week 11 (vision) Flashcards
(28 cards)
explain: types of bipolar cells in foveal cone (2)
-
OFF bipolar cells
- hyperpolarized by light
⤷ like photoreceptors -
ON bipolar cells
- depolarized by light
explain: types of retinal ganglion cells (2)
-
P
- receives info from midget bipolar cells (fovea)
- most numerous
- high density in fovea
- projects to parvocellular LGN layers
- small -
M
- receives info from diffuse bipolar cells (periphery)
- projects to magnocellular LFN layers
- large
question: what was found about retinal ganglion cell behaviour from the cat exp? (kuffler)
- retina detects diff. in light in adjacent parts of retina
- flooding retina w/ light doesn’t change spont. firing
explain: receptive field of retinal ganglion cell
- area of the retina/vis field that influences the neuron
⤷ can be excitatory or inhibitory - excitatory zone + inhibitory zone = center surround antagonism
explain: responses of an ON-centre ganglion cell to light (4)
- light in center = firing rate increases
⤷ center of an ON-center = excitatory - light in center and a bit of surround = firing rate faster
⤷ surround isn’t fully illuminated so center input dominates - light in centers and full surround = firing rate slows
⤷ surround exerts inhibitory effect
⤷ cancels some of excitatory - diffuse light = no effect on firing rate
⤷ uniform illumination -> no contrast
⤷ RGCs detect diff. in light
define: centre-surround antagonism and lateral inhibition
- centre-surround antagonism = two subregions of the receptive field oppose each other
- lateral inhibition = antagonist interaction between center and surround
name: consequences of centre-surround effects (3)
- lightness contrast
- lightness constancy
- mach bands
explain: lightness contrast
- lightness of an object appear to be altered when different backgrounds
- center is affect by surround
- ex. things on a darker bg look lighter
⤷ bc contrast is greater
⤷ on a graph: neural resp. fires more for darker at all light intensities
explain: lightness constancy
- overall change in ambient illumination affect both center and surround
- change in light intensity affects both equally -> looks overall lighter
- ex. on a graph: changing light intensity (x axis) -> same change for both light or dark bg
explain: mach bands
- bands go from dark to light moving L to R
- false impression of a narrow dark band immediately to the L + a narrow light band to the R of each boundary
RGC AT R EDGE
- center = dark
- surround = partially dark
- fires above baseline
⤷ part of inhibitory (surround) = lit, but none of center = lit
⤷ overall lower firing -> makes fake dark band
RGC AT L EDGE
- center = light
- surround = partially light
- fires above baseline
⤷ entire excitatory (center) = lit, but only part of inhibitory
⤷ overall higher firing -> makes a fake light band
**bands where all of inhibitory and excitatory are same -> dep. on if in light or dark region
question: how do eye doctors measure visual acuity?
- snellen chart
- visual acuity = distance at which person can just ID letter / distance at which normal person can
⤷ legal blind = 20 / 200 (what avg person can see at 200ft away, you need to be 20ft away to see)
question: how do vision scientists measure visual acuity?
- measure the smallest visual angle of a cycle of grating that can be perceived
- visual angle = angle of an object to the retina
⤷ smallest resolvable gratings = 0.017 degrees
⤷ 1 cm = 1 degree of visual angle (at 57cm distance)
define: cycle and contrast of a grating
- cycle = one repetition of a black and white stripe
⤷ trough of a wave = black/dark
⤷ peak = white - contrast = diff. in illumination between object and the bg
⤷ or between light and dark parts of an object
question: what determines resolution acuity?
- spacing of photoreceptors in the retina
- ex. gratings
⤷ perceiving the grating = whitest and blackest parts are place on distinct cones
⤷ if one cycle falls on one cone -> gray
⤷ need two cones per cycle to see a grating
explain: contrast sensitivity function
x axis = spatial freq.
L y axis = contrast sensitivity
R y axis = contrast %
- contrast threshold = smallest amount of contrast needed to detect a pattern
- Nyquist limit = highest spatial freq. that a photoreceptor array can theoretically sample
⤷ determined by cone spacing
compare: low, right, high spatial freq. for gratings
LOW
- center = falling on light and dark
OR
- center and surround fall w/in one fat stripe
- no diff. than baseline
RIGHT
- center = all light, surround = all dark
- can observe the grating pattern
HIGH
- center = falling on light and dark
⤷ too many cycles in one RGC
- on diff. than baseline
name: pathway projecting from retina to visual cortex
- retinogeniculostriate pathway
- passes retina
- to lateral geniculate nucleus (LGN)
- to striate cortex/primary vis. cortex (V1)
question: what path does information from the inner R visual field follow to reach the V1?
R INNER VISION
- L temporal retina
- down optic nerve
- down R tract
- to L LGN
- to V1
question: what path does information from the outer L visual field follow to reach V1?
L OUTER VISION
- L nasal retina
- down optic nerve
- crosses optic chiasm
- down L tract
- to R LGM
- to V1
question: what part of the visual path crosses the optic chiasm?
- nasal information
⤷ comes from the outer parts of the visual fields
question: optic tract vs optic nerve?
- tract carries info from 2 eyes
⤷ but the same visual field - nerve carries info from same eye
⤷ but from diff. visual fields
explain: LGN structure
- lateral geniculate nucleus
- 6 layers
⤷ 1 - 2 = magnocellular
⤷ 3 - 6 = parvocellular - koniocellular layers = in between each layer
⤷ for blue yellow
explain: ventriloquism effect
- sound info from a person assoc. w/ vis. info of a puppet
- multisensory
- simultaneous but spatially discordant input
⤷ induces translocation of the sound to the vis input
⤷ bc vision tends to dominate (bc higher reliability)
name: example where sight doesn’t win over sound
- two-flash illusion
- play 2 beeps but show 2 flash -> perceived as two flashes
- aud. = better for temporal
⤷ trusts aud. -> thinks it’s 2 flashes when its only 1
