Vision

brightness

1. The state or quality of being bright. 2. The effect or sensation by means of which an observer is able to distinguish differences in luminance. 3. The dimension of a color that represents its similarity to one of a series of achromatic colors ranging from very dim (dark) to very bright (dazzling).

ommatidia

An ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells. The outer part of the ommatidium is overlaid with a transparent cornea.

cones

Cones, which are abundant in and near the fovea, are less active in dim light, more useful in bright light, and essential for color vision. Because of the distribution of rods and cones, you have good color vision in the fovea but not in the periphery.

light waves

Electromagnetic waves, including visible light, are made up of oscillating electric and magnetic fields as shown. The wavelength of a wave is the distance between successive peaks or troughs of a wave.

hyperopia

Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects can be seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature. In these cases, your eye can't correctly focus the light that enters it.

saturation

In color theory, saturation or purity refers to the intensity of a specific hue.

choroid

In the eye, a thin vascular layer between the sclera and the retina. The choroid supplies blood to the retina and conducts arteries and nerves to other structures in the eye.

retina

It is focused by the lens (ad- justable) and cornea (not adjustable) and projected onto the retina, the rear surface of the eye, which is lined with visual re- ceptors

dark adaption

LIGHT AND DARK ADAPTATION. Rhodopsin is an extremely sensitive molecule. As long as the light is of low intensity, rods quickly regenerate rhodopsin and the retina continues to respond to light stimuli.

pupil

Light enters the eye through an opening in the center of the iris called the pupil

lateral geniculate nucleus

Most ganglion cell axons go to the lateral geniculate nucleus, part of the thalamus. ( e term geniculate comes from the Latin root genu, meaning "knee." To genu ect is to bend the knee. Thee lateral geniculate looks a little like a knee, if you use some imagination.) A smaller number of axons go to the superior colliculus and other areas, including part of the hypothalamus that controls the waking-sleeping lateral geniculate, in turn, sends axons to other parts of the thalamus and the occipital cortex. e cortex returns many axons to the thalamus, so the thalamus and cortex constantly feed information back and forth

myopia

Nearsightedness, or myopia, is the most common refractive error of the eye, and it has become more prevalent in recent years.

neural process

Neural processing originally referred to the way the brain works, but the term is more typically used to describe a computer architecture that mimics that biological function. In computers, neural processing gives software the ability to adapt to changing situations and to improve its function as more information becomes available. Neural processing is used in software to do tasks such as recognize a human face, predict the weather, analyze speech patterns, and learn new strategies in games.

photopic

Photopic vision is the vision of the eye under well-lit conditions (luminance level 10 to 108 cd/m²). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visual acuity and temporal resolution than available with scotopic vision.

scotopic

Scotopic vision is the vision of the eye under low light conditions. The term comes from Greek skotos meaning darkness and -opia meaning a condition of sight.[1] In the human eye cone cells are nonfunctional in low light - scotopic vision is produced exclusively through rod cells which are most sensitive to wavelengths of light around 498 nm (green-blue) and are insensitive to wavelengths longer than about 640 nm (red). Scotopic vision is dominated by retina amacrine cells, specifically all-amacrine cells. AII-amacrine cells capture rod bipolar cell input and redistribute it to cone bipolar cells since rod-driven bipolar cells do not synapse on ganglion cells

superior colliculus

Since the latter category includes visual, auditory and somatosensory inputs, you can see that the superior colliculus is not exclusively related to visual function. Instead, it plays a role in helping orient the head and eyes to all types of sensory stimuli.

W cells (koniocellular neurons)

The Koniocellular neurons have small cell bodies, similar to the parvocel- lular neurons, but they occur throughout the retina. (Koniocel- lular means "dust celled," from the Greek root meaning "dust." ey got this name because of their granular appearance.)

purkinje effect

The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation and named after the Czech anatomist Jan Evangelista Purkyně) is the tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels. This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, or adjacent blue flowers, but in the same scene viewed at dusk, the contrast is reversed, with the red petals appearing a dark red or black, and the leaves and blue petals appearing relatively bright.

aqueous humor

The aqueous humour is a transparent, watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens.

perstriate (parastriate) cortex

The area outside the visual cortex (V1).

corena

The cornea is the transparent part of the eye that covers the front portion of the eye. It covers the pupil (the opening at the center of the eye), iris (the colored part of the eye), and anterior chamber (the fluid-filled inside of the eye). The cornea's main function is to refract, or bend, light. The cornea is responsible for focusing most of the light that enters the eye. The cornea is composed of proteins and cells. It does not contain blood vessels, unlike most of the tissues in the human body. Blood vessels may cloud the cornea, which may prevent it from refracting light properly and may adversely affect vision.

