1
Q
perception
A
- interpretation of nerve impulses
- unconscious inference (all done by brain)
2
Q
plasticity in visual processing
A
- allows for development/adaptation
- ability to alter motor coordination as bodies grow, age, and learn new skills
3
Q
prism goggles: passive vs active adaptation
A
- passive: flipping book upside down
- active: interacting with the environment
4
Q
study: made participants wear prism goggles for a few hours. they had to point at something. 0 error without goggles. what happened?
A
- goggles on: they were way off target
- after couple hours: the active adaptation had some errors, but were way better
- after couple hours: the passive adaptation had less errors, but worse off than active
- thus, active adaptation is better bc they actually interacted w/ environment
- after taking goggles off: start making errors in the opposite direction. the group saw the world upside down AFTER taking goggles off and saw it regular while they were on bc their brain adapted to NOT flipping the image
5
Q
what is seeing with your brain shaped by?
A
interacting with environment
6
Q
how much can the fovea see?
A
- size of thumb
- everything outside of that is fuzzy
- bc we have eyes that constantly shift, but the picture is stable
7
Q
if we move eye with our finger, wht happens?
A
- the image shifts
- bc there is no muscle movement by eye, so brain assumes that we moved
8
Q
picture of spheres and cavities. two rows, each shaded same way. we only see one row as one of those things. what does our brain assume?
A
- that there is a single light source
- interprets light source as coming from above (second image has light shaded top to bottom)
- if we turn our head upside down, we see the opposite (second image)
9
Q
dots representing major moving points of person. wht can we determine? can kids do it?
A
- biological motion reveals sex and physical traits (size)
- emotion
- kids: can determine sex and physical traits BUT emotion is harder
10
Q
patient TN: series of strokes, damage to V1 but everything else was fine.
A
- he was functionally blind
- showing him pics of faces: he doesn’t know what he’s looking at. BUT if there was a scary face there, he would flinch. and he didn’t know why he flinched.
- EMOTIONAL BLINDSIGHT: emotion rxn to stimuli we can’t see
- when he walked down a hallway littered w/ random stuff: he was able to navigate through hallway even though he sees black
11
Q
humans with fourth cone
A
- tetrachromat
- exists in women more
- theory as to why women are more sensitive to colour
12
Q
where does visual perception come together
A
the brain
13
Q
which side of the brain are the right and left halves of our visual fields processed by? how?
A
- contralateral side
- opposite side
- axons on inner nasal region of each retina (region of retina closest to nose) cross over to opposite hemisphere
14
Q
optic chiasm
A
point where optic nerves from inside half of each eye cross over to opposite hemisphere
15
Q
where do axons from the outer temporal regions stay in respect to the brain?
A
same hemisphere
16
Q
does each hemisphere receive info from both eyes?
A
- yes
- bc visual field sends info to both eyes = each hemisphere gets info from both eyes
17
Q
what happens after info from each visual field arrives in opposite field after the optic chiasm?
A
- optic nerve splits and travel along two pathways
- collected bundle of axons are called the left and right optic tract
18
Q
what do optic tracts contain?
A
information ONLY from the contralateral visual field
19
Q
what is the part of the thalamus that receives visual information?
A
- LGN
- lateral geniculate nucleus
20
Q
LGN (lateral geniculate nucleus)
A
- part of thalamus tht receives visual information
- where most retinal and ganglion cell axons on the main pathway of the optic tracts synapse
21
Q
where do visual signals go after the LGN/thalamus?
A
- occipital lobe
- occipital lobe = primary visual cortex
22
Q
how many cortical areas process visual information? which one is extremely valuable?
A
- over 20
- area V1 of occipital lobe
23
Q
area V1 of occipital lobe is also known as…
A
- primary visual cortex
- striate cortex (bc it has stripes)
24
Q
what are the areas outside of the striate cortex/V1 called? wht do they do?
A
- extrastriate cortex
- further divided into areas V2 to V5
- colour/motion/object recognition
25
information from V1 is sent to…
- extrastriate cortex
- splits into dorsal and ventral streams
26
dorsal and ventral streams
- dorsal: “where pathway” bc it processes where objects are/their depth/their motion. goes to parietal lobe
- ventral: “what pathway” bc it processes what the object is, colour/form. goes to temporal lobe.
