Perception Final Exam

light

electromagnetic energy

visible light

one part of the electromagnetic spectrum

wavelength

corresponds to perception of color

amplitude/intensity

corresponds to perception of brightness

vision ______ require a medium

does not

a wavelength with more energy (higher amplitude) is going to be perceived as ____

brighter, regardless of color

the visual system is divided into _____

left and right side

when do the left and right side get rejoined?

in the high visual cortex

what are some things we need to be able to do to accurately perceive the world around us?

- pupil opening or closing (dealing with light or dim situations)
- focus at a distance

pupil description

- opening at the front of the eye that lets light in
- can dilate or contract to let more or less light in

iris description

the opening around the pupil where the color of your eye is

lens description

- one of the two structures responsible for focusing the light
- bends the light so it lands where you want as you focus there

cornea description

- outer most layer
- light passes through cornea then the pupil
- with the lens, it is responsible for focusing the light
- bends the light so it can reach the retina correctly
- first point where it starts the light (fixed amount, 2/3 of our ability to focus), then the lens bends it further (to adjust and fine tune it)

retina

- light reaches this
- surface on the back of eye
- contains the photoreceptors which are actually responsible for light detection
- where the sensory receptors are
- this is where the lens, cornea and pupil all get to the signal to

pupil size

adapts depending on the amount of illumination (darkness = dilates, brightness = contracts)

zonules of zinn

attached to your ciliary muscles which are around the lens and can push and press the lens or relax to let the lens relax too

what does pushing the lens do?

increase the power when you need to focus on things up close because the harder the muscles are pushing the lens, the better your ability to see up close

accomodiation

- the ability to bend the light to adjust for different distances
- allows power of lens to vary

accommodated lens

ciliary muscles are contracted and lens is bulging out, zonules of zinn are relaxes

unaccommodated lens

lens is thinner and ciliary muscles are relaxed, zonules of zinn are contracted

accommodation ability ___ with age, why?

decreases because lens becomes harder (presbyopia)

presbyopia

losing the ability to see close (because of age)

measure of your accommodative power

how close you can focus (decreases as you get older)

myopia

- near sighted
- eyeball is too long so light from the same location will strike different parts of the retina which will then be perceived as blurry

hyperopia

- far sighted
- eyeball is too short meaning focusing point is beyond the retina so when light hits the retina, they're not focused
- insufficient accommodation

why don't people always notice they are hyperopic?

because the ciliary muscles are always doing work and so if you are young, you can do that and so they don't always notice they are hyperopic as long as they can accommodate

what does 20/20 vision actually mean?

- only a measure of your distance processing
- so 20/20 means that at 20ft you can see the same sized letter that an average person can see at 20ft

astigmatism

- non-spherical cornea

spherical cornea

will bend light the same way no matter what direction it's coming from

non-spherical cornea

can cause weird distortions so some of the light gets bent more than others depending on what direction its coming from

fovea

central point at which you are focusing

optic disc

there are many blood vessels that supply blood to the cells in the retina and to the fovea, but they have to enter somewhere which is the "blind spot" which is the point in the eye where you cannot see, aka the optic disc

two types of photorecptors

- rods
- cones
- both are responsible for detecting light and fire when photons strike them

three types of cones

- long, medium and short wavelength cones

temporal

towards outside of head (left part of the left eye)

nasal

towards nose (right part of the left eye)

on the periphery there are ___ cones then it spikes in the ____

less cones then it spikes in the middle

cones are responsible for

giving us the ability to distinguish different colors (rods don't do that)

fovea is the ___ of our vision

center, rods drop to zero and we have only cones there

if we have more cones packed together tightly vs less of them spread out, how does that effect the ability to detect light at different parts of the retina?

it improves our ability to detect light at the fovea because there are so many - not as effective in the periphery

why can we still perceive color in our periphery since there are not many cones?

- our perception of the world is continuous in color because we fill in that information (similar to how we fill in our blind spot from optic disc so we don't notice it)
- our brain assumes based on the details we know
- on average, we move our eyes 4 times a second so we are taking in a lot of color information which builds a perceptual representation of where we are - so that when we are looking at just one location, it assume that the information it has of your surroundings is staying the same

horizontal and amacrine cells

- receieve information from multiple photoreceptors
- important for ON-/OFF- center receptive fields
- these are cells in the retina

bipolar cells (two types)

visual periphery and fovea

visual periphery bipolar cells

diffuse bipolar cels recieve information from up to 50 receptors (mostly rods)

fovea bipolar cells

midget bipolar cells receive information from single cones

each cones connects to ___

two types of bipolar cells (primarily in the fovea) - ON bipolar cells and OFF bipolar cell

ON bipolar cells

fires action potential when the photoreceptor activates aka when it detects light

OFF bipolar cells

firing action potential even when there is not light, when there is light it stops firing

ganglion cells (two main types)

P ganglion and M ganglion

P ganglion cells

(70% of the total ganglion cells)
receive information from midget bipolar cells

M ganglion cells

(10% of total ganglion cells)
receive information from diffuse bipolar cells

two general pathways in the retina

1. rods -> diffuse bipolar cells -> M ganglion cells
2. cones-> midget bipolar cells -> P ganglion cells

explain rods to diffuse bipolar cells to M ganglion cells pathway

- multiple rods connect to individual bipolar cells so better sensitivity but poorer acuity
- very sensitive even to low levels of light, but lose sensitivity to small differences spatially
- periphery

explain cones to midget bipolar cells to P ganglion cells pathway

- individual cones are connecting to individual ganglion cells so high acuity but much poorer sensitivity (why it's so hard to read in the dark)
- fovea

there is a ___ tradeoff between periphery and fovea

acuity-sensitivity

luminance levels

- what kinds of light levels correspond to different things
- different thresholds for different photoreceptors

absolute threshold for any light is based on what?

