Inner eyeball has a visible-light receptor-cell layer {vision, anatomy}.
occipital lobe
Areas V2 and V4 detect contour orientation, regardless of luminance. Area V4 detects curved boundaries.
temporal lobe
Middle temporal-lobe area V5 detects pattern directions and motion gradients. Dorsal medial superior temporal lobe detects heading.
temporal lobe: inferotemporal lobe
Inferotemporal lobe (IT) detects shape parts. IT and CIP detect curvature and orientation.
retina and brain
Brain sends little feedback to retina [Brooke et al., 1965] [Spinelli et al., 1965].
pathways
Brain processes object recognition and color from area V1, to area V2, to area V4, to inferotemporal cortex. Cortical area V1, V2, and V3 damage impairs shape perception and pattern recognition, leaving only flux perception. Brain processes locations and actions in a separate faster pathway.
At first-ventricle top, chordates have cells {lamellar body} with cilia and photoreceptors. In vertebrates, lamellar body evolved to make parietal eye and pineal gland.
Cortical-neuron sets {spatial frequency channel} can detect different spatial-frequency ranges and so detect different object sizes.
Vision cells {vision, cells} are in retina, thalamus, and cortex.
One thousand cortical cells collectively {cardinal cell} code for one perception type.
Area-V4 neurons {color difference neuron} can detect adjacent and surrounding color differences, by relative intensities at different wavelengths.
Neurons {color-opponent cell} can detect output differences from different cone cells for same space direction.
Visual-cortex neurons {comparator neuron} can receive same output that eye-muscle motor neurons send to eye muscles, so perception can account for eye movements that change scenes.
Cells {double-opponent neuron} can have both ON-center and OFF-center circular fields and compare colors.
Some cortical cells {face cell} respond only to frontal faces, profile faces, familiar faces, facial expressions, or face's gaze direction. Face cells are in inferior-temporal cortex, amygdala, and other cortex. Face-cell visual field is whole fovea. Color, contrast, and size do not affect face cells [Perrett et al., 1992].
Some brain neurons {grandmother cell} {grandmother neuron} {Gnostic neuron} {place cell, vision} can recognize a perception or store a concept [Barlow, 1972] [Barlow, 1995] [Gross, 1998] [Gross, 2002] [Gross et al., 1969] [Gross et al., 1972] [Konorski, 1967]. Place cells recognize textures, objects, and contexts. For example, they fire only when animal sees face (face cell), hairbrush, or hand.
Small retinal cells {amacrine cell, vision} inhibit inner-plexiform-layer ganglion cells, using antitransmitter to block pathways. There are 27 amacrine cell types.
Photoreceptor cells excite retinal neurons {bipolar cell, vision}. There are ten bipolar-cell types. Parasol ganglion cells can receive from large-dendrite-tree bipolar cells {diffuse bipolar cell}.
input
Central-retina small bipolar cells {midget bipolar cell} receive from one cone. Peripheral-retina bipolar cells receive from more than one cone. Horizontal cells inhibit bipolar cells.
output
Bipolar cells send to inner plexiform layer to excite or inhibit ganglion cells, which can be up to five neurons away.
ON-center cells
ON-center midget bipolar cells increase output when light intensity increases in receptive-field center and/or decreases in receptive-field periphery. OFF-center midget bipolar cells increase output when light intensity decreases in receptive-field center and/or increases in receptive-field periphery.
Retinal neurons {ganglion cell, retina} can receive from bipolar cells and send to thalamus lateral geniculate nucleus (LGN), which sends to visual-cortex hypercolumns.
midget ganglion cell
Small central-retina ganglion cells {midget ganglion cell} receive from one midget bipolar cell. Midget cells respond mostly to contrast. Most ganglion cells are midget ganglion cells.
parasol cell
Ganglion cells {parasol cell} {parasol ganglion cell} can receive from diffuse bipolar cells. Parasol cells respond mostly to change. Parasol cells are 10% of ganglion cells.
X cell
Ganglion X cells can make tonic and sustained signals, with slow conduction, to detect details and spatial orientation. X cells send to thalamus simple cells. X cells have large dendritic fields. X cells are more numerous in fovea.
