Chapter 7: vision Flashcards
retina
turns light into neural signals through transduction
cornea
transparent outer layer; bends light rays through refraction and is primarily responsible for forming the image on the retina
lens
changes shape to fine-tune the image on the retina
accommodation
process where ciliary muscles adjust the lens to bring nearby objects into focus
myopia
(nearsightedness) difficulty seeing distant objects; eye grows to long
photoreceptors
sensory neurons that detect light (rods and cones)
rods
most active at low light and respond to visible light of almost any wavelength
cones
different varieties that respond differently to light of varying wavelengths: see color
bipolar cells
interneuron in the retina that receives information from rods and cones and passes information to retinal ganglion cells
ganglion cells
cells whose axons form the optic nerve (only ones that use action potentials)
optic nerve
carries information to the brain
horizontal cells
make contacts among the photoreceptors and bipolar cells
amacrine cells
contact both the bipolar cells and the ganglion cells
scotopic system
a system in the retina that operates at low light and involves rods but is insensitive to color; sides of the retina(periphery)
convergence
phenomenon of neural connections in which many cells send signals to a single cell
photopic system
high levels of light, shows sensitivity to color and involves the cones; found mostly in the fovea
rhodopsin
the photopigment in rods that responds to light and cause signaling chain that leads to hyperpolarization(photons=quanta of light)
pupil
deals with the large range of intensities by adjusting the size (and opening in the iris)
range fractionation
each sensory receptor cell specializes in just one part of the overall range of intensities
photoreceptor adaptation
each photoreceptor constantly adjusts its sensitivity to match the average level of ambient light
fovea
the center region of the retina has a high density of smaller, tightly-packed cones with high acuity
visual acuity
a measure of how much detail we see and is
sharpest in the center of the visual field.
optic disc
where blood vessels and ganglion cell axons leave the eye
blind spot
region on the retina that is sightless due to lack of photoreceptors in the optic disc
optic cortex
receives action potentials from ganglion cells
visual field
the area that is visible without movement of the eye or head
topographic projection
This organization is preserved as the information travels through the
brain
on-center bipolar cells
turning on light in the center of its receptive field excites the cells because it receives less glutamate, which inhibits this type of bipolar cell
off-center bipolar cells
turning off light in the center of the field excites the cells because they receive more glutamate and are depolarized
on-center ganglion cells
on-center bipolar cells excite when light is turned on
off-center ganglion cells
Off-center bipolar cells excite when light is turned off
lateral inhibition
sensory receptor cells inhibit information from neighboring receptor cells, producing a contrast effect at the edges of regions
simple cortical cells
(bar detectors/ edge detectors) respond to an edge or bar of a particular width, orientation, and location in the visual field
complex cortical cells
respond best to a bar of a particular width
and orientation that is in motion anywhere in the visual field.
spatial frequency model
the visual system analyzes the number of light-dark (or color) cycles in any stimulus
wavelength
color is perceived by the visual system as we detect differences in the photons within a certain range.
trichromatic hypothesis
Three different types of cones
* Each responds to a specific, different part of the spectrum
* Each has a separate pathway to the brain
* Color recognized based on which receptors are activated
opponent-process hypothesis
Four unique hues
* Three opposed pairs of colors
* Three physiological processes with opposed positive and
negative value are the basis of color vision
spectrally opponent cells
(color-opponent): have opposite firing responses to different regions of the spectrum
ventral stream
identifying objects (what)
o Damage causes problems in perceiving faces and
objects.
dorsal stream
assessing the location of objects (where),
and guiding our movement toward them
amblyopia
misalignment of the eyes; reduced visual acuity not caused by optical or retinal damage
* visual cortex suppresses information from one eye
*eye muscles can be surgically adjusted to achieve better alignment; and use weak eye regularly
