Module 3: Sensation and perception Flashcards
1
Q
what is one characteristic of sensory aftereffects?
A
The aftereffects happen in the opposite direction relatively to the adaptor (initial sensation)
2
Q
what are aftereffects due to?
A
Due to Troxler’s fading and sensory adaptation
3
Q
explain in detail what happens during aftereffects.
Explain Troxler’s fading.
A
During after effects, the brain adapts to the sensory input it is receiving, and becomes less responsive to them and more responsive to new inputs. (new inputs become more salient)
Troxler’s fading is when the old input fades and the new input seems stronger (brighter)
we are more responsive to it
4
Q
are we aware of Troxler’s fading when it happens?
A
No. this phenomena happens slowly and we do not realize that this sensory adaptation is happening when it is.
5
Q
is adaptation only visual?
A
no. it happens in all sensory modalities.
6
Q
is sensory adaptation in other modalities the same as in the visual one? how so?
A
yes, the same things are experienced.
1) opposite experience to the adaptor
2) higher salience of new inputs
7
Q
how is sensory adaption useful in daily life?
A
it helps keep us alert of any new stimuli.
8
Q
what do perceptual aftereffects tell us about our brain?
A
it tells us that we do not have a veridical impression of what happens around us in the world, and that our experiences are the product of activity patterns in our brain.
perception is useful but not accurate.
8
Q
what do perceptual aftereffects tell us about our brain?
A
perception is useful but not accurate.
it tells us that we do not have a veridical impression of what happens around us in the world, and that our experiences are the product of activity patterns in our brain.
9
Q
give an example of auditory adaptation.
A
McGurk Effect
it’s when we hear different things when the sound is accompanied by lip movement.
10
Q
what does the McGurk effect tell us?
A
we do not have the veridical impression of inputs from single sensory modalities. Our brain averages the inputs (averaging sound and vision of lips movement) and gives us different information than we would experience had those inputs been experienced in isolation
11
Q
what are sensory organs good for if our experience of the wold is based on brain activity only?
A
sensory organs take the external signals and TRANSDUCE them into electrical signals that can be relayed to the brain for processing
12
Q
what is the nature of the signals sent to the brain?
A
electrochemical
13
Q
what is the first step of perception?
A
transduction of external signals in the sensory organs.
14
Q
what are the 2 most important sensations for humans?
A
vision and audition
15
Q
what is sound?
A
sound is a wave that changes the pressure in the air until it reaches our ear by exerting a force on the air molecules. Once in the ear, the hair cells found in the cochlea transduce these waves into electrochemical signals sent to the brain
16
Q
what are the 2 characteristics of a sound wave? and what does each of them tell us about the sound?
A
amplitude and frequency
- amplitude: related to the intensity of the sound (high amplitude = high intensity = loud noise) (low amplitude = low intensity = quiet noise)
- frequency: how much the waves fluctuate the pressure of the air molecules in a certain time frame.
related to the pitch of the sound.
rapid fluctuations = high frequency = high pitch (aigu)
slow fluctuations = low frequency = low pitch (grave)
17
Q
how are the wavelength and the frequency of sound waves related?
A
inversely
long-wavelength = low frequency
short-wavelength = high frequency
18
Q
what are hair cells and where are they located?
A
hair cells have hair-like structures.
they are found in the cochlea and are surrounded by the ear liquid. they bend back and forth when the sound wave makes the liquid vibrate.
19
Q
describe the process of sound wave transduction in the cochlea.
A
1- the sound wave makes the liquid vibrate
2- the hair cells bend
3- ions rush to the top of the hair cells
4- hair cells release chemicals at the base
5- those chemicals bind to the auditory nerve cells
6- the auditory nerve cells create a signal that propagates the signal from the nerve to the brain.
20
Q
what is the primary sensory modality in humans? provide proportions.
A
vision
30% of our cortex for vision
3% of our cortex for audition
21
Q
in the eyes, what is the main element involved in transducing signals into electrical signals sent to the brain?
A
photoreceptors.
22
Q
where are photoreceptors located?
A
in the retina
23
Q
what is the unique element of photoreceptors? why is it special?
A
the pigments (found in the photoreceptors0
they are the ones who absorb the photons of light
24
describe visual transduction.
1- the light hits the eyes.
2- in the retina, the photoreceptors absorb the photons of light.
3- a wave of depolarization occurs
4- the conductance of the photoreceptors' cell membrane changes.
