Visual Perception 5 Flashcards
what is compromised in the theory of the conflicting cues
size perception
the converging lines give the perception of depth in a 2D image and the visual system assumes that a retinal image that appears to be further away will have a bigger physical size
the ponzo illusion
-tells us that this object must be more distant, same retinal size but appears more distant so it tell us that it must be bigger
what is the ames illusion
how is the visual angle related
what does the visual system assume
back wall shift and one person is closwer and one is more distance giving them a diff in size
both poeple have same visual angle
visual system assumes that the 2 poeple are at the same distance so one person appears larger and there is a greater visual angle
what are the 2 explainations for the Ames room
- size-dist scaling equation
2. relative size
what is the size-dist scaling equation explaination for the Ames room
the construction of the ames room cuases the person on the left to have a much smaller visual angle than the person on the right
-we perceive this distance as being the same bc of size-dist equation even though its not => 2 diff retinal img sizes => perception of size is diff
D is the same and R is diff and S is diff
what is relative size explaination for the Ames room
person on the right fills the whole room
bc we know that a normal size person wouldn’t fill the whole room so we perceive them as bigger
what is the moon illusion
the physicla size and dist of moon stays the same throughout the night => retinal image remians the same
- what chagnes is the perceived dist of the moon
- when the moon is closer to the horizon it is perceived as being further waway than when its a zenith (highest point reached)
why does the moon appear to be further away when its on the horizon
why does it appear to be shorter when its at zenith
bc we have depth info and we can judge the dist
at zenith we have no cues for depth and therefore we misperceive the dist as being shorter (bigger moon()
S=a(RxD)
what is the angular size contrast theory for the moon illusion
moon appears smaller when its high on the sky bc it is surrounded by a very big object (black sky)
what is the ebbinghaus illusion
circle surrounded by large circles look bigger bc of relative size
which illusions do not rely on prior knowledge but on physiology alone
- the hermann grid illusion
- mach bands
- simultaneous contrast
what is the hermann grid illusion
you see dark circles appearing at the intersections
- explained by lateral inhibition (influence of neurons on surrounding neurons)
ex. center-surround receptive field=inhibition - more inhibitions when looking at the intersections than when not
why don’t we see the reduction of lateral inhibition when we fixate at an intersection
prob cuase the bipolar cell receptive filed size is small enough so it doesn’t receive strong inhibitroy input from many surrouding neurons
what is the scintillating grid illusion
a bright spot appears darker at an intersection when you move your eyes around it
lateral inhibition
what are mach bands
stripes of dark and light created at the border of a dark and light surface
-appear as light enhancements at the light side of the border and dark at the dark side of the border
what can mach bands be explained by
lateral inhibition
what is simultaneous contrast
the effect a surround has on the apparent brightness of an object
why does the square with the light background seem lighter
ligher surround=>greater lateral inhibition=> center appears dimmer
is lateral inhibition a satisfactory explaination
yes bc it explains in general the perceptual effect
no bc it fails to explain why the cetners of the squares dont look birghter or darker than the border of the squares
why can white’s illusion not be explained by lateral inhibition by the way explained mach bands and hermann grid illusion
the one on the right should receive stronger lateral inhibition bc they’re surrounded by white and SHOULD appear darker but don’t bc of beloningness
how can belongingness expalin white’s illusion
left rectangles belong to the white background and the right rectangles bleong to the black stripes
=> the amount of inhibition is dictated by wehre they belong
=> less lateral inhibtion from black background so appears brighter
what is it called when phenomena have to do w/ a strucutre or property that is in our eyes
entropic phenomena
why can we not observe the purkinje tree
bc of adaptation
what are henle’s fibers
the photoreceptors have axons that connect the photoreceptor inner segments w/ bipolar cells
the axons are called henle’s fibers
what kind of properties do henle’s fibers have
polarizing properties
what kind of light does macular pigment absorb
short wavelenth of ligh
how will the light appear at the areas w/ abosoption, w/o absorption in haidinger’s brush
w/ = yellow w/o= blue
where are the haidingers brushes only visible at
macula
what is the central black spot that appaears at the center of the vf when blue light is seen?
what is it due to?
maxwell’s spot
- due to macular pigment absorbing short wavelength light
- when macular conc is high, more short wavelenth light is absorbed and therefore less light transmitted => black spot
maxwells’ spot can be measured to estimate the ___ and ____ of macular pigment
topography
optical density of macular pigment
what are phosphenes
lights or dark spots seen w/o any light stimulation
what are electrical phosphenese caused by
electrical stimulation in the brain
-magnetic field applied at the visual cortex, phosphenes will be perceived
transcranial magnetic stimulation has been reported on produceing….
visual prosthesis uses…..to elecit perceptual responses
phosphenes
what are muscae volitantes
floaters
what appear in case of vitreous detachment usually at the temporal visual field (nasal retina)
usually follows the outline of the vit detach
dangersous cause could lead to retinal detach
moore’s lightening streaks
why do flying spots happen (blue field)
white blood cells circulate w/in the retina
blue light is absorbed by RBCs but not but WBCs
-WBCs create disruptions in otherwise uniform vessels that are filled w/ rbcs
what is the dark light or eigengrau
not complete darkness but we perceive it in the absense of light
dark grey background=>spontanteous neural noise that is always present w/in the visual system
due to under-sampling of the cone mosaic we can’t distinguish gratings above the nyquist limit, what is this known as
aliasing
