Intro to visual perception Flashcards
History - Extramission
-reached out of your eyes + you touch things through your eyes
History-Democritus
-realised vision was occurring in the brain
-subtle atoms come from object into eyes
-see by eyes alone
-visual carter sees, eyes are just the way in
-visual images are burned
-vision is a relative not absolute sense-depends on context
History-Plato
-Actively opposed of experiment
-vision is very complicated
- can’t predict now things will look
- no one will ever be able to explain it
-resulted in no experiments done for hundreds of years
History -Alhazen
-Did experiments
-drew accurate anatomical eyes
-light rays coming off an object carry info to you
-light travels in a straight line
- while light composed of many colours
History-Leonardo da Vinci
- To make his paintings good had to understand how light works
- As things go far away become less saturated
-first view of real eyes
-very accurate drawing
-understood anatomy not physics of eye
History-Hermann von Helmholtz
-invented numerous things for looking into eye
- can’t look at someones eye because you need light to see and you block it when looking at someone
-look through telescopes with 2 lights placed nett to head that bane oft mirror + into eye
-Able to see balk of eye
-invented ophthalmoscope
since Helmholtz
-visual system is most studied understood part of brain
-provides quantitative, experimentally -verified link between changes in cells of the eye how we see
Iris
-muscle to expand + contract to control amount of light entering
Anatomy
- correa = main lens
-Aquas humour: fluid in anterior chamber
-iris = muscle
-pupil = hole in iris - ciliary body = makes aqueous humor
-ciliary muscle = controls lens shape
-virous humour = jelly between lens retina
Travelling light
-light comes from bottom
-cones + rods send signals to lots of cells
-cascade of info travelling to ganglion cells
-very complicated
-wiring under photorecepters act as little computer
-light enters retina is processed + computed rich signal is sent to brain
- L, M + s rods
-rods operate at night
- cones operate when there is more light
The fovea
-foveal pit formed by ganglion cells pulled back to help us see better
-gives photorecepters unimpeded view of world so central vision isn’t impacted by cell presence
- This is where all high resolution vision is so very little short wavelength because it is densely packed
- No rods in central - used to see in daytime
-no blue cones (short wavelength)
- more red than green cones
-red- long wavelengths
Rods
- more sensitive to light than cones
-provide low-resolution blurry black + White night vision
-cores give you sharp colour vision in light - Because there are no rods in the ford you can’t see things you directly look at in the dark
-Rods peak as you move away from centre
Adaptation- photoreceptors adapt to the average light
-if you KeeP something in the same place on your retina, photoreceptors adapt to it + it becomes harder to see
- prolonged fixation causes disappearance because photoreceptors constantly ask What is the normal thing + need to adapt to local env
-photoreceptors first see difference but don’t like it so change sensitivity so cant see difference
Adapt- photonreceptors respond to lights of different intensities
-schnapf et al 1990
- Although light pulses increase linear, gap between lines on graph are not constant
-once a photoreceptor is adapted, you flash light at different intensities
-response depends on adaptation state
where is the blind spot?
- 15 degrees from centre (fovea)
what do you see in your blind spot?
-Blind spot doesn’t look like a hole
- it is hard to see even with 1 eye closed
-Brain makes stiff to fill it in
-Brain makes up most of your visual field
Recording from cells in the retina
-mountcastle, Kuffler, Barlow
- Bright bar moved ground on screen
-electrodes placed in an anathetised cat brain
-electrons are in contact with 1 + neurons in the visual cortex
-experimenter waves stimulus around until finch place that stimulates neuron
- Amplifier takes signal from cortex + increases them to display on screen
-Neuron only responds when centre is illuminated indicates visual field it detects
receptive Fields
-on-centre RF may pool from signals on the retina
-Array f core cells contribute to whole RF
-Different sub-regions of RF
-signals from centre core are pod
-signals surrounding are neg
-Ada them = output that’s sent from retina to brain by ganglion cells
receptive fields overlap
-photoreceptors can provide excitatory input to 1 RF+ an inhibitory to another
-indiv cones contribute to different RF
-RFs can have excitatory and inhibitory regions
-Rs can be on or off centre
-on centre like while spots on dark background
-Bottom lines dark on white
Lateral inhibiton
-in the Rf the surround inhibits the centre
-Antagonism between neighbouring region is known as lateral inhibition
- Neg surrounds interact with pos centre
can we see the effects of RF’s Hermann
-Hermann + scintillating grid
-one Rf is positioned over a junction
-receives bright input to centre + surrounding
-Rf can be between lines receiving input to centre less on sides
why do we have RF?
- respond to structured inputs
-Pattern matching
-ignores changes in average brightness
-Turns visual world into an invariant code: contrast - combo of light adaption + RF (ganglion cells) lets us extract a constant representationof the world
Myobia -short sightedness
-exposure to outdoor light can welp prevent short sightedness
-eyeball is too long