5- Ganglion cells receive the signals from the back of the photoreceptors and coverage into the optoc nerve
6- the optic nerve sends the electrochemical signal to the brrain
25
where exactly are the pigments located?
in the back of the retina, away from the light source
26
why is the human eye considered rubbish as an optical instrument?
because the light has to go through several layers (which refract light) before reaching the photoreceptors and the pigments, the image arrives blurred
27
what is the blind spot?
it;s the spot where the optic nerve leaves the retina. there are no photoreceptors there and if an image falls in that area, it is not seen.
28
are humans aware of their blind spot?
no. but they can demonstrate it
29
what are 2 phenomena that prove that we do not have veridical impressions of what reaches our eyes, and that the brain predicts things based on available evidence?
1- Perceptual filling in when something goes through our blind spot, we don't see a hole in it. our brain infers what should be there and shows us that sensation.
2- Neon color spreading: we see the background color different than what it really is due to surrounding colors.
30
what can we characterise our visual system as?
a detective agency
it puts together hypotheses of what could be based on available evidence
31
what is naive realism?
it's the common mistake of believing that our perception of the world is exactly what it is.
32
what are the 2 types of photoreceptors in the retina? which one is responsible for detecting color?
cones are rods.
cones detect color, rods detect shapes (edges, etc...)
33
what is the color of light dependent on?
the wavelength
34
what is the wavelength range perceived by the human eye?
400 nm (blue) to 700 nm (red)
35
there are 3 types of cones.
what are they and what wavelengths do they absorb?
short cones: 430 nm
medium cones: 530 nm
long cones: 570 nm
36
based on what cones are activated, we perceive different colors. there are 3 special cases, what are they?
WHITE: all cones are maximally activated.
BLACK: all cones are minimally activated.
GREY: all 3 cones are equally activates.
37
what is the basis of color vision?
describe it in the extremities of the wavelength range in humans.
basis of color vision = activation of the different cones.
blue light: maximally activates short cones, minimally activate medium cones, does NOT activate long cones AT ALL.
red light: maximally activates long cones, minimally activate medium cones, does NOT activate short cones AT ALL.
38
humans are trichromats. what does this mean?
give examples of other ---chromats.
trichromats have 3 classes of cones.
birds have 4th class: they can see ultraviolet light. (tetrachromats)
dogs are dichromats, they have 2 classes of cones. (blue and yellow)
39
what humans are more prone to color blindness? what is it? what is it due to?
1% of males don't have long cones
1% of humans don't have medium cones
it's important to have the 3 types to distinguish between red and green, and so these males have red-green color blindness.
they have a vision similar to dogs and cats.
40
why is red-green color blindness less prevalent in females?
the defective genes is on the X chromosomes.
41
some males are dichromats like dogs.
however, some females have a 4th class of cones. What does that provide them with?
Superhuman color vision
they can distinguish between more colors than us. they are tetrachromats like birds.
42
are people with color vision deficiencies aware of that? why?
no. because as children, we learn colors by associations, so we learn the wrong associations without knowing they're wrong
42
are people with color vision deficiencies aware of that? why?
no. because as children, we learn colors by associations, so we learn the wrong associations without knowing they're wrong
43
do all trichromats with normal color vision see the same?
no. because each person has different ratios of the different cones (photoreceptors)
44
is the ability to distinguish between different wavelengths only based on the cones?
no
it is also reliant on the structure of the retina
45
what is the goal of vision with regards to illumination?
to discard its effect
46
what color is artificial lightning? and natural lighting?
artificial = blue
natural = yellow
47
when we're inside (artificial lightning), a human face will refract more blue light then when we're outside. What process prevents us from seeing a blue face?
Color constancy
48
what is color constancy?
process by which the visual system will substract the effect of lightning and allow us to see colors for what they are.
49
what color will the visual system subtract?
The brain will subtract the wavelength of the prevailing light source
it will subtract the color of the lightning
for example: if an object is lit by natural sunlight, our visual system will substract yellow
if lit by artificial light, visual system subtracts blue
50
describe the primary visual pathway
1- eyes
2- optic nerve
3- optic chiasm
4- lateral geniculate nuclei (subcortical structure)
5- primary visual cortex (V1) in the occipital lobe
51
what happens at the optic chiasm?
it's where the information splits:
from left visual field to right hemisphere and vice versa
52
how do we know if the problem is due to the brain or to the eyes?
if the problem is specific to INFORMATION : eyes and optic nerve BEFORE THE CHIASM
if problem specific to one side of the visual field: brain damage
53
is V1 the only region to receive visual input?
no.
it's the FIRST cortical region in the brain to receive visual input
54
how are the responses in V1 mapped out?
retinotopically
55
what does retinotopic mapping mean?
give examples.
adjacent neurons in V1 will respond to inputs in adjacent positions in the retina.