27
what is the receptive field of a single LGN cell made up of? what is the receptive field of of a V1 cell made up of?
- single LGN cell: the receptive fields of many retinal ganglion cells
- single V1 cell: receptive fields of many LGN cells
*essentially, info from many sources are processed down into a single target, V1. this is why the V1 is so important.
28
where do neighbouring locations in the retina project to in the visual cortex/occipital lobe?
- they correspond to neighbouring areas in the visual cortex
- receptive fields in retina are arranged in a topographic map in the primary visual cortex
- i.e. areas A and B are beside each other in the retina and also in the right side of the occipital lobe. same w/ areas C and D. except, AB go from below to above and CD go from above to below.
29
how does the brain divide its labor in respect to visual processing?
- divides labour into regions tht perform specific tasks
- even tho neurons can responds to more than 1 attribute of a visual stimulus, they generally respond most strongly to a specific attribute
30
how can we begin to understand the evolution of the eye?
by observing light sensitive organs in animal species
31
how many stages are there to eye evolution?
5
32
what might’ve been the first to use light as energy?
- algae
- created action potentials from light
33
what could eyes have started out as?
- simple light sensitive patches that can detect the presence or absence of light
- i.e. what a leech would have
34
what could have happened to the simple light sensitive patch?
- curved into a slight depression = advantage of sensing direction that the light is coming from
- i.e. what clams have (cup eyes)
35
what could the curved eyes have developed into?
- a pinhole aperture
- helps resolve the detail of an image by changing the amnt of light that enters the eye
- relatively rare
- i.e. abalone/nautilus
36
what did the pinhole aperture develop into?
- crude lens
- spherical shape, has cornea
- relatively solid, shape doesn’t change
- better for organisms that don’t rely heavily on visual acuity
- i.e. fish and scallops
37
wht did the crude lens develop into?
- adjustable lens
- flexible
- can adjust, focus, and process things at varying distances
- found in vertebrates, inc. humans
38
what is evolution an example of?
cumulative selection
39
cumulative selection
evolutionary process whereby new adaptations are layered upon old adaptations
40
what condition must be met for an organ to evolve?
advantages of the modification must outweigh the metabolic cost of growing/maintaining the modification
41
what factors affect the variance in eye structure across species?
- living in an area with lots of light/no light
- does food come from above or below
- movement, colour, and shape of prey
42
two categories of eyes
- simple
- compound
43
simple eyes
- found in vertebrates, like humans
- AND in molluscs such as octopus and squid
- have eyeball, lens, and retina
- including eyes w/ crude and accomodating lenses
44
compound eyes
- found in arthropods, like insects and crabs
- made up of an arrangement of individual tubule units called ommatidium/ometidia
- each ometidia points in a diff direction to gather the light tht is directly in front of it
- form a single image by putting together many separate signals from each ometidium
45
what are compound eyes good at?
detecting movement at close distance
46
what do environmental factors play a role in, w/ respect to the eye?
- shape/orientation of pupil
- size of eye
- where eyes r placed on head
- where most photoreceptors are located on the retina
47
two main functions of the eye
- resolution (acuity)
- sensitivity (ability to get enough light)
48
what size of eyes tend to have better acuity/sensitivity?
- usually larger eyes
- bigger eyes found in species that need better eyesight
49
what allows more light to enter the retina?
- larger pupil size
- greater number of rods in the retina
50
why is there a trade off between large eyes for acuity and large eyes for night vision
- large eyes can either be filled w/ more rods = excellent night vision
OR
- more cones = excellent acuity
- evolution rarely selects for both
51
why do humans and hawks have big eyes?
- excellent acuity
- poor night vision
52
why do cats/horses/owls have big eyes?
- poor acuity
- excellent night vision
53
why do certain deep sea animals have big eyes?
- excellent acuity
- excellent night vision
- bc they need to hunt in the deep sea
54
what does eye placement on head lead to a trade off between?
depth perception and total view of environment
55
laterally-directed eyes
- eyes located on both sides of head (i.e. rabbits)
- large total view
- two separate visual fields = poor depth perception
56
front-facing eyes
- typical for predators, inc. humans
- both eyes directed to front
- narrow total view
- single field of view = excellent depth perception (like binoculars)
- key asset for successful hunting
57
least developed sense at birth
the eye/vision
58
when are eyes formed?
