Visual system in the context of Web content

Perception (from Latin perceptio 'gathering, receiving') is the organization, identification, and interpretation of sensory information, in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system, which in turn result from physical or chemical stimulation of the sensory system. Vision involves light striking the retina of the eye; smell is mediated by odor molecules; and hearing involves pressure waves.

Perception is not only the passive receipt of these signals, but it is also shaped by the recipient's learning, memory, expectation, and attention. Sensory input is a process that transforms this low-level information to higher-level information (e.g., extracts shapes for object recognition). The following process connects a person's concepts and expectations (or knowledge) with restorative and selective mechanisms, such as attention, that influence perception.

In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication channel or storage in a storage medium. An early example is an invention of language, which enabled a person, through speech, to communicate what they thought, saw, heard, or felt to others. But speech limits the range of communication to the distance a voice can carry and limits the audience to those present when the speech is uttered. The invention of writing, which converted spoken language into visual symbols, extended the range of communication across space and time.

The process of encoding converts information from a source into symbols for communication or storage. Decoding is the reverse process, converting code symbols back into a form that the recipient understands, such as English, Spanish, etc.

In the study of the biological sciences, biocommunication is any specific type of communication within (intraspecific) or between (interspecific) species of plants, animals, fungi, protozoa and microorganisms. Communication means sign-mediated interactions following three levels of rules (syntactic, pragmatic and semantic). Signs in most cases are chemical molecules (semiochemicals), but also tactile, or as in animals also visual and auditive. Biocommunication of animals may include vocalizations (as between competing bird species), or pheromone production (as between various species of insects), chemical signals between plants and animals (as in tannin production used by vascular plants to warn away insects), and chemically mediated communication between plants and within plants.

Biocommunication of fungi demonstrates that mycelia communication integrates interspecific sign-mediated interactions between fungal organisms, soil bacteria and plant root cells without which plant nutrition could not be organized. Biocommunication of Ciliates identifies the various levels and motifs of communication in these unicellular eukaryotes. Biocommunication of Archaea represents key levels of sign-mediated interactions in the evolutionarily oldest akaryotes. Biocommunication of phages demonstrates that the most abundant living agents on this planet coordinate and organize by sign-mediated interactions. Biocommunication is the essential tool to coordinate behavior of various cell types of immune systems.

Elaborative encoding is a mnemonic system that uses some form of elaboration, such as an emotional cue, to assist in the retention of memories and knowledge. In this system one attaches an additional piece of information to a memory task which makes it easier to recall. For instance, one may recognize a face easier if character traits are also imparted about the person at the same time.

Practitioners use multiple techniques, such as the method of loci, the link system, the peg-word method, PAO (person, action, object), etc., to store information in long-term memory and to make it easier to recall this information in the future. One can make such connections visually, spatially, semantically or acoustically.

Color vision (CV), a feature of visual perception, is an ability to perceive differences between light composed of different frequencies independently of light intensity.

Color perception is a part of the larger visual system and is mediated by a complex process between neurons that begins with differential stimulation of different types of photoreceptors by light entering the eye. Those photoreceptors then emit outputs that are propagated through many layers of neurons ultimately leading to higher cognitive functions in the brain. Color vision is found in many animals and is mediated by similar underlying mechanisms with common types of biological molecules and a complex history of the evolution of color vision within different animal taxa. In primates, color vision may have evolved under selective pressure for a variety of visual tasks including the foraging for nutritious young leaves, ripe fruit, and flowers, as well as detecting predator camouflage and emotional states in other primates.

The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved in sensory perception and interoception. Commonly recognized sensory systems are those for vision, hearing, touch, taste, smell, balance and visceral sensation. Sense organs are transducers that convert data from the outer physical world to the realm of the mind where people interpret the information, creating their perception of the world around them.

The receptive field is the area of the body or environment to which a receptor organ and receptor cells respond. For instance, the part of the world an eye can see, is its receptive field; the light that each rod or cone can see, is its receptive field. Receptive fields have been identified for the visual system, auditory system and somatosensory system.

Visual perception is the ability to detect light and use it to form an image of the surrounding environment. Photodetection without image formation is classified as light sensing. In most vertebrates, visual perception can be enabled by photopic vision (daytime vision) or scotopic vision (night vision), with most vertebrates having both. Visual perception detects light (photons) in the visible spectrum reflected by objects in the environment or emitted by light sources. The visible range of light is defined by what is readily perceptible to humans, though the visual perception of non-humans often extends beyond the visual spectrum. The resulting perception is also known as vision, sight, or eyesight (adjectives visual, optical, and ocular, respectively). The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in linguistics, psychology, cognitive science, neuroscience, and molecular biology, collectively referred to as vision science.

