In visual perception, an optical illusion is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect. An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.
Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth perception happens primarily due to stereopsis and accommodation of the eye.
Anti-gravity is a hypothetical phenomenon of creating a place or object that is free from the force of gravity. It does not refer to either the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism and aerodynamic lift. Anti-gravity is a recurring concept in science fiction. Examples are the gravity blocking substance "Cavorite" in H. G. Wells's The First Men in the Moon and the Spindizzy machines in James Blish's Cities in Flight.
Whiteout, white-out, or milky weather is a weather condition in which the contours and landmarks in a snow-covered zone become almost indistinguishable. It could be also applied when visibility and contours are greatly reduced by sand. The horizon disappears from view while the sky and landscape appear featureless, leaving no points of visual reference by which to navigate; there is absence of shadows because the light arrives in equal measure from all possible directions. Whiteout has been defined as: "A condition of diffuse light when no shadows are cast, due to a continuous white cloud layer appearing to merge with the white snow surface. No surface irregularities of the snow are visible, but a dark object may be clearly seen. There is no visible horizon."
The Oregon Vortex is a roadside attraction that opened to tourists in 1930, located on Sardine Creek in Gold Hill, Oregon, in the United States. It consists of a number of interesting effects, which are gravity hill optical illusions, but which the attraction's proprietors propose are the result of paranormal properties of the area.
Spatial disorientation is the inability to determine position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibular system, and proprioceptive system collectively work to coordinate movement with balance, and can also create illusory nonvisual sensations, resulting in spatial disorientation in the absence of strong visual cues.
An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction. It is also known as a tilt indicator, tilt sensor, tilt meter, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, declinometer, and pitch & roll indicator. Clinometers measure both inclines and declines using three different units of measure: degrees, percentage points, and topos. The astrolabe is an example of an inclinometer that was used for celestial navigation and location of astronomical objects from ancient times to the Renaissance.
The Moon illusion is an optical illusion which causes the Moon to appear larger near the horizon than it does higher up in the sky. It has been known since ancient times and recorded by various cultures. The explanation of this illusion is still debated.
The Mystery Spot is a tourist attraction near Santa Cruz, California, opened in 1939 by George Prather. Visitors experience demonstrations that appear to defy gravity, on the short but steep uphill walk and inside a wooden building on the site. It is a popular tourist attraction, and gained recognition as a roadside "gravity box" or "tilted house". The site is what is known as a gravity hill and was the first of its kind to be built in California.
An Ames room is a distorted room that creates an optical illusion. Likely influenced by the writings of Hermann Helmholtz, it was invented by American scientist Adelbert Ames Jr. in 1946, and constructed in the following year.
The Electric Brae is a gravity hill in South Ayrshire, Scotland, where a freewheeling vehicle will appear to be drawn uphill by some mysterious attraction. The phenomenon is an optical illusion.
Polo is a municipality of the Barahona Province in southwestern Dominican Republic, known for its green and high mountains and for growing fine coffee.
Human senses are not naturally geared for the in-flight environment. Pilots may experience disorientation and loss of perspective, creating illusions that range from false horizons to sensory conflict with instrument readings or the misjudging of altitude over water.
Magnet Hill is a gravity hill located, near Leh in Leh district of Ladakh, India. The layout of the area and surrounding slopes create the optical illusion of a hill. The hill road is actually a downhill road. Objects and cars on the hill road may appear to roll uphill in defiance of gravity when they are, in fact, rolling downhill. It is 7.5 km southeast of Nimmoo and 26.5 km west of Leh on Srinagar-Leh road.
Nimo or Nyemo is a village and the headquarters of an eponymous community development block in the Leh district of Ladakh, India. It is located in the Leh tehsil, 35 km from Leh.
Tulsishyam is located on the border of Amareli, Junagadh district and Gir Somnath district, in the Gir National Park in Gujarat state of India. It reachable by road 45 km from Dhari in Amreli district and 35 km from Una in Gir Somnath district. Ruled by the Kotilas's of Dedan ,last ruler was kumarshree Jilubapu Kotila. Successor of kumarshree Jilubapu Kotila is Kumarshree Pratapbapu kotila. The son of kumarshree Pratapbapu kotila is Prince Nandkishor kotila.
Kalo Dungar or Black Hill is the highest point in Kutch, Gujarat, India, at 462 m (1,516 ft). It is located 97 km (60 mi) from District headquarters of Bhuj and 25 km (16 mi) from nearest town Khavda.
Kimanis–Keningau Highway is a state highway in Sabah, Malaysia, connecting the town of Kimanis to Keningau. It also acts as an alternative for Federal Route 500 from Kota Kinabalu to Tenom which is nowadays somewhat under-use. The 53-kilometre (33 mi) highway began as a main logging road before being upgraded to a full two-lane highway. The highway was opened to traffic in 2006.
Scray Hill is an 892-foot (272 m) summit in Brown County, Wisconsin, at 44°24′58″N87°59′48″W. Located just south of De Pere, much of the hill is in the Town of Glenmore; some of its northwestern edges are in the Town of Ledgeview. Scray Hill is home to many television, radio, and communications towers and transmitters, as well as the Central Brown County Water Authority (CBCWA) storage facility.