horizontal cells

The horizontal cells make inhibitory contact onto bipolar cells, which in turn make synapses onto amacrine cells and ganglion cells. All these cells are within the eyeball.

lens

The lens is located in the eye. By changing its shape, the lens changes the focal distance of the eye. In other words, it focuses the light rays that pass through it (and onto the retina) in order to create clear images of objects that are positioned at various distances.

optic disk (blind spot)

The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small physiological blind spot in each eye.

rods

The rods, which are abundant in the periphery of the human retina, respond to faint light but are not useful in daylight because bright light bleaches them.

wavelength

The visible colors from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light. Infrared radiation has a longer wavelength than visible red light. The white light is a mixture of the colors of the visible spectrum.

vitreous humor

The vitreous body is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous humour or simply "the vitreous".

transduction

Visual phototransduction is the sensory transduction of the visual system. It is a process by which light is converted into electrical signals in the rod cells, cone cells and photosensitive ganglion cells of the retina of the eye.

opponent-process theory

We perceive color in terms of opposites at is, the brain has a mechanism that perceives color on a continuum from red to green, another from yellow to blue, and another from white to black. opponent process cells respond to short wavelengths but are inhibited from firing by long wavelengths or vice verse. (reddish orange or greenish blue) NOT Reddish green

sclera

a dense, white, fibrous membrane that, with the cornea, forms the external covering of the eyeball.

iris

a flat, colored, ring-shaped membrane behind the cornea of the eye, with an adjustable circular opening (pupil) in the center.

iodopsin

a photosensitive violet pigment in the retinal cones that is similar to rhodopsin but more labile, is formed from vitamin A, and is important in daylight vision

fovea centralis

a small depression in the retina of the eye where visual acuity is highest. The center of the field of vision is focused in this region, where retinal cones are particularly concentrated.

functional coding

additional code that helps us discern between differences in firing codes in the brain (Red vs. Pink, Pinprick vs. Kiss etc.)

amacrine cells

amacrine cells get information from bipolar cells and send it to other bipolar, amacrine, and ganglion cells. Various types of amacrine cells refine the input to ganglion cells, enabling them to respond specically to shapes, movements, or other visual features

infratemporal (inferior temporal) cortex

being the inferior part of the temporal lobe of the cerebral cortex; also : situated or occurring in, on, or under this part

complex cells

can be found in the primary visual cortex (V1),[1] the secondary visual cortex (V2), and Brodmann area 19 (V3).[2] Like a simple cell, a complex cell will respond primarily to oriented edges and gratings, however it has a degree of spatial invariance. This means that its receptive field cannot be mapped into fixed excitatory and inhibitory zones. Rather, it will respond to patterns of light in a certain orientation within a large receptive field, regardless of the exact location. Some complex cells respond optimally only to movement in a certain direction. These cells were discovered by Torsten Wiesel and David Hubel in the early 1960s.[1] They refrained from reporting on the complex cells in (Hubel 1959) because they did not feel that they understood them well enough at the time.[3] In Hubel and Wiesel (1962),[1] they reported that complex cells were intermixed with simple cells and when excitatory and inhibitory regions could be established, the summation and mutual antagonism properties didn't hold.

Anatomical coding

different sensations are coded by which incoming nerve fibres are active

hue

dimension of visual experience specified by color names. Short waves are violet/blue, longer waves are red/orange.

ganglion cells

ganglion cells, located still closer to the center of the eye. e ganglion cells' axons join to- gether and travel back to the brain

doctrine of specific energries

in 1838, Johannes Müller described this insight as the law of specific nerve energies. Müller held that whatever excites a particular nerve establishes a special kind of energy unique to that nerve. In modern terms, the brain somehow interprets the action potentials from the auditory nerve as sounds, those from the olfactory nerve as odors, and so forth. Admittedly, that word "somehow" glosses over a deep mystery.

adaption

in response to varying ambient light levels, rods and cones of eye function both in isolation and in tandem to adjust the visual system. Changes in the sensitivity of rods and cones in the eye are the major contributors to dark adaptation.

simple cells

in the primary visual cortex is a cell that responds primarily to oriented edges and gratings (bars of particular orientations). These cells were discovered by Torsten Wiesel and David Hubel in the late 1950s.[1] Hubel and Wiesel named these cells "simple," as opposed to "complex cell", because they shared the following properties:[2] They have distinct excitatory and inhibitory regions. These regions follow the summation property. These regions have mutual antagonism - excitatory and inhibitory regions balance themselves out in diffuse lighting. It is possible to predict responses of moving stimuli given the map of excitatory and inhibitory regions.

