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Parasol Cell
A parasol cell, sometimes called an M cell or M ganglion cell, is one type of retinal ganglion cell (RGC) located in the ganglion cell layer of the retina. These cells project to magnocellular cells in the lateral geniculate nucleus (LGN) as part of the magnocellular pathway in the visual system. They have large cell bodies as well as extensive branching dendrite networks and as such have large receptive fields. Relative to other RGCs, they have fast conduction velocities. While they do show clear center-surround antagonism (known as spatial opponency), they receive no information about color (absence of chromatic opponency). Parasol ganglion cells contribute information about the motion and depth of objects to the visual system. Parasol ganglion cells in the Magnocellular pathway Parasol ganglion cells are the first step in the magnocellular pathway of the visual system. They project from the retina via the optic nerve to the two most ventral layers of the LGN, which is a nuc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retina
The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the photographic film, film or image sensor in a camera. The neural retina consists of several layers of neurons interconnected by Chemical synapse, synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rod cell, rods and cone cell, cones. Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myelinated
Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be likened to an electrical wire (the axon) with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Myelin ensheaths part of an axon known as an internodal segment, in multiple myelin layers of a tightly regulated internodal length. The ensheathed segments are separated at regular short unmyelinated intervals, called nodes of Ranvier. Each node of Ranvier is around one micrometre long. Nodes of Ranvier enable a much faster rate of conduction known as saltatory conduction where the action potential recharges at each node to jump over to the next node, and so on till it reaches the axon terminal. At the terminal the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
In Vitro
''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and its subdisciplines are traditionally done in labware such as test tubes, flasks, Petri dishes, and microtiter plates. Studies conducted using components of an organism that have been isolated from their usual biological surroundings permit a more detailed or more convenient analysis than can be done with whole organisms; however, results obtained from ''in vitro'' experiments may not fully or accurately predict the effects on a whole organism. In contrast to ''in vitro'' experiments, ''in vivo'' studies are those conducted in living organisms, including humans, known as clinical trials, and whole plants. Definition ''In vitro'' (Latin language, Latin for "in glass"; often not italicized in English usage) studies are conducted ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frontal Lobe
The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neuroanatomy), groove between tissues called the central sulcus and from the temporal lobe by a deeper groove called the lateral sulcus (Sylvian fissure). The most anterior rounded part of the frontal lobe (though not well-defined) is known as the frontal pole, one of the three Cerebral hemisphere#Poles, poles of the cerebrum. The frontal lobe is covered by the frontal cortex. The frontal cortex includes the premotor cortex and the primary motor cortex – parts of the motor cortex. The front part of the frontal cortex is covered by the prefrontal cortex. The nonprimary motor cortex is a functionally defined portion of the frontal lobe. There are four principal Gyrus, gyri in the frontal lobe. The precentral gyrus is directly anterior to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saccade
In vision science, a saccade ( ; ; ) is a quick, simultaneous movement of both Eye movement (sensory), eyes between two or more phases of focal points in the same direction. In contrast, in Smooth pursuit, smooth-pursuit movements, the eyes move smoothly instead of in jumps. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for focal points, rapid eye movement, and the fast phase of optokinetic reflex, optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Louis Émile Javal, Émile Javal, who used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements. Function Humans and many organisms do not look at a scene in steadiness; instead, the eyes move around, locating interesting parts of the scene and building up a three-dimensional 'map' corresponding to the scen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intraparietal Sulcus
The intraparietal sulcus (IPS) is located on the lateral surface of the parietal lobe, and consists of an oblique and a horizontal portion. The IPS contains a series of functionally distinct subregions that have been intensively investigated using both single cell neurophysiology in primates and human functional neuroimaging. Its principal functions are related to perceptual-motor coordination (e.g., directing eye movements and reaching) and visual attention, which allows for visually-guided pointing, grasping, and object manipulation that can produce a desired effect. The intraparietal sulcus (IPS) plays a pivotal role in multisensory integration, particularly in linking visual and tactile information to guide complex motor actions. Beyond its established roles in numerical cognition and spatial attention, the IPS has emerged as a critical player in tool use and manipulation. The IPS is also thought to play a role in other functions, including processing symbolic numerical infor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Depth Perception
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 sensation is the corresponding term for non-human animals, since although it is known that they can sense the distance of an object, it is not known whether they perceive it in the same way that humans do. Depth perception arises from a variety of depth cues. These are typically classified into binocular cues and monocular cues. Binocular cues are based on the receipt of sensory information in three dimensions from both eyes and monocular cues can be observed with just one eye. Binocular cues include retinal disparity, which exploits parallax and vergence. Stereopsis is made possible with binocular vision. Monocular cues include relative size (distant objects subtend smaller visual angles than near objects), texture gradient, occlusion, linear perspective, contrast differences, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Search
Visual search is a type of perception, perceptual task requiring attention that typically involves an active scan of the visual environment for a particular object or feature (the target) among other objects or features (the distractors). Visual search can take place with or without eye movements. The ability to consciously locate an object or target amongst a complex array of stimuli has been extensively studied over the past 40 years. Practical examples of using visual search can be seen in everyday life, such as when one is picking out a product on a supermarket shelf, when animals are searching for food among piles of leaves, when trying to find a friend in a large crowd of people, or simply when playing visual search games such as ''Where's Wally?'' Much previous literature on visual search used reaction time in order to measure the time it takes to detect the target amongst its distractors. An example of this could be a green square (the target) amongst a set of red circles ( ... [...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] |
Spatial Frequency
In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier transform) of the structure repeat per unit of distance. The SI unit of spatial frequency is the reciprocal metre (m−1), (11 pages) although cycle (rotational unit), cycles per (c/m) is also common. In image-processing applications, spatial freque ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fovea Centralis
The ''fovea centralis'' is a small, central pit composed of closely packed Cone cell, cones in the eye. It is located in the center of the ''macula lutea'' of the retina. The ''fovea'' is responsible for sharp central visual perception, vision (also called foveal vision), which is necessary in humans for activities for which visual detail is of primary importance, such as reading (activity), reading and driving. The fovea is surrounded by the ''parafovea'' belt and the ''perifovea'' outer region. The ''parafovea'' is the intermediate belt, where the Retinal ganglion cell, ganglion cell layer is composed of more than five layers of cells, as well as the highest density of cones; the ''perifovea'' is the outermost region where the ganglion cell layer contains two to four layers of cells, and is where visual acuity is below the optimum. The ''perifovea'' contains an even more diminished density of cones, having 12 per 100 micrometres versus 50 per 100 micrometres in the most centra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cone Cell
Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most vertebrates (including humans) have several classes of cones, each sensitive to a different part of the visible spectrum of light. The comparison of the responses of different cone cell classes enables color vision. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration occurring towards the macula and most densely packed in the fovea centralis, a diameter rod-free area with very thin, densely packed cones. Conversely, like rods, they are absent from the optic disc, contributing to the blind spot. Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
