Chapter 10 Flashcards

accommodation
The process of focusing by the ciliary muscles and the lens to form a sharp image on the retina.
adaptation
1. In the context of evolution, a trait that increases the probability that an individual will leave offspring in subsequent generations. 2. In the context of sensory processing, the progressive loss of receptor sensitivity as stimulation is maintained. See Figure 8.7.
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.
amblyopia
Reduced visual acuity that is not caused by optical or retinal impairments.
bipolar cells
A class of interneurons of the retina that receive information from rods and cones and pass the information to retinal ganglion cells. See Figure 10.2. See also amacrine cells.
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.
brightness
One of three basic dimensions (along with hue and saturation) of light perception. Brightness varies from dark to light. See Figure 10.23.
ciliary muscle
One of the muscles that controls the shape of the lens inside the eye, focusing an image on the retina. See Figure 10.1.
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. Compare simple cortical cell.
cones
A class of photoreceptor cells in the retina that are responsible for color vision. See Figure 10.2. Compare rods.
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. See Figure 10.1.
extraocular muscle
One of the muscles attached to the eyeball that control its position and movements.
extrastriate cortex
Visual cortex outside of the primary visual (striate) cortex.
fovea
The central portion of the retina, packed with the most photoreceptors and therefore the center of our gaze. See Figure 10.5.
ganglion cells
A class of cells in the retina whose axons form the optic nerve. See Figure 10.8. See also amacrine cells and bipolar cells.
horizontal cells
Specialized retinal cells that contact both the receptor cells and the bipolar cells.
hue
One of three basic dimensions (along with brightness and saturation) of light perception. Hue varies around the color circle through blue, green, yellow, orange, and red. See Figure 10.23.
iris
The circular structure of the eye that provides an opening to form the pupil. See Figure 10.1.
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. See Figure 10.14.
lateral inhibition
The phenomenon by which interconnected neurons inhibit their neighbors, producing contrast at the edges of regions. See Figure 10.8.
lens
A structure in the eye that helps focus an image on the retina. The shape of the lens is controlled by the ciliary muscles inside the eye. See Figure 10.1.
magnocellular
Of or consisting of relatively large cells. Compare parvocellular.
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.
occipital lobes
Large regions of cortex covering much of the posterior part of each cerebral hemisphere, and specialized for visual processing. See Figure 2.12.
ocular dominance column
A region of cortex in which one eye or the other provides a greater degree of synaptic input. See Figure 10.22.
ocular dominance slab
A slab of visual cortex, about 0.5 mm wide, in which the neurons of all layers respond preferentially to stimulation of one eye. See Figure 10.23.
off-center bipolar cell
A retinal bipolar cell that is inhibited by light in the center of its receptive field. See Figure 10.13. Compare on-center bipolar cell.
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. See Figure 10.12. Compare on-center ganglion cell.
off-center/on-surround
Referring to a concentric receptive field in which the center inhibits the cell of interest while the surround excites it. See Figure 10.13. Compare on-center/off-surround.
on-center bipolar cell
A retinal bipolar cell that is excited by light in the center of its receptive field. See Figure 10.13. Compare off-center bipolar cell.
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. See Figure 10.12. Compare off-centerganglion cell.
on-center/off-surround
Referring to a concentric receptive field in which the center excites the cell of interest while the surround inhibits it. See Figure 10.13. Compare off-center/on-surround.
opponent-process hypothesis
The theory that color vision depends on systems that produce opposite responses to light of different wavelengths. See Figures 10.25.
opsin
One of the two components of photopigments in the retina. The other component is retinal.
optic ataxia
A spatial disorientation in which the patient is unable to accurately reach for objects using visual guidance.
optic chiasm
The point at which the two optic nerves meet. See Figures 2.12, 10.10.
optic disc
The region of the retina devoid of receptor cells because ganglion cell axons and blood vessels exit the eyeball there. See Figure 10.1.
optic nerve
Cranial nerve II; the collection of ganglion cell axons that extend from the retina to the optic chiasm. See Figures 2.9, 10.10.
optic radiation
Axons from the lateral geniculate nucleus that terminate in the primary visual areas of the occipital cortex. See Figure 10.10.
optic tract
The axons of retinal ganglion cells after they have passed the optic chiasm; most terminate in the lateral geniculate nucleus. See Figure 10.10.
parvocellular
Of or consisting of relatively small cells. Compare magnocellular.
photon
A quantum of light energy.
photopic system
A system in the retina that operates at high levels of light, shows sensitivity to color, and involves the cones. See Table 10.1. Compare scotopic system.
photoreceptor adaptation
The tendency of rods and cones to adjust their light sensitivity to match ambient levels of illumination.
photoreceptors
Neural cells in the retina that respond to light.
primary visual cortex (V1)
Also called striate cortex or area 17. The region of the occipital cortex where most visual information first arrives. See Figures 10.11, 10.12, 10.19.
pupil
The aperture, formed by the iris, that allows light to enter the eye. See Figure 10.10.
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 a particular range of stimulus intensities. See Figure 8.6.
receptive field
The stimulus region and features that affect the activity of a cell in a sensory system. See Figures 8.9, 10.13, 10.15.
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.
retina
The receptive surface inside the eye that contains photoreceptors and other neurons. See Figures 10.1, 10.2.
retinal
One of the two components of photopigments in the retina. The other component is opsin. (The term is printed in small capital letters in this text to distinguish it from the adjective retinal, meaning “pertaining to the retina.”)
rhodopsin
The photopigment in rods that responds to light.
rods
A class of light-sensitive receptor cells (photoreceptors) in the retina that are most active at low levels of light. See Figure 10.2. Compare cones.
saturated
Referring to the condition in which a maximal number of receptors of one type have been bound by molecules of a drug; additional doses of drug cannot produce additional binding.
scotoma
A region of blindness caused by injury to the visual pathway or brain.
scotopic system
A system in the retina that operates at low levels of light and involves the rods. See Table 10.1. Compare photopic system.
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. Compare complex cortical cell.
spatial-frequency filter model
A model of pattern analysis that emphasizes Fourier analysis of visual stimuli. Compare feature detector model.
spectrally opponent cell
A visual receptor cell that has opposite firing responses to different regions of the spectrum. See Figures 10.25, 10.26.
striate cortex
See primary visual cortex.
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.
visual acuity
Sharpness of vision.
visual field
The whole area that you can see without moving your head or eyes.
wavelength
Here, the length between two peaks in a repeated stimulus such as a wave, light, or sound. See Box 9.1, Box 10.1.
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