- 2nd prenatal month: eyes are formed
- 6th prenatal month: react to light, some random firing of retinal cells occurs (critical for organized wiring of retinal cells)
59
why is our visual system the least developed sense at birth
- visual stimulation is required for vision to be made fully functional
- not possible when baby isn’t exposed to light
60
eyes in newborns vs. at 3 months
- newborns: weak lens muscles, focusing is limited, pupil can’t react to changes in light
- 3 months: adult-like level of focusing,
61
retinal cells in newborn vs by 11 years
- newborn: low cell density than adult retina, immature cells ESP in fovea
- 11 years: visual brain area development is complete
62
when do retinal cells reach adult-like levels?
4 years
63
when does visual brain development fully complete?
11 years
64
what can a newborn see at 20 feet?
what an adult can see at 600 feet
65
what can a 6 month old see at 20 feet?
what an adult can see at 100 feet
66
wht can a 1 year old see at 20 feet?
- close to adult-like acuity
- fully reach this at 4-6 years
67
what two things happen when we interact with our environment?
- sensory systems gather raw input from the world
- that input is interpreted
68
sensation and perception: what are they and which is simpler?
sensation:
- transforming signals of the world into electrical signals in our nervous system
- this is called signal transduction
perception:
- outcome of the processing of sensation
*sensory processes are simpler than perceptual processing
69
what can pigeons perceive and why?
- infrared light
- because they have 5 cones
70
how much of the world do we perceive?
- we perceive a little bit of the entire world
- only a small fraction of that information gathered by sensory organs makes it to conscious awareness
71
why is it good for information to be filtered out at stages of perceptual processing?
prevents us from getting overwhelmed
72
the inventing brain
- brain fills in gaps bc we don’t perceive everything in the environment
- sometimes the brain misinterprets stimuli (illusions like the necker cube and the two line/arrows)
- however, perceptual systems generally serve us well
73
why is vision the most extensively studied sensory modality?
- most decisions are made using what we can see (navigation, access resources, mates, and danger)
- up to 50% of cortex is used for visual processing
- easier to manipulate visual stimuli than other sensory modalities to learn abt brain
74
how much of the focusing power of the eye does the cornea account for?
80%
75
diff btwn cornea and lens
- cornea is static
- lens is flexible
76
hyperopia vs myopia
hyperopia:
- farsightedness
- can see distant, not near
- light is focused to hypothetical location behind retina
myopia:
- nearsightedness
- can see closer, not far
- light is focused to hypothetical location in front of retina
77
cause of hyperopia
- slightly shorter eye length
- less curved lens
- accommodation process is disrupted
78
causes of myopia
- longer eye length
- more curved lens
- accommodation process is disrupted
79
what can be used to treat myopia and hyperopia?
- corrective lenses
- laser eye surgery
- redirect refractive error problems by redirecting incoming light to its correct location on retina
80
what three cells exist in the second layer of the retina?
- horizontal cells
- amacrine cells
- bipolar cells
81
ratio of rods to cones?
20 rods: 1 cone
82
another word for scotopic
low light
83
rhodopsin
- a photopigment that is sensitive to light
- exists in rods
84
iodopsin
- photopigments tht are less sensitive to light
- exist in cones
85
are cones or rods chromatic?
- cones
- three types of cones sensitive to a diff. wavelength of light
86
convergence
some number of neurons receive input and relay signal to fewer neurons
87
how many rods/cones converge onto one ganglion cell? what does this mean?
- 120 rods onto 1 GC
- 5 cones onto 1 GC
- greater convergence for rods = better vision in the dark BUT poorer acuity
88
what happens when we transition from a bright environment to a dark environment?
1. during first few minutes, there’s a lower threshold for the activation of cones so our sensitivity to light increases rapidly.
2. after 5-10 mins, the threshold of rods decreases significantly whereas cone continues on consistently (at point labelled “rod-cone break” on graph).
