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Vernier Acuity
Vernier acuity (from the term "vernier scale", named after astronomer Pierre Vernier) is a type of visual acuity – more precisely of hyperacuity – that measures the ability to discern a disalignment among two line segments or gratings. A subject's vernier (IPA: ) acuity is the smallest visible offset between the stimuli that can be detected. Because the disalignments are often much smaller than the diameter and spacing of retinal ganglion cell, retinal receptors, vernier acuity requires neural processing and "pooling" to detect it. Because vernier acuity exceeds acuity by far, the phenomenon has been termed hyperacuity. Vernier acuity develops rapidly during infancy and continues to slowly develop throughout childhood. At approximately three to twelve months old, it surpasses grating acuity in Fovea centralis, foveal vision in humans. However, vernier acuity decreases more quickly than grating acuity in peripheral vision. Vernier acuity was first explained by Ewald Hering in 1899 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle. The procedure for conversion from spectral radiance to luminance is standardized by the CIE and ISO. Brightness is the term for the ''subjective'' impression of the ''objective'' luminance measurement standard (see for the importance of this contrast). The SI unit for luminance is candela per square metre (cd/m2). A non-SI term for the same unit is the nit. The unit in the Centimetre–gram–second system of units (CGS) (which predated the SI system) is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2. Description Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. Luminance levels indicate how much luminous power could be det ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Snellen Chart
A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula developed by his professor Franciscus_Donders, Franciscus Cornelius Donders. Many ophthalmologists and vision scientists now use an improved chart known as the LogMAR chart. History Snellen developed charts using symbols based in a 5×5 unit grid. The experimental charts developed in 1861 used abstract symbols. Snellen's charts published in 1862 used alphanumeric capitals in the 5×5 grid. The original chart shows A, C, E, G, L, N, P, R, T, 5, V, Z, B, D, 4, F, H, K, O, S, 3, U, Y, A, C, E, G, L, 2. Description The normal Snellen chart is printed with eleven lines of block letters. The first line consists of one very large letter, which may be one of several letters, for example E, H, or N. Subsequent rows have increasing numbers of letters that decrease in s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereoscopic Acuity
Stereoscopic acuity, also stereoacuity, is the smallest detectable depth difference that can be seen in binocular vision. Specification and measurement Stereoacuity is most simply explained by considering one of its earliest test, a two-peg device, named Howard-Dolman test after its inventors: The observer is shown a black peg at a distance of 6m (=20 feet). A second peg, below it, can be moved back and forth until it is just detectably nearer than the fixed one. Stereoacuity is defined as the minimum angle detectable, calculated as the difference between the angles subtended by both positions, A and B. Stereoacuity is possible due to binocular disparity, i.e., the difference in their binocular parallax. Taking into account that a small angle expressed in radians can be approximated by its tangent, the formula to calculate stereoacuity ''dγ'' is this: :d\gamma = c\,a\,dz/(z\,(z - dz)) where ''a'' is the interocular separation of the observer, ''z'' the distance of the fixed peg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vernier Scale
A vernier scale ( ), named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, which increases resolution and reduces measurement uncertainty by using vernier acuity. It may be found on many types of instrument measuring length or measuring angles, but in particular on a vernier caliper, which measures lengths of human-scale objects (including internal and external diameters). The vernier is a subsidiary scale replacing a single measured-value pointer, and has for instance ten divisions equal in distance to nine divisions on the main scale. The interpolated reading is obtained by observing which of the vernier scale graduations is coincident with a graduation on the main scale, which is easier to perceive than visual estimation between two points. Such an arrangement can go to a higher resolution by using a higher scale ratio, known as the vernier constant. A ver ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monocular Vision
Monocular vision is vision using only one eye. It is seen in two distinct categories: either a species moves its eyes independently, or a species typically uses two eyes for vision, but is unable to use one due to circumstances such as injury. Monocular vision can occur in both humans and animals (such as hammerhead sharks). Humans can benefit from several monocular cues when using only one eye, such as motion parallax and perspective. There are also some mythological creatures with only one eye, such as the cyclops. In human species Monocular vision is known as seeing and using only one eye in the human species. Depth perception in monocular vision is reduced compared to binocular vision, but still is active primarily due to accommodation of the eye and motion parallax. The word monocular comes from the Greek root, ''mono'' for single, and the Latin root, ''oculus'' for eye. In animals The eyes of an animal with monocular vision are positioned on opposite sides of the animal' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binocular Vision
