Vision: Visual Processing Flashcards
(25 cards)
optic nerve
axons from ganglion cells
optic chiasm
axon from nasal hemiretina cross over to the other side of the brain. hemiretina recieves image retinas from the opposite visual field
optic tract
radiation of fibres into brain from optic chiasm
lateral geniculate nucleus
part of the thalamus
occipital cortex
primary visual cortex, also called striate cortex. inputs from both eyes converge to give binocular vision
retinotopic organization
map of retina maintained at all levels and projected onto visual cortex. other areas also receive visual inputs: superior colliculus and suprachiasmatic nucleus
parvo
four outer layers of the LGN contain small parvocellular neurons. they have relatively small, donut shaped receptive fields and sensitive to wavelength. recieve axons from P type retinal ganglion cells
magno
inner 2 layers of the LGN contain large magnocellular neurons. they have larger receptive fields and most arent sensitive to wavelength. recieve axons from M type retinal ganglion cells
area V1: visual cortex
primary visual cortex, first stop in processing. there are 4 classes of v1 cells:
simple, complex, hypercomplex I , hypercomplex II
simple v1
bar or edge of specific width, orientation and location of visual field
comples v1
elongated receptive fields. bar or edge of specific orientation but could at different locations
hypercomplex i v1
particulat emphasis on bar length
hypercomplex ii v1
particular angles of intersection of lines
initial theory v1
vision was heirarchical and successively higher levels responded to more complex stimuli
problem to the initial theory v1
theory implies that the top of the heirarchy has cells that responded only to stimuli that are unique to the world. we have far too few neurons for the visual system to work like this.
cortical blindness
a place in the visual field in which nothing is perceived visually
blindsight
other brain regions can permit some perception of movement even if theres no conscious perception of objects
area V2
recieves input from v1, has more complex receptive fields and is active in providing contour inferences, which is important in disemedding stimuli. has complex interactions with V4 and passes information to the temporal lobe
disembedding
discriminating which parts of the visual scene make up items
area V3
involved in dynamic form where objects in motion keep shifting appearance, but visual system doesnt need to keep disembedding it
area V4: colour perception
composed of two theories: trichromatic theory and opponent process theory, which were both right
trichromatic theory
sensitivity to 3 colours would provide colour vision -RGB
opponent process theory
balance in 3 opposed dimensions could provide colour: blue-yellow, red-green, white-black
4 types of LGN cells
+L / -M: orange red 650nm
+M / -L: blue green 500 nm
+(L + M) / -S(L + M - S): far red 700 nm
+S / -(L + M)(S - L + M): blue 450 nm