Y cell
Ganglion Y cells can make phasic and transient signals, with fast conduction, to detect stimulus size and temporal motion. Y cells send to thalamus complex cells. Y cells have small dendritic fields. Y cells are more numerous in retinal periphery.
W cell
Ganglion W cells are small, are direction sensitive, and have slow conduction speed.
ON-center neuron
ON-center ganglion cells respond when light intensity above background level falls on their receptive field. Light falling on field surround inhibits cell. Bipolar cells excite ON-center neurons.
Four types of ON-center neuron depend on balance between cell excitation and inhibition. One has high firing rate at onset and zero rate at offset. One has high rate at onset, then zero, then high, and then zero. One has high rate at onset, goes to zero, and then rises to constant level. One has high rate at onset and then goes to zero.
OFF-center neuron
OFF-center ganglion cells increase output when light intensity decreases in receptive-field center. Light falling on field surround excites cell. Bipolar cells excite OFF-center neurons.
ON-OFF-center neuron
ON-OFF-center ganglion cells for motion use ON-center-neuron time derivatives to find movement position and direction. Amacrine cells excite transient ON-OFF-center neurons.
similar neurons
Ganglion cells are like auditory nerve cells, Purkinje cells, olfactory bulb cells, olfactory cortex cells, and hippocampal cells.
spontaneous activity
Ganglion-cell spontaneous activity can be high or low [Dowling, 1987] [Enroth-Cugell and Robson, 1984] [Wandell, 1995].
Retinal cells {horizontal cell} can receive from receptor cells and inhibit bipolar cells.
Retina has pigment cells {photoreceptor cell}, with three layers: cell nucleus, then inner segment, and then outer segment with photopigment. Visual-receptor cells find illumination logarithm.
types
Human vision uses four receptor types: rods, long-wavelength cones, middle-wavelength cones, and short-wavelength cones.
hyperpolarization
Visual receptor cells hyperpolarize up to 30 mV from resting level [Dowling, 1987] [Enroth-Cugell and Robson, 1984] [Wandell, 1995]. Photoreceptors have maximum response at one frequency and lesser responses farther from that frequency.
Rod-shaped retinal cells {rod cell} are night-vision photoreceptors, detect large features, and do not signal color.
frequency
Rods have maximum sensitivity at 498 nm, blue-green.
Just above cone threshold intensity {mesopic vision, rod}, rods are more sensitive to short wavelengths, so blue colors are brighter but colorless.
number
Retinas have 90 million rod cells.
layers
Rods have cell nucleus layer, inner layer that makes pigment, and outer layer that stores pigment. Outer layer is next to pigment epithelium at eyeball back.
size
Rods are larger than cones.
pigment
Rod light-absorbing pigment is rhodopsin. Cones have iodopsin.
rod cell and long-wavelength cone
Brain can distinguish colors using light that only affects rod cells and long-wavelength cone cells.
fovea
Fovea has no rod cells. Rod cells are denser around fovea.
Cone-shaped retinal cells {cone, cell} have daylight-vision photoreceptors and detect color and visual details.
types
Humans have three cone types. Cone maximum wavelength sensitivities are at indigo 437 nm {short-wavelength cone}, green 534 nm {middle-wavelength cone}, and yellow-green 564 nm {long-wavelength cone}. Shrimp can have eleven cone types.
evolution
Long-wavelength cones evolved first, then short-wavelength cones, and then middle-wavelength cones. Long-wavelength and short-wavelength cones differentiated 30,000,000 years ago. Three cone types and trichromatic vision began in Old World monkeys.
fovea
Fovea has patches of only medium-wavelength or only long-wavelength cones. To improve acuity, fovea has few short-wavelength cones, because different colors focus at different distances. Fovea center has no short-wavelength cones [Curcio et al., 1991] [Roorda and Williams, 1999] [Williams et al., 1981] [Williams et al., 1991].
number
There are five million cones, mostly in fovea. Short-wavelength cones are mostly outside fovea.
size
Cones are smaller than rods.
pigment
Cone light-absorbing pigment is iodopsin. Rods have rhodopsin.
frequency
When rods saturate, cones have approximately same sensitivity to blue and red.