The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and keeping balance.

The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye (the sclera) and one of its inner layers (the pigmented choroid) keeping the eye essentially light tight except on the eye's optic axis. In order, along the optic axis, the optical components consist of a first lens (the cornea—the clear part of the eye) that accounts for most of the optical power of the eye and accomplishes most of the focusing of light from the outside world; then an aperture (the pupil) in a diaphragm (the iris—the coloured part of the eye), which controls the amount of light entering the interior of the eye; then another lens (the crystalline lens) that accomplishes the remaining focusing of light into images; and finally a light-sensitive part of the eye (the retina), where the images fall and are processed. The retina makes a connection to the brain via the optic nerve. The remaining components of the eye keep it in its required shape, nourish and maintain it, and protect it.

Vergence-accommodation conflict (VAC), also known as accommodation-vergence conflict, is a visual phenomenon that occurs when the brain receives mismatching cues between vergence and accommodation of the eye. This commonly occurs in virtual reality devices, augmented reality devices, 3D movies, and other types of stereoscopic displays and autostereoscopic displays. The effect can be unpleasant and cause eye strain.

Two main ocular responses can be distinguished: vergence of eyes, and accommodation. Both of these mechanisms are crucial in stereoscopic vision. Vergence or independent inward/outward rotation of eyes is engaged to fixate on objects and perceive them as single. Incorrect vergence response can cause double vision. Accommodation is the eye's focusing mechanism and it is engaged to produce a sharp image on a retina. Both of these mechanisms are neurally linked forming the accommodation-convergence reflex of eyes. One can distinguish vergence distance‍—‍a distance of a point towards which both eyes are converging, and an accommodation distance‍—‍a distance of a region in space towards which the focus or refractive power of the crystalline lens has been adjusted to produce a sharp image on the retina.

A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential.

There are currently three known types of photoreceptor cells in mammalian eyes: rods, cones, and intrinsically photosensitive retinal ganglion cells. The two classic photoreceptor cells are rods and cones, each contributing information used by the visual system to form an image of the environment, sight. Rods primarily mediate scotopic vision (dim conditions) whereas cones primarily mediate photopic vision (bright conditions), but the processes in each that supports phototransduction is similar. The intrinsically photosensitive retinal ganglion cells were discovered during the 1990s. These cells are thought not to contribute to sight directly, but have a role in the entrainment of the circadian rhythm and the pupillary reflex.

An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system.

In higher organisms, the eye is a complex optical system that collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain.

Scientific modelling is an activity that produces models representing empirical objects, phenomena, and physical processes, to make a particular part or feature of the world easier to understand, define, quantify, visualize, or simulate. It requires selecting and identifying relevant aspects of a situation in the real world and then developing a model to replicate a system with those features. Different types of models may be used for different purposes, such as conceptual models to better understand, operational models to operationalize, mathematical models to quantify, computational models to simulate, and graphical models to visualize the subject.

Modelling is an essential and inseparable part of many scientific disciplines, each of which has its own ideas about specific types of modelling. The following was said by John von Neumann.

A hallucination is a perception in the absence of an external context stimulus that has the compelling sense of reality. They are distinguishable from several related phenomena, such as dreaming (REM sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional significance.

Hallucinations can occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. Hallucinations are referred to as multimodal if multiple sensory modalities occur.

In neuroanatomy, the optic tract (from Latin tractus opticus) is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus.

It is composed of two individual tracts, the left optic tract and the right optic tract, each of which conveys visual information exclusive to its respective contralateral half of the visual field. Each of these tracts is derived from a combination of temporal and nasal retinal fibers from each eye that corresponds to one half of the visual field. In more specific terms, the optic tract contains fibers from the ipsilateral temporal hemiretina and contralateral nasal hemiretina.

In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

The sense of balance or equilibrioception is the perception of balance and spatial orientation. It helps prevent humans and nonhuman animals from falling over when standing or moving. Equilibrioception is the result of a number of sensory systems working together; the eyes (visual system), the inner ears (vestibular system), and the body's sense of where it is in space (proprioception) ideally need to be intact.

The vestibular system, the region of the inner ear where three semicircular canals converge, works with the visual system to keep objects in focus when the head is moving. This is called the vestibulo-ocular reflex (VOR). The balance system works with the visual and skeletal systems (the muscles and joints and their sensors) to maintain orientation or balance. Visual signals sent to the brain about the body's position in relation to its surroundings are processed by the brain and compared to information from the vestibular and skeletal systems.