- thus, the adaptation to the dark involves two processes that operate at diff. timescales
89
what an bipolar cells do to downstream ganglion cells?
- turn their activity on or off
- thus, other cells in btwn photoreceptors and ganglion cells can modulate the message sent
90
receptive field of ganglion cells
area of retina which affects the firing rate of the ganglion cell when stimulated by light
91
what did kuffler find about the receptive field properties of the ganglion cells?
- stimulating inside receptive field = increased firing rate
- stimulating outside the receptive field = no change in firing rate
- simulating the outer perimeter within the receptive field = opposite response of when centre of receptive field is stimulated
92
what is the structure of a ganglion receptive field?
- circular
- the centre elicits a response when exposed to light, and it has an antagonistic surround which causes an opposite response when exposed to light
93
centre-surround antagonism
- bc the centre and surround of the ganglion receptive field cause opposite responses
- on-center: when light reaching surround = excitation
- off-center: when light reaching centre = excitation
94
when did the first “proto-eyes”/light-sensitive spots emerge?
540 million years ago
95
flat eye
- patch of photoreceptors
- found on jellyfish and other primitive invertebrate
96
binocular zone
where visual fields overlap
97
nasal/temporal hemi-retinas
- nasal: half of a given retina closest to the nose
- temporal: half of a given retina closest to the temporal lobe
98
what do the nasal and temporal retinas in the right eye see? why?
- nasal retina sees right side of world
- temporal retina sees left side of world
- bc. the lens flips the image
99
which retinas see the same areas of the same environment?
- right nasal retina and left temporal retina
- left nasal retina and right temporal retina
100
what part of the brain controls pupillary reflexes in response to changes in brightness?
pretectal area of midbrain
101
what regulates circadian rhythms?
retinohypothalamic fibers
102
what controls saccadic (high velocity) eye movements and coordinates visual/auditory/somatosensory information?
superior colliculus
103
what does our ability to localize the source of a sound rely on? i.e. eyes r closed, and someone snaps their fingers, we know where it came from
- translate auditory localization into a neural representation of space
- done by places like the superior colliculus which align auditory and visual maps together
104
how many subcortical targets does the optic tract project to?
- four
- pretectal area of midbrain
- retinohypothalamic fibre
- superior colliculus
- LGN
105
how many retinal inputs terminate at the LGN?
90%
106
does the LGN only get information from the retina?
- no
- also from brain stem, thalamus, and higher-order centres
- it integrates this info
107
how many layers of cells does the LGN have? what does each layer get info from?
- six layers
- each layer receives input from ONE eye and ONE of two distinct retinal ganglion cell types
- layers 1 and 2 get info from M-cells
- layers 3/4/5/6 get info from P-cells
108
ganglion cell types
P-cells:
- parvocellular cells
- smaller cell bodies
- convey info tht helps w/ colour perception, pattern, form, texture, and depth
M-cells
- magnocellular cells
- larger cell bodies
- convey info abt movement
109
what kinds of receptive field properties does the LGN have?
- similar as the retina
- slightly larger
- as such, a single LGN cell corresponds to a sliiightly larger area of visual space
110
what is area V1 made up of?
- sheet of grey matter abt 2mm thick
- has six layers of cells
- 52 distinct regions exist in the layers of V1
- areas 17,18, and 19 play large role in visual processing
111
line of gennari
- a long stripe in the cortex
- also corresponds to layer 4 of V1 (principle layer for input from the LGN)
112
are all areas of the visual field equally represented in V1?
- no
- the degrees closest to the centre of the visual field (which is mapped onto fovea) is overrepresented in the V1
- a small area of visual field has the largest area in V1 = most processing
113
types of V1 neurons
simple cells:
- respond to vertical bar of light but not when it was turned
- others respond to specifically to bars of light that are at specific angles
complex cells:
- sensitive to orientation AND direction of lights movement
hypercomplex cells:
- sensitive to orientation, direction, AND length of light
114
what did huble and wiesel call V1 cells? why?
- feature detectors
- because they respond specifically to discrete features (orientation/size/movement)
115
columnar layout of V1
cells above/below each other tend to share similar properties
116
ocular dominance columns
- in layer 4 of V1, inputs from the two eyes are relatively separate
- all cells in one column respond to input from one eye. all cells in neighbouring column respond to input from the other eye
117
how are simple cells in V1 grouped?
