Vision Flashcards
Cornea
curved transparent external surface of eye, causes light to bend, no receptive field
Pupil
the Opening allows light to enter the eye, no receptive field
Iris-circular muscle
controls pupil size, no receptive field
lens
focuses the light of the retina, no receptive field
Ciliary muscles
control lens shape
Accomadation
process of lens changing to focus on different objects
Extraocular muscles
control eye movement
Retina
layers of cells at the back of the eye,
rods and cones(Spot of light)
bipolar cells(Concentric RF)
ganglion cells(Concentric RF)
axons of ganglion cells form the optic nerve
Rods and Cones(photoreceptors)
transduce light, spot of light
Two functional systems of Retina
Scotopic system, Photopic system
Scotopic System
functions in dim light, one type of receptor(rods)
Photopic system
functions in brighter light, three types of (cone) receptors
photopigment(captures light) in rods
rhodopsin
rhodopsin
composed of retinal and opsin
Photoreceptors Hyperpolarization
- light activates rhodopsin
- retinal dissociates from opsin
- opsin binds G protein
- G protein transforms 2nd messenger
- blocking Na+ channels causing hyperpolarization(and less glutamate release)
Cones Function
similar to rods but have three different types of opsin
on center bipolar cells
hyperpolarize in
response to glutamate from photoreceptors,
want light, meaning less glutamate
off center bipolar cells
depolarize in
response to glutamate,
want less light meaning more glutamate
photoreceptors and bipolar neurons in response to Dim light
lots of glutamate
off center has a large response,
on center has a low repsonse
photoreceptors and bipolar neurons respond to brighter light
less glutamate,
on center has a high repsonse
off center has a low response
on center bipolar cells excite
on center ganglion cells
off center bipolar cells excite
off center ganglion cells
fovea
depression in central region of retina best acuity
why does fovea have best acuity
no cell layers
the high density of cones
low cone-to-ganglion ratio
large amount of V1 devoted to fovea
Visual pathway
ganglion cells in retina
-optic nerve
-optic chiasm
-optic tract
lateral geniculate(thalamus(brain))
-optic radiations
occipital(or striate) ctx
extrastriate ctx
Receptive Field
stimuli in the environment (visual space) that increase or decrease the cells response
bipolar and ganglion cells in retina have
Concentric Receptive fields
on center/off surround
cell is excited by spot of light in its center
off-center/on surround
cell is excited by spot of dark in its center
Concentric receptive fields
response to light is opposite in center vs surround
Ganglion cell types
off center and on center, M cell(movement) and P cells(Pretty), concentric
M cells
larger RF
more sensitive to low-contrast stimuli
stimulus movement
P cells
the opposite of M cells
sensitive to form and fine detail
sensitive to wavelength
have color opponent property, center and surround are excited by different colors
have spectral opponency
Lateral Geniculate nucleus
concentric RF
Layer of cells
-parvocelluar neurons
-magnocelluar
Magnocellular and parvocellular layers reflect properties of input M cell and P cells
Parvocellular
receive info from P cell
spectral opponency
Magnocelllular
receive info from M cells
LGN projects to
Layer IV of visual of cortex by optic radiation(Axon RF)
Layer IV
left and right eye projections are laid out as a series of alternating bonds called ocular dominance columns
simple cortical cells
Respond best to an edge or bar of a particular width, orientation, and location
complex cortical cells
Respond to the bar of particular width and orientation anywhere in the visual field
two major systems of cortical visual areas
ventral processing stream
dorsal processing stream
Dorsal Processing Stream
where
location of objects
perception of place, depth, and movement
extension of magnocellular pathway(LGN)
MT(V5), MST, and other dorsal areas
Ventral Processing Stream
what
visual identification of objects
analysis of form and color
extension of the parvocellular pathway
V4, IT, and other ventral areas
Dorsal processing stream
V1—> V2—>V3—>MT(V5)—>MST—>other dorsal areas
Ventral Processing Stream
V1—> V2—> V4—> IT—> other ventral areas
V2
illusory contours(triangles)
MT
Perception of motion
V4
Intermediate complexity, ex. radial stimuli, ceiling fan
IT
complex forms and pattern recognition(faces)
cones for trichromatic theory
doesn’t respond to a specific wavelength
responds to a range of wavelengths and peaks at a particular wavelength
Small medium and Long
spectral opponency
One color excites the center; different color excites the surround
ex. Long wavelength excites, Medium wavelength inhibits
optic nerve
one eye two fields(left and right)
optic chiasm
two eyes two fields
optic tract
one eye, one field
spectral oppencey