Binocular vision is seeing with two eyes. The Field_of_view, field of view that can be surveyed with two eyes is greater than with one eye. To the extent that the visual fields of the two eyes overlap, #Depth, binocular depth can be perceived. This allows objects to be recognized more quickly, camouflage to be detected, spatial relationships to be perceived more quickly and accurately (#Stereopsis, stereopsis) and perception to be less susceptible to optical illusions, optical illusions. In secion #Medical, Medical attention is paid to the occurrence, defects and sharpness of binocular vision. In section #Biological, Biological the occurrence of binocular vision in animals is described. Geometric terms When the left eye (LE) and the right eye (RE) observe two objects X and Y, the following concepts are important:Krol J.D.(1982),"Perceptual ghosts in stereopsis, a ghosly problem in binocular vision", PhD thesis ISBN 90-9000382-7.Koenderink J.J.;van Doorn A.J. (1976) "Geometry of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Absolute Threshold
In neuroscience and psychophysics, an absolute threshold was originally defined as the lowest level of a stimulus – light, sound, touch, etc. – that an organism could detect. Under the influence of signal detection theory, absolute threshold has been redefined as the level at which a stimulus will be detected a specified percentage (often 50%) of the time. The absolute threshold can be influenced by several different factors, such as the subject's motivations and expectations, cognitive processes, and whether the subject is adapted to the stimulus.Absolute Threshold." Gale Encyclopedia of Psychology. 2001. Retrieved 14 July 2010 from Encyclopedia.com The absolute threshold can be compared to the [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attention
Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James (1890) wrote that "Attention is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence." Attention has also been described as the allocation of limited cognitive processing resources. Attention is manifested by an attentional bottleneck, in terms of the amount of data the brain can process each second; for example, in human vision, less than 1% of the visual input data stream of 1MByte/sec can enter the bottleneck, leading to inattentional blindness. Attention remains a crucial area of investigation within education, psychology, neuroscience, cognitive neuroscience, and neuropsychology. Areas of activ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alfred Wilhelm Volkmann
Alfred Wilhelm Volkmann (; 1 July 1801 – 21 April 1877) was a German physiologist, anatomist, and philosopher. He specialized in the study of the nervous and optic system. Biography Alfred Wilhelm Volkmann was born in Leipzig, and enrolled in medicine there in 1821. Together with Gustav Theodor Fechner, who got his degree in medicine in 1822, and Rudolph Hermann Lotze (1817–1881), they formed a small intellectual group which dissolved only in 1837 when Volkmann received his professorship in Dorpat (now Tartu). In 1826 he obtained his doctorate and in 1828 he was habilitated as ''Privatdozent'' at the University of Leipzig. It was there that he became professor extraordinary of zootomy in 1834. In 1837 he went to Dorpat as professor of physiology, pathology and semiotics. However, his residence in Dorpat was short: he left for Halle as early as 1843. After moving to Halle, Volkmann helped Gustav Theodor Fechner, his brother-in-law (married to Volkmann's sister Clara Fechner) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vernier Scale
A vernier scale ( ), named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, which increases resolution and reduces measurement uncertainty by using vernier acuity. It may be found on many types of instrument measuring length or measuring angles, but in particular on a vernier caliper, which measures lengths of human-scale objects (including internal and external diameters). The vernier is a subsidiary scale replacing a single measured-value pointer, and has for instance ten divisions equal in distance to nine divisions on the main scale. The interpolated reading is obtained by observing which of the vernier scale graduations is coincident with a graduation on the main scale, which is easier to perceive than visual estimation between two points. Such an arrangement can go to a higher resolution by using a higher scale ratio, known as the vernier constant. A ver ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ewald Hering
Karl Ewald Konstantin Hering (5 August 1834 – 26 January 1918) was a German physiologist who did much research in color vision, binocular perception, eye movements, and hyperacuity. He proposed opponent color theory in 1892. Born in Gersdorf, Saxony, Alt-Gersdorf, Kingdom of Saxony, Hering studied at the University of Leipzig and became the first rector of the Karl-Ferdinands-Universität, German Charles-Ferdinand University in Prague. Biography Early years Hering was born in Alt-Gersdorf in Saxony, Germany. He probably grew up in a poor family, son of a Lutheran pastor. Hering attended gymnasium in Zittau and entered the university of Leipzig in 1853. There he studied philosophy, zoology and medicine. He completed an M.D. degree in 1860. It is somewhat unclear how Hering trained to do research. At the time Johannes Peter Müller was perhaps the most famous physiologist in Germany. Hering seems to have applied for studying under his direction but was rejected, which m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