Just above cone threshold {mesopic vision, cone}, rods are more sensitive to short wavelengths, so blue colors are brighter but colorless. Retinal receptors do not detect pure or unmixed colors. Red light does not optimally excite one cone type but makes maximum excitation ratio between two cone types. Blue light excites short-wavelength cones and does not excite other cone types. Green light excites all cone types.
output
Cones send to one ON-center and one OFF-center midget ganglion cell.
Most mammals, including cats and dogs, have two photopigments and two cone types {dichromat}. For dogs, one photopigment has maximum sensitivity at 429 nm, and one photopigment has maximum sensitivity at 555 nm. Early mammals and most mammals are at 424 nm and 560 nm.
Animals can have only one photopigment and one cone type {monochromat} {cone monochromat}. They have limited color range. Animals can have only rods and no cones {rod monochromat} and cannot see color.
Reptiles and birds have four different photopigments {quadchromat}, with maximum sensitivities at near-ultraviolet 370 nm, 445 nm, 500 nm, and 565 nm. Reptiles and birds have yellow, red, and colorless oil droplets, which make wavelength range less, except for ultraviolet sensor.
Women can have two different long-wavelength cones {L-cone} {L photopigment}, one short-wavelength cone {S-cone} {S photopigment}, and one middle-wavelength cone {M-cone} {M photopigment}, and so have four different pigments {tetrachromacy}. Half of men have one or the other long-wavelength cone [Asenjo et al., 1994] [Jameson et al., 2001] [Jordan and Mollon, 1993] [Nathans, 1999].
People with normal color vision have three different photopigments and cones {trichromat}.
Land-vertebrate eyes {eye} are spherical and focus images on retina.
eye muscles
Eye muscles exert constant tension against movement, so effort required to move eyes or hold them in position is directly proportional to eye position. Midbrain oculomotor nucleus sends, in oculomotor nerve, to inferior oblique muscle below eyeball, superior rectus muscle above eyeball, inferior rectus muscle below eyeball, and medial rectus muscle on inside. Pons abducens nucleus sends, in abducens nerve, to lateral rectus muscle on outside. Caudal midbrain trochlear nucleus sends, in trochlear nerve, to superior oblique muscle around light path from above eyeball.
eye muscles: convergence
Eyes converge toward each other as object gets nearer than 10 meters.
eye muscles: zero-gravity
In zero-gravity environment, eye resting position shifts upward, but people are not aware of shift.
fiber projection
Removing embryonic eye and re-implanting it in rotated positions does not change nerve fiber projections from retina onto visual cortex.
Horseshoe crab (Limulus) eye {simple eye} can only detect light intensity, not direction. Input/output equation uses relation between Green function and covariance, because synaptic transmission is probabilistic.
Most mammals and birds have tissue fold {inner eyelid} {palpebra tertia} that, when eye retracts, comes down from above eye to cover cornea. Inner eyelid has outside mucous membrane {conjunctiva}, inner-side lymphoid follicles, and lacrimal gland.
Reptiles and other vertebrates have transparent membrane {nictitating membrane}| that can cover and uncover eye.
Eye has transparent cells {cornea}| protruding in front. Cornea provides two-thirds of light refraction. Cornea has no blood vessels and absorbs nutrients from aqueous humor. Cornea has many nerves. Non-spherical-cornea astigmatism distorts vision. Corneas can transplant without rejection.
Elastic and transparent cell layers {lens, eye} {crystalline lens} attach to ciliary muscles that change lens shape. To become transparent, lens cells destroy all cell organelles, leaving only protein {crystallin} and outer membrane. Lens cells are all the same. They align and interlock [Weale, 1978]. Lens shape accommodates when objects are less than four feet away. Lens maximum magnification is 15.
Sphincter muscles in a colored ring {iris, eye}| close pupils. When iris is translucent, light scattering causes blue color. In mammals, autonomic nervous system controls pupil smooth muscles. In birds, striate muscles control pupil opening.
