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; 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 on 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
extraocular 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 at 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 respond 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 off 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 with 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 cells 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 the blind spot cannot be seen
occipital cortex
also called visual cortex; the cortex in 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 chimes; 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 lateral geniculate that terminate in the primary visual areas of the occipital cortex
primary visual cortex (V1) or striate cortex
the region of the occipital cortex where most visual information first arrives; also called area 17
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 point-to-point correspondence between neighboring parts of 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 may still 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
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, also sensitive to motion
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 the three basic dimensions of light perception, varying from dark to light
hue
one of the three basic dimensions of light perception, varying around the color circle through blue, green, yellow, orange, and red
saturation
one of the 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 static 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
