Vision Flashcards
what do we see
The reflection of electromagnetic waves emitted by the sun; color is the absorption of all wavelenghts exept those
optic nerves from the left and right eye partially cross at the …
optic chiasm
rods
perception at very low levels of light
cones
perception at a lot of light: colors and details
difference rods and cones regarding photons
rods can be triggered by a single photon, cones need to absorb more photons
fovea
Place on the retina where the image you focus on is projected to.
hoe gaat het signaal vanaf retina naar optic nerve
photoreceptors -> 5 other cell layers: bipolar cells - ganglion cells -> via optic nerve that goes through the retina, creating a blind spot
waar zijn de rods en waar zijn de cones veel
cones veel bij fovea, rods veel buiten de focea
acuity
hoe scherp het is: hoogste bij de fovea, wordt minder hoe verder je er vanaf gaat
je hebt alleen een duidelijk en kleurrijk beeld bij de fovea, de rest is wazig
maar dit zie je zelf niet zo!
saccades
we constantly redirect our gaze (3/4x per seconde) -> niet random maar to salient events
subcortical visual processing
Retina -> optic nerves -> optic chiasm -> optic tracts -> lateral geniculate nucleus (LGN) in thalamus -> optic radiations -> primary visual cortex
LGN 2 components and what do they receive
- parvocellular system: from retinal parvocellular ganglion cells
- magnocellular system: from retinal magnocellular ganglion cells
parvocellular
Small conduction velocity
-
Some are color sensitive
-
80% of retinal ganglion cells
magnocellular
large receptive fields
(input from many
-
Fast conduction velocity
-
Info about motion and
depth to visual system
-
No color information
-
10% of retinal ganglion
cells
opbouw van LGN
6 - L - P
5 - R - P
5 - L - P
3 - R - P
2 - R - M
1 - L - M
optic radiation
axons from the LGN project to the primary visual cortex
retinotopic organization at thalamus and V1
Objects that are close to each
other in the visual field (and
hence the retina), are also
represented close to each
other in the primary sensory
cortex.
cortical magnification
the size of unit area in the retina =/= visual cortex representation -> fovea neemt veel meer ruimte in beslag.
cortical modularity
cortical columns in primary sensory areas. (bv: ocular dominance colomns: reageren liever op een oog dan op de andere)
receptive field
region in the retina that evokes a response in the neuron being measured.
a neuron in V1 receives input from multiple LGN cells
oke
LGN cell gets active when a light shines on it, but immediately inactive when a light shines beside it.
oke
The further you go in the
visual stream, the more
complex the receptive fields!
(simple cells vs complex cells (grandmother cells))
dorsal stream
where -> motion and spatial, to parietal
ventral stream
what -> form and color, to temporal
ezelsbruggetje voor streams
venTral - whaT - Temporal lobe
visual processing properties
lightness/brightness
color
form
depth
motion
Simultaneous lightness/brightness contrast
phenomenon
patches have the same luminance but you experience them as different colours.
- door lateral inhibition: patch with darker background will be perceived as lighter, due to contrast. patch with lighter background will be less active due to lateral inhibition. (light = inhibition of surrounding cells!)
Maar… dit is niet helemaal zo, want het ligt ook vooral aan onze kennis van de wereld.
Dus; door de inverse problem: many different sources can produce the image on our retina.
3 qualities of color
- hue = color
- brightness = fel
- saturation = colourness (grey of meer kleur)
verschillende cones
3! (short, medium and long wavelengths.)
color contrast
patches with identical physical properties can be seen as very different colours.
color constancy
patches with different physical properties can be seen as the same colour
which area processes colour
V4
damage to V4 leads to
cerebral achromaoopsia (alles in zwart wit)
form
perception of line lengths, orientation and intersections
Does activity in V1 correspond to the actual
stimulus or the perceived stimulus?
No, the activation evoked by the stimulus
corresponded to the subjective experience
of the size, not to the actual size.
monocular components
- size and depth relative
- occlusion
- motion parallax (ver gaat met je mee, dichtbij gaat er tegenin)
binocular component
retinal disparity because our eyes are further apart -> creates a different picture
binocular rivalry
each eye gets a completely different image. but it is not a combination between the two, but a continuous change between the two states!
motion
processed in area V5 wss
aperture problem
Many combinations of speed
and direction can give rise to the sequence of
images falling on the retina -> hoe???
apparant motion
Two static stimuli that are
presented in close succession create a sense of
motion. Known in Gestalt psychology as the phi
phenomenon.
motion aftereffect
After staring at motion to a
single direction, you can observe motion in the
opposite direction when looking away from the
motion (neural adaptation?)
You don’t need visual input to get visual cortex
activity!
Visual imagery of an object suffices to recreate the
activity pattern in the visual cortex that would be
active when seeing the object.
bv bij denken aan stoel.
retinal ganglion cells
in LGN!!! -> parvocellular and magnocellular
volgorde outside eye
sclera -> choroid -> retina
