regions of Italy, in northeast Italy on the Adriatic Sea. The capital is Bologna.
The region is in Northern Italy with an area of . It is bordered to the north by the Veneto and Lombardy regions, to the northwest by the Piedmont and Liguria regions, to the west by the Tuscany, to the south by the Marche region and the republic of San Marino, and the Adriatic Sea to the east.
The main river in the region is the Po. The highest mountain in the region is Monte Cimone, in the northern Apennines, with an altitude of .
Emilia-Romagna has nine provinces grouped in two historical regions:
The 10 communi with more people living in it are:
Vasil Levski
Vasil Levski is a Bulgarian hero. He was born in Karlovo, Bulgaria in 1837. His real name is Vasil Ivanov Kuncev and "Levski" was his nickname. His father's name was Ivan Kuncev. Vasil Levski struggled for independence of Bulgaria from the Ottoman Empire. He was executed in 1873.
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