Eye has opening {pupil}| into eye. In bright light, pupil is 2 mm diameter. At twilight, pupil is 10 mm diameter. Iris sphincter muscles open and close pupils. Pupil reflex goes from one eye to the other.
Eyeball has insides {fundus, eye}.
Liquid {aqueous humor}| can be in anterior chamber behind cornea and nourish cornea and lens.
Liquid {vitreous humor}| fills main eyeball chamber between lens and retina.
Eyeball has outer white opaque connective-tissue layer {sclera}|.
Eye regions {trochlea}| can have eye muscles.
Eyeball has inner blood-vessel layer {choroid}.
Between retina and choroid is a cell layer {retinal pigment epithelium} (RPE) and Bruch's membrane. RPE cells maintain rods and cones by absorbing used molecules.
Retinal-pigment epithelium and membrane {Bruch's membrane} {Bruch membrane} are between retina and choroid.
At back inner eyeball, visual receptor-cell layers {retina}| have 90 million rod cells, one million cones, and one million optic nerve axons.
cell types
Retina has 50 cell types.
cell types: clustering
Retina has clusters of same cone type. Retina areas can lack cone types. Fovea has few short-wavelength cones.
development
Retina grows by adding cell rings to periphery. Oldest eye part is at center, near where optic nerve fibers leave retina. In early development, contralateral optic nerve fibers cross over to connect to optic tectum. In early development, optic nerve fibers and brain regions have topographic maps. After maturation, axons can no longer alter connections.
processing
Retina cells separate information about shape, reflectance, illumination, and viewpoint.
Ganglion-cell axons leave retina at region {blindspot}| medial to fovea [DeWeerd et al., 1995] [Finger, 1994] [Fiorani, 1992] [Komatsu and Murakami, 1994] [Komatsu et al., 2000] [Murakami et al., 1997].
Cone cells are Long-wavelength, Middle-wavelength, or Short-wavelength. Outside fovea, cones can form two-dimensional arrays {color-receptor array} with L M S cones in equilateral triangles. Receptor rows have ...S-M-L-S-M-L-S... Receptor rows above, and receptor rows below, are offset a half step: ...-L-S-M-L-S-M-.../...S-M-L-S-M-L-S.../...-L-S-M-L-S-M-...
hexagons
Cones have six different cones around them in hexagons: three of one cone and three of other cone. No matter what order the three cones have, ...S-M-L-S-M..., ...S-L-M-S-L..., or ...M-L-S-M-L..., M and L are beside each other and S always faces L-M pair, allowing red+green brightness, red-green opponency, and yellow-blue opponency. L receptors work with three surrounding M receptors and three surrounding S receptors. M receptors work with three surrounding L receptors and three surrounding S receptors. S receptors work with six surrounding L+M receptor pairs, which are from three equilateral triangles, so each S has three surrounding L and three surrounding M receptors.
In all directions, fovea has alternating long-wavelength and middle-wavelength cones: ...-L-M-L-M-.
Primates have central retinal region {fovea}| that tracks motions and detects self-motion. Retinal periphery detects spatial orientation. Fovea contains 10,000 neurons in a two-degree circle. Fovea has no rods. Fovea center has no short-wavelength cones. Fovea has patches of only medium-wavelength cones or only long-wavelength cones. Fovea has no blood vessels, which pass around fovea.
Retinal layers {inner plexiform layer} can have bipolar-cell and amacrine-cell axons and ganglion-cell dendrites. There are ten inner plexiform layers.
Near retina center is a yellow-pigmented region {macula lutea}| {yellow spot}. Yellow pigment increases with age. If incident light changes spectra, people can briefly see macula image {Maxwell spot}.
Lateral-geniculate-nucleus magnocellular neurons measure luminance {luminance channel, vision} {achromatic channel} {spectrally non-opponent channel}.
Lateral-geniculate-nucleus parvocellular neurons measure colors {chromatic channel} {spectrally opponent channel}.
Regions {horizontal gaze center}, near pons abducens nucleus, can detect right-to-left and left-to-right motions.
Regions {vertical gaze center}, near midbrain oculomotor nucleus, can detect up and down motions.
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Date Modified: 2022.0225