bipolar cells

in the vertebrate retina, however, messages go from receptors at the back of the eye to bipolar cells, located closer to the center of the eye. e bipolar cells send their messages to ganglion cells

hyper complex (end stopped) cells

is a type of visual processing neuron in the mammalian cerebral cortex. Initially discovered by David Hubel and Torsten Wiesel in 1965, hypercomplex cells are defined by the property of end-stopping, which is a decrease in firing strength with increasingly larger stimuli. The sensitivity to stimulus length is accompanied by selectivity for the specific orientation, motion, and direction of stimuli. For example, a hypercomplex cell may only respond to a line at 45˚ that travels upward. Elongating the line would result in a proportionately weaker response. Ultimately, hypercomplex cells can provide a means for the brain to visually perceive corners and curves in the environment by identifying the ends of a given stimulus

mach bands

is an optical illusion named after the physicist Ernst Mach. It exaggerates the contrast between edges of the slightly differing shades of gray, as soon as they contact one another, by triggering edge-detection in the human visual system. The Mach bands effect is due to the spatial high-boost filtering performed by the human visual system on the luminance channel of the image captured by the retina. This filtering is largely performed in the retina itself, by lateral inhibition among its neurons

lateral inhibition

lateral inhibition, the reduction of activity in one neuron by activity in neighboring neurons . Lateral inhibition heightens contrast. When light falls on a surface, as shown here, the bipolars just inside the border are most excited, and those outside the border re- spond the least.

X cells (parvocellular neurons)

parvocellular neurons, with small cell bodies and small receptive fields, are mostly in or near the fovea. (Parvocellular means "small celled," from the Latin root parv, meaning "small.")

rhodopsin

photopigment of rods - pink --> bleached when split by light - rods not sensitive to bright light because: rate of bleaching > rate of recovery - dark adaptation: rate of recovery > rate of bleaching

striate cortex

primary visual cortex in the occipital cortex, also known as area V1 or the striate cortex because of its striped appearance. the region of the cerebral cortex occupying the entire surface of the occipital lobe, and composed of Brodmann areas 17-19. Brodmann area 17 (which is also called striate cortex or area because the line of Gennari is grossly visible on its surface) is the primary visual cortex, receiving the visual radiation from the lateral geniculate body of the thalamus. The surrounding Brodmann areas 18 (parastriate cortex or area) and 19 (peristriate cortex or area) are probably involved in subsequent steps of visual information processing; Brodmann area 18 is referred to as the secondary visual cortex.

visual receptive field

receptive field of an individual sensory neuron is the particular region of the sensory space (e.g., the body surface, or the visual field) in which a stimulus will trigger the firing of that neuron. This region can be a hair in the cochlea or a piece of skin, retina, tongue or other part of an animal's body.

Generator potential

stationary depolarization of a receptor that occurs in response to a stimulus and is graded according to its intensity and that results in an action potential when the appropriate threshold is reached

optic nerves

the ganglion cell axons form the optic nerve, which exits through the back of the eye. e point at which it leaves (which is also where the blood vessels enter and leave) is the blind spot because it has no receptors.

Y cells (magnocellular neurons)

the magnocellular neurons, with larger cell bodies and receptive fields, are distributed evenly throughout the retina. (Magnocellular means"large celled,"from the Latin root magn, meaning"large." thee same root appears in magnify.)

ciliary muscles

the part of the eye that connects the iris to the choroid. It consists of the ciliary muscle (which alters the curvature of the lens), a series of radial ciliary processes (from which the lens is suspended by ligaments), and the ciliary ring (which adjoins the choroid).

cyanolabe

the pigment in retinal cones that is more sensitive to the blue range of the spectrum than are chlorolabe and erythrolabe.

chlorolabe

the pigment in retinal cones that is more sensitive to the green portion of the spectrum than are the other pigments (cyanolabe and erythrolabe).

erythrolabe

the pigment in retinal cones that is more sensitive to the red range of the spectrum than are the other pigments (chlorolabe and cyanolabe).

amplitude

the size of a stimulant or reaction. 2. the highest worth of a sinusoid wave.

trichromatic theory

trichromatic theory of color vision, also known as the Young-Helmholtz theory of color vision, there are three receptors in the retina that are responsible for the perception of color. One receptor is sensitive to the color green, another to the color blue and a third to the color red. These three colors can then be combined to form any visible color in the spectrum.