- orientation columns
- same orientation preferences are grouped together within columns
(bc simple cells respond to orientation)
118
primate extrastriate cortex
- has areas V1, V2, V3, V4, V5/MT and IT
- V2/V4/IT are the “what” pathways
- V3/V5 are the “where” pathways
119
monocular depth cues
- used to estimate distance w/ info rom just one eye
- broken down into three categories: accommodation, motion-based, and pictorial clues
120
explain the three categories of monocular depth cues: accommodation, motion, and pictorial cues
accommodation:
- change in tension of muscles surrounding lens also serves as a depth cue
motion:
- motion parallax: diffs in perceived speed of nearby and distant objects
- optic flow: perceived motion in visual field that results from one’s own movement
pictorial:
- interposition: when one object overlaps another object
- linear perspective: parallel lines appear to converge on a single vanishing point in the horizon (one-point perspective)
121
two other depth cues
- aerial perspective
- shading
122
aerial perspective
- objects in the distance appear hazy/bluer bc of the atmosphere’s impact
- leonardo da vinci discovered this
123
shading
- we expect light to come from above us
- we use this to assume how shadows should be cast
- helps us infer direction of light
124
stereoscope + how it works
- a device that creates the illusion of depth from a 2D image
- he realized our depth perception exists bc our two eyes capture same scene from two slightly diff angles
- he took two photographs of the same scene 60mm horizontally from each other
- when both items were presented simultaneously, the scene was perceived as having depth
125
the overall ability to perceive depth suing binocular disparity is called…
stereopsis
126
what happens as objects move closer to our face?
- extraocular muscles move (muscles around the eye) as the gazes of both eyes converge
- this is another binocular depth clue
- this is called “convergence”
127
how does depth perception present at various ages?
4 months:
- reaching preference for nearer objects
6 months:
- discern deep/shallow to avoid dangerous heights
128
is depth perception innate or learned?
- mixture of both
- monocular depth perception (using cues like texture/overlapping objects) must be learned
- some basic depth capabilities exist at birth
129
what are the two binocular depth cues?
- stereopsis
- convergence
130
at what age do infants start using depth cues?
abt 6 months
131
ROYGBIV
- the elementary components of the colour spectrum
- thus, they can not be further divided
132
what if a light is v impure and has many different wavelengths?
looks grey
133
how many distinguishable steps of saturation exist for each hue?
20
134
how many steps of brightness are we sensitive to?
500
135
how many colour variations can our visual system distinguish between?
over two million
200 hues x 20 saturations x 500 brightnesses
136
how many hues can we discriminate between?
200
137
types of colour blindness
- protanopia: loss of red cone
- deuteranopia: loss of green cone
- tritanopia: loss of blue cone
138
8% of males and less than 0.5% of females have red-green colour blindness. why?
- gene that causes red-green colour blindness is on the X chromosome
- in females, chromosome w/ intact gene takes dominance = normal vision
- son of a woman carrying a fault gene has a 50% chance of inheriting the faulty X chromosome
139
preferential look paradigm. used to test infants. presented with grey card and plan grey striped card. wht happens?
- good acuity: will look at striped card
- bad acuity: will have no preference bc both cards will seem grey
140
EEG methods are the hold standard for measuring visual abilities. why aren’t they often used for infants?
- time-consuming
- functions best when infants sit still
- requires 1000s of trials
141
when can infants distinguish between opposing colours (i.e. green and red) and prefer moving objects?
2-3 weeks
142
at what age can children mentally “connect the dots” of separated dots of light of biological motion to see larger configurations?
3-5 years
143
what do slit-shaped pupils do better?
- enhance visual acuity
- increases range of intensities at which the eye can function effectively
- prevents chromatic aberration: when wavelength of light enters the periphery and blurs the resulting retinal image
144
what do round-shaped pupils do better than slits?
- night vision
- allow more light to enter pupil
145
why can golden eagles see so well?
- larger/flatter retina
- 1 million cones per millimeter of fovea
- have a second fovea in retina
psych 1xx3
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