10 - Vision: From Eye to Brain Flashcards
Visual acuity
Sharpness of vision
Vision field
The whole area that you can see without moving your head or eyes
Photoreceptors
Neural cells in the retina that respond to light
Lateral inhibition
The phenomenon by which interconnected neurons inhibit their neighbors, producing contrast at the edges of regions
Quantum (pl. quanta)
A unit of radiant energy
Wavelength
The length between two peaks in a repeated stimulus such as a wave, light, or sound
Photon
A quantum of light energy
Cornea
The transparent outer layer of the eye, whose curvature is fixed. It bends light rays and is primarily responsible for forming the image on the retina
Lens
A structure in the eye that helps focus an image on the retina
Refraction
The bending of light rays by a change in the density of a medium, such as the cornea and the lens of the eyes
Ciliary muscle
One of the muscles that controls the shape of the lens inside the eye, focusing an image on the retina
Accommodation
The process of focusing by the ciliary muscles and the lens to form a sharp image on the retina
Pupil
The aperture, formed by the iris, that allows light to enter the eye
Iris
The circular structure of the eye that provides an opening to form the pupil
Extraocular muscle
One of the muscles attached to the eyeball that control its position and movements
Retina
The receptive surface inside the eye that contains photoreceptors and other neurons
Rods
A class of light-sensitive receptor cells (photoreceptors) in the retina that are most active at low levels of light
Cones
A class of photoreceptor cells in the retina that are responsible for color vision
Bipolar cells
A class of interneurons of the retina that receive information from rods and cones and pass the information to retinal ganglion cells
Ganglion cells
A glass of cells in the retina whose axons form the optic nerve
Optic nerve
Cranial nerve II; The collection of ganglion cell axons that extend from the retina to the optic chiasm
Horizontal cells
Specialized retinal cells that contact both the receptor cells and the bipolar cells
Amacrine cells
Specialized retinal cells that contact both the bipolar cells and the ganglion cells, and are especially significant in inhibitory interactions within the retina
Scotopic system
A system in the retina that operates at low levels of light and involves the rods
Photopic system
A system in the retina that operates at high levels of light, shows sensitivity to color, and involves the cones
Rhodopsin
The photopigment in rods that responds to light
Retinal
One of the two components of photopigments in the retina
Opsin
One of the two components of photopigments in the retina
Range fractionation
A hypothesis of stimulus intensity perception stating that a wide range of intensity values can be encoded by a group of cells, each of which is a specialist for particular range of stimulus intensities
Photoreceptor adaptation
The tendency of rods and cones to adjust their light sensitivity to match ambient levels of illumination
Fovea
The central portion of the retina, packed with the most photoreceptors and therefore the center of our gaze
Optic disc
The region of the retina devoid of receptor cells because ganglion cell axons and blood vessels exit the eyeball there
Blind spot
The portion of the visual field from which light falls on the optic disc. Because there are no receptors in this region, light striking it cannot be seen
Optic chiasm
The point at which the two optic nerves meet
Optic tract
The axon of retinal ganglion cells after they have passed the optic chiasm; most terminate in the lateral geniculate nucleus
Lateral geniculate nucleus (LGN)
The part of the thalamus that receives information from the optic track and sends it to visual areas in the occipital cortex
Optic radiation
Axons from the lateral geniculate nucleus that terminate in the primary visual areas of the occipital cortex
Primary visual cortex (V1) or striate cortex
Also called area 17. The region of the occipital cortex where most visual information first arrives
Occipital cortex
Also called visual cortex. The cortex of the occipital lobe of the brain
Extrastriate cortex
Visual cortex outside of the primary visual (striate) cortex
Scotoma
A region of blindness caused by injury to the visual pathway or brain
Receptive field
The stimulus region and features that affect the activity of a cell in a sensory system
On-center bipolar cell
A retinal bipolar cell that is excited by light in the center of its receptive field
Off-center bipolar cell
A retinal bipolar cell that is inhibited by light in the center of its receptive field
On-center ganglion cell
A retinal ganglion cell that is activated when light is presented to the center, rather than the periphery, of the cell’s receptive field
Off-center ganglion cell
A retinal ganglion cell that is activated when light is presented to the periphery, rather than the center, of a cell’s receptive field
On-center/off-surround
Referring to a concentric receptive field in which the center excites this cell of interest while the surround inhibits it
Off-center/on-surround
Referring to a concentric receptive field in which the center inhibits the cell of interest while the surround excites it
Parvocellular
Of or consisting of relatively small cells
Magnocellular
Of or consisting of relatively large cells
Simple cortical cell
Also called bar detector or edge detector. A cell in the visual cortex that responds best to an edge or a bar that has a particular width, as well as a particular orientation and location in the visual field
Complex cortical cell
A cell in the visual cortex the responds best to a bar of particular size and orientation anywhere within a particular area of the visual field
Spatial-frequency filter model
A model of pattern analysis that emphasizes Fourier analysis of visual stimuli
Ocular dominance column
A region of cortex in which one eye or the other provides a greater degree of synaptic input
Ocular dominance slab
A slab of visual cortex, about .5 mm wide, in which the neurons of all layers respond preferentially to stimulation of one eye
Orientation column
A column of visual cortex that responds to rod-shaped stimuli of a particular orientation
Brightness
One of three basic dimensions of light perception, varying from dark to light
Hue
One of three basic dimensions of light perception, varying around the color circle through blue, green, yellow, orange, and red
Saturation
One of three basic dimensions of light perception, varying from rich to pale
Trichromatic hypothesis
A hypothesis of color perception stating that there are three different types of cones, each excited by a different region of the spectrum and each having a separate pathway to the brain
Opponent-process hypothesis
The theory that color vision depends on systems that produce opposite responses to light of different wavelengths
Spectrally opponent cell
A visual receptor cell that has opposite firing responses to different regions of the spectrum
Ataxia
An impairment in the direction, extent, and rate of muscular movement
Mirror neuron
A neuron that is active both when an individual makes a particular movement and when that individual sees another individual make that same movement
Myopia
Nearsightedness; The inability to focus the retinal image of objects that are far away
Amblyopia
Reduced visual acuity that is not caused by optical or retinal impairments