response of rods and it is very sensitive

best visual acuity is around ____

indoor lighting

rods have ____ threshold in dark

- lower

explain how you can adapt to the dark and why you can't see colors as clearly

- vision improves the longer you are in the dark
- 20-30 minutes for someone to fully adapt to a dark environment coming from a light environment
- cones bottom out, however, they hve a higher threshold (poor sensitivity) in dimly lit environments
- rods however will keep adapting and you will be sensitive mostly based on the response of the rods
- this is why we cannot easily see color in the dark - we are relying rods which do not give us color information like cones do

ON-center OFF-surround ganglion cell

- when light is presented in the center of the area that the ganglion cells is interested in, it will fire
- like when there is light in the center and darkness around
- light turns on - it stars firing action potential
- if the spot of light is moved out of the middle, there is light in the periphery, that a pattern that it is not happy with so it will fire less action potential

OFF-center ON-surround ganglion cells

- would fire action potential more when light is not in the center, but in the periphery

ON-center and OFF-surround receptive fields

- if the light fits perfectly in the middle, the ganglion cell with fire the most

will the left or middle have a higher firing rate?

- the left will have a higher firing rate (you should add up the pluses and minuses)
- so the left and right will have the same firing rate since the pluses and minuses cancel out
- the middle is less than the left because there is a minus in the light

hermann grid

- at the intersection you have some receptive fields that are ON-center OFF-surround so that at the intersection its getting extra information from the edges
- the receptive fields make these illusory dark squares

when the spatial frequency gets higher, will the cones give information about each bar or will it blur together?

it will blur - not enough cones - they are all conveying the same information

low spatial frequency

can piece together the picture because there are enough cones that are spread out to convey information (at really high spatial frequencies, it's too fine of a difference for us to distinguish)

threshold gets ____ at extreme spatial frequencies compared to the middle ranges

worse

receptive fields are sensitive to?

what the spatial frequency is and the phase (where in the waveform it is)

selective adaptation

- you adapt one type of cell to sort of fatigue it
- for example, you have a bunch of receptive fields that like medium spatial frequencies - we can wear them out temporarily by showing you a grid of only those medium spatial frequencies

spatial sensitivity

- different spatial frequencies are what allow us to detect edges
- sensitivity to different spatial frequencies allows visual system to detect properties of an image
- image is composed of a sum of sine waves at different frequencies

in v1 there are __ and ___ cells

simple and complex cells

the ____ and ___ have to be aligned in a certain way to have more responses from the simple and complex cells

the stimulus and receptive fields

end-stop cells in V1

- when the stimulus width is exactly the width of the receptive field, there is maximum response from the cells
- the width of the stimulus sometimes matters

two types of column in V1

ocular dominance and orientation

orientation column in V1

- has clusters of cells that respond to different orientations
- each column has a different orientation

ocular dominance columns in V1

- whether it prefers information from the left or right eye

hypercolumns (in V1)

where orientation and ocular dominance columns are mixed together - so there is a left-eye ocular dominance slab with orientation columns within it and same for the right eye

what kind of stimulus does V1 simple cell like to respond to?

- edges in a particular orientation and location (if you move it or keep it but change the orientation, the simple cell will stop firing)

what kind of stimulus does V1 complex cell like to respond to?

- cares more about orientation than location
- independent of where in the retina they are being stimulated
- but dependent on orientation

the dark circular opening at the center of th eye, where light enters the eye

pupil

retina cells called ____ leave the eye via the optic nerve and transmit information to brain and midbrain

ganglion

which stimulus would optimally activate OFF-center ON-surround ganglion cell?

a shadow in the center of the receptive field (like dark in the center and light around)

low level vision

everything from light entering the eye to V1, it solves how to detect edges

after information leaves V1, what are the two basic paths it follows?

ventral (occipital to temporal love) or dorsal (occipital into parietal lobe)

ventral is known as ___ pathway

"what" pathway, it cares about shape, size

dorsal is known as ___ pathway

"where" pathway, it cares about where it is in space, how far away it is

edge detection by V2 cells

border ownership, edge detection relative to objects

border ownership

the idea that an edge is attached to the border of an object

good continuation

objects in the world have edges that continue even if an object is blocking them (i.e. a marker blocking an area of a paper - we know the edge is still there)

our brain fills in perceptual information using ____ as information

past experience (we assume objects will continue to have the properties they have had)

gestalt principles

grouping rules for object recognition - good continuation, similarity, proximity

good continuation (gestalt principle)

- if a marker is covering the edge of a paper, it is most probable that the paper continues behind it and isn't cut out randomly there
- doesn't always work

similarity (gestalt principle)

- things that are similar in shape, color, texture, size are a reason that objects would be grouped together
- so things that are different give us indication that they could be two different entities

proximity (gestalt principle)

- things that are closer together in space are more likely to be part of the same object
- ex. the different parts of one marker are closer that if there were another marker next to it

why do gestalt principles not always lead to accurate information?

- can be used to create camouflage
- ex. how animals use their environment to blend in

ambiguous figure

a visual stimulus that gives rise to two or more interpretations of its identity or structure

reversible figure

A drawing that is compatible with two interpretations that can shift back and forth

necker cube

- ambiguous in the sense that has two possible things that it could correspond to but the image doesn't tell us which one
- reversible because you can switch from one interpretation to the other

explain fatigue with necker cube (and other illusions/figures)

- if you perceive the necker cube one way, the neurons that are perceiving it that way start to fatigue so then it switches to the other perception
- through time, the system starts to switch quicker and quicker from A to B