Chapter 7 (Vision: From Eye to Brain) Flashcards
retina
The receptive surface inside the eye that contains photoreceptors and other neurons.
transduction
The conversion of one form of energy to another, as converting light into neuronal activity.
cornea
The transparent outer layer of the eye, whose curvature is fixed. The cornea bends light rays and is primarily responsible for forming the 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.
lens
A structure in the eye that helps focus an image of the retina.
ciliary muscle
One of the muscles that control the shape of the lens inside the eye, focusing an image on the retina.
accommodation
The process by which the ciliary muscles adjust the lens to focus a sharp image on the retina.
myopia
Nearsightedness; the inability to focus the retinal image of objects that are far away.
extracellular muscle
One of the muscles attached to the eyeball that control its position and movements.
photoreceptor
A neural cell in the retina that responds to light.
rod
A photoreceptor cell in the retina that is most active at low levels of light.
cone
Any of several classes of photoreceptor cells in the retina that are responsible for color vision.
bipolar cell
An interneuron in the retina that receives information from rods and cones and passes the information to retinal ganglion cells.
ganglion cell
Any of a class 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 brain.
horizontal cell
A specialized retinal cell that contacts both receptor cells and bipolar cells.
amacrine cell
A specialized retinal cell that contacts both bipolar cells and ganglion cells, and is especially significant in inhibitory interactions within the retina.
scotopic system
A system in the retina that operates low levels of light and involves the rods.
convergence
The phenomenon of neural connections in which many cells send signals to a single cell.
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.
pupil
The opening 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.
range fractionation
The means by which sensory systems cover a wide range of intensity values, as each sensory receptor cell specializes in just one part of the overall range of intensities.
photoreceptor adaptation
The tendency of rods and cones to adjust their light sensitivity to match ambient levels of illumination.
visual acuity
Sharpness of vision.
fovea
The central portion of the retina, which is packed by the highest density of photoreceptors and is the center of our gaze.
optic disc
The region of the retina that is 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 the light falls on the optic disc. Because there are no receptors in this region, light striking the blind spot cannot be seen.
occipital cortex
Also called visual cortex. The cortex of the occipital lobe of the brain.
optic chiasm
The point at which the two optic nerves meet.
optic tract
The axons of retinal ganglion cells after they have passed the optic chiasm; most of these axons terminate in the lateral geniculate nucleus.
lateral geniculate nucleus (LGN)
The part of the thalamus that receives information from the optic tract and sends it to visual areas in the occipital cortex.
optic radiation
Axons from the LGN 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.
binocular
Two-eyed.
extrastriate cortex
Visual cortex outside of the primary visual (striate) cortex.
visual field
The whole area that you can see without moving your head or eyes.
topographic projection
A mapping that preserves the pont-to-point correspondence between neighboring parts space. For example, the retina extends a topographic projection onto the cortex.
scotoma
A region of blindness within the visual fields, caused by injury to the visual pathway or brain.
blindsight
The paradoxical phenomenon whereby, within a scotoma, a person cannot consciously perceive visual cues but still may be able to make some visual discrimination.
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 the cell’s receptive field.
on-center/off-surround
Referring to a concentric receptive field in which stimulation of the center excites the cell of interest while stimulation of the surround inhibits it.
off-center/on-surround
Referring to a concentric receptive field in which stimulation of the center inhibits the cell of interest while stimulation of the surround excites it.
lateral inhibition
The phenomenon by which interconnected neurons inhibit their neighbors, producing contrast at the edges of regions.
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 that responds best to a bar of a particular size and orientation anywhere within a particular area of the visual field.
spatial-frequency model
A model of vision that emphasizes the analysis of different spatial frequencies, of various orientations and in various parts of the visual field, as the basis of visual perception of form.
wavelength
The length between two peaks in a repeated stimulus such as a wave, light, or sound.
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
A hypothesis of color perception stating that different systems 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.
optic ataxia
Spatial disorientation in which the patient is unable to accurately reach for objects using visual guidance.
amblyopia
Reduced visual acuity that is not caused by optical or retinal impairments.
