An afterimage is an optical illusion that occurs after looking away from a direct gaze at an image. This is closely related to the phenomenon called the persistence of vision, which is used in animation and cinema. One of the most common afterimages is the bright glow that seems to float before one's eyes after staring at a light bulb or a headlight for a few seconds. ...more on Wikipedia about "Afterimage"
Anomalous trichromacy, or anomalous trichromatism, is a common type of congenital color vision deficiency caused by a reduced amount (not absence) of one of the three types of cone pigments ** . ...more on Wikipedia about "Anomalous trichromacy"
In optics, astigmatism is a monochromatic aberration in which an optical system has different focal planes for rays in different planes. Lenses and mirrors which are partly cylindrical show this behaviour already for on-axis rays, parabolic mirrors and uncorrected lens systems only proportional to the squared angle between rays and optical axis. Optical systems which are corrected to have no, or only higher order, astigmatism are called anastigmats. ...more on Wikipedia about "Astigmatism"
The autokinetic effect is a phenomenon of human visual perception in which a stationary, small point of light in an otherwise dark or featureless environment appears to move. It was first recorded by a Russian officer keeping watch who observed illusory movement of a star near the horizon. It presumably occurs because motion perception is always relative to some reference point. In darkness or in a featureless environment there is no reference point, so the movement of the single point is undefined. The direction of the movements does not appear to be correlated with the involuntary eye movements, but may be determined by errors between eye position and that specified by efference copy of the movement signals sent to the extraocular muscles. ...more on Wikipedia about "Autokinetic effect"
Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each eye. When one image is presented to one eye and a very different image is presented to the other, instead of the two images being seen superimposed, one image is seen for a few moments, then the other, then the first, and so on, randomly for as long as one cares to look. For example if a set of vertical lines is presented to one eye, and a set of horizontal lines to the same region of the retina of the other, sometimes the vertical lines are seen with no trace of the horizontal lines, and sometimes the horizontal lines are seen with no trace of the vertical lines. At transitions, brief, unstable composites of the two images may be seen; these are often organized. For example, the vertical lines may appear one at a time to obscure the horizontal lines from the left or from the right, or the horizontal lines make appear one at a time to obscure the vertical lines from the top or from the bottom. Binocular rivalry occurs between any stimuli that differ sufficiently, including simple stimuli like lines of different orientation and complex stimuli like different alphabetic letters or different pictures such as of a face and of a house. Very small differences between images, however, might yield singleness of vision and stereopsis. In recent years neuroscientists have used neuroimaging techniques and single-cell recording techniques to identify neural events responsible for the perceptual dominance of a given image and for the perceptual alternations. ...more on Wikipedia about "Binocular rivalry"
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bin for two, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a wider field of view. For example, a human has a horizontal field of view with one eye of about 150 degrees and with two eyes of about 180 degrees. Third, it gives binocular summation in which the ability to detect faint objects is enhanced. Fourth it can give stereopsis in which parallax provided by the two eyes' different positions on the head give precise depth perception. Such binocular vision is usually accompanied by singleness of vision or binocular fusion, in which a single image is seen despite each eye's having its own image of any object. ...more on Wikipedia about "Binocular vision"
In anatomy, the blind spot is the region of the retina where the optic nerve and blood vessels pass through to connect to the back of the eye. Since there are no light receptors there, a part of the field of vision is not perceived. The brain fills in with surrounding detail and with information from the other eye, so the blind spot is not normally perceived. ...more on Wikipedia about "Blind spot (anatomy)"
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Although individuals with damage to V1 are not consciously aware of stimuli presented in their blind field, Larry Weiskrantz and colleagues showed in the early 1970s that if forced to guess about whether a stimulus is present in their blind field, they do rather better than chance. This ability to detect stimuli that the individual is not aware of can extend to discrimination of the type of stimulus (for example, whether an 'X' or 'O' has been presented in the blind field), and has been dubbed blindsight. ...more on Wikipedia about "Blindsight"
The blue field entoptic phenomenon or Scheerer's phenomenon is the appearance of tiny bright dots moving quickly along squiggly lines in the visual field, especially when looking into blue light (such as the sky). ...more on Wikipedia about "Blue field entoptic phenomenon"
Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. In other words, brightness is the perception elicited by the luminance of a visual target. ...more on Wikipedia about "Brightness"
In the study of the perception of color, one of the first mathematically defined color spaces was the CIE XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931. ...more on Wikipedia about "CIE 1931 color space"
Color or colour is the perception of the frequency (or wavelength) of light, and can be compared to how pitch (or a musical note) is the perception of the frequency or wavelength of sound. ...more on Wikipedia about "Color"
Color blindness, or color vision deficiency, in humans is the inability to perceive differences between some or all colors that other people can distinguish. It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals. The English chemist John Dalton in 1794 published the first scientific paper on the subject, "Extraordinary facts relating to the vision of colors", after the realization of his own color blindness; because of Dalton's work, the condition is sometimes called Daltonism, although this term is now used for a type of color blindness called deuteranopia (see below). ...more on Wikipedia about "Color blindness"
A color circle is a way of representing the visible spectrum in a circular form, with colors arranged in sequence around the circumference in order of spectral frequency. Analogous to the use of a color wheel in art, the color circle performs a different purpose, as it is a psychophysical tool used in the exploration of visual perception, its anomalies and optical illusions connected with color vision. ...more on Wikipedia about "Color circle"
Color constancy is an example of subjective constancy and a feature of the human color-perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. An apple for instance looks green to us at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red. This helps us identify objects. Some nonhuman species, such as monkeys and goldfish have also been shown to have color constancy. It is likely that all animals with color vision have color constancy. ...more on Wikipedia about "Color constancy"
Color vision is the capacity of an organism or machine to distinguish objects based on the wavelength of the light they reflect or emit. A 'red' apple does not emit red light. Rather, it simply absorbs all the frequencies of light shining on it except the frequencies we call red, which are reflected. An apple is perceived to be red only because the human eye can distinguish between different wavelengths—and we have language to describe that difference. Three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view. ...more on Wikipedia about "Color vision"
Contrast has several meanings: ...more on Wikipedia about "Contrast"
Cortical magnification describes how many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size, as a function of visual field location. In the center of the visual field, corresponding to the fovea of the retina, a very large number of neurons process information from a small region of the visual field. If the same stimulus is seen in the periphery of the visual field (i.e. away from the center), it would be processed by a much smaller number of neurons. The reduction of the number of neurons per visual field area is achieved in several steps along the visual pathway, starting already in the retina. ...more on Wikipedia about "Cortical magnification"
Cosmic rays were first reported to cause visual perception of flashes of light during the Apollo program. Astronauts en route for the Moon were subject to cosmic ray bombardments, and it is believed that these rays produced Cherenkov radiation as they passed through the vitreous humor of the astronauts' eyeballs. ...more on Wikipedia about "Cosmic ray visual phenomena"
Depth perception is the visual ability to perceive the world in three dimensions. It is a trait common to many higher animals. Depth perception allows the beholder to accurately gauge the distance to an object. ...more on Wikipedia about "Depth perception"
A dichromat is an organism that can match any color they see with a mixture of no more than two pure spectral lights. By comparison, a trichromat requires three pure spectral lights to match all colors in their visual spectrum. The condition of being a dichromat is called dichromacy. ...more on Wikipedia about "Dichromat"
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Entoptic phenomena are visual effects whose source is within the eye itself. ...more on Wikipedia about "Entoptic phenomenon"
(Eye injury) Tiny metallic projectiles should be suspected when a patient reports metal on metal contact, such as with hammering a metal surface. ...more on Wikipedia about "Eye injury"
An eye tracker is a device for measuring eye positions and eye movements. The most popular variant uses video images from which the eye position is extracted. Other methods use search coils or are based on the electrooculogram. ...more on Wikipedia about "Eye tracker"
Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face. ...more on Wikipedia about "Face perception" http://www.shortopedia.com, the smart choice.
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