- neurons at the top of V1 respond to input at the bottom of the visual field.
- neurons at the bottom of V1 respond to input at the top of the visual field.
- neurons at the anterior part of V1 respond to input at the peripheries of the visual field. (the more peripheral, the more anterior)
- inputs at fixation project on the fovea (front of the eyes). Response from neurons at the BACK of V1
56
Which visual brain regions have retinotopic mapping?
ALL of them
57
what is cortical scotoma and what are the consequences?
it's when regions of V1 are damaged
V1 takes inputs from ALL the visual field. If we are blind to some area of the visual field = the region in V1 that codes for that area is damaged
58
what phenomena proves that the brain (V1) sees things that we cannot see? (are unaware of)
flicker fusion threshold for color
59
describe flicker fusion threshold for color and how it works.
when a light of certain color is flickering, the flickering have a frequency to which we can single out each color.
at 30 Hz, we cannot differentiate between the 2 colors anymore, and we see a constant color (the average of the 2 colors: yellow average of red and green)
HOWEVER, in V1, cells are still responsive to both the colors, we just can't see them
60
what is V1 necessary for? is it the only visual pathway?
V1 is necessary for conscious/aware vision.
It is NOT the only pathway, there are 2-3 other pathways.
61
what is blindsight due to ?
damage to V1
62
what do we use to quantify the extent of the damages done to V1?
perimetry
63
the 2 cases of cortical damage are partial and complete. describe what happens in each case.
partial damage: blind to inputs from a certain side of the field of vision (coded by the damaged V1 region)
complete damage: blind to ALL the inputs from the certain side of field of vision (coded by the damaged V1 region)
64
discuss the process of perimetry
when patients fixate a point and we flash inputs to either sides of that fixation point (various areas of the field of vision) , then we ask the patient whether they saw that or not
65
what is a modification made to perimetry? and what do we call that new technique?
the two-alternatives forced-choice task
instead of asking the patient whether they saw the flash or not, we restrict their answer: "was the flash to the left or to the right? was it red or greed?"
66
what does blindsight tell us about human vision and V1? how is this demonstrated?
It shows that V1 is necessary for conscious and aware vision, but we can carry out some visual activities without V1 through other visual pathways.
for example, we can avoid obstacles -> Helen the monkey and TN
67
what is signal detection theory and why was it established?
check notes
to measure sensitivity in cases of uncertainty.
it was established because patient subjectivity to the presence or absence of a stimulus is not enough to measure sensitivity to that stimulus.
68
what are the 4 categories of responses in a signal detection theory?
explain what each of them mean.
hit, miss, false alarm, correct rejection.
hit: report the signal is present when it actually is.
miss: report the signal is absent when it's present.
false alarm: report the signal is present when it's not.
correct rejection: report the signal is absent when it really is.
69
what 2 categories are evaluated in a signal detection theory?
what do we calculate with them? what does it stand for?
we evaluate the hits and the false alarms
we calculate d' (d prime)
d' = ration of hits to false alarms
d' = hit / false alarm
70
when d' = 0, it is represented by a horizontal line passing through the origin.
What does this mean in terms of signal sensitivity?
when d'=0, it means that the participant reports the signal being present equally as many times when it's present and when it's absent. (hits = false alarms) (ratio = 1)
71
When people ALWAYS report seeing the signal even if it's absent, what does that mean?
it means that there is an equal hit and false alarm rate of 1
72
When people NEVER report seeing the signal even if it's present, what does that mean?
it means that there is an equal hit and false alarm rate of 0
73
what is a patient reporting when the hit and false alarm rates are equal, and equal to 0.5?
it means that the patient is guessing, and the signal is reported to be present on half of the trials, even if it wasn't
74
How can we, using those rates, suggest if a person has any sensitivity to the signal?
In what area of the graph is this visible?
if the hit rate is well above the false alarm rate
it is seen in the area of the graph ABOVE the horizontal line of d'=0
75
what did researchers find through the signal detection experiments?
they found that people had visual sensitivity even when they insisted that they couldn't see
76
in times of uncertainty, what are human fingerprint experts biased to reporting?
they report that the fingerprint doesnt match the crime scene.
this is a miss when it actually matches.
77
describe another every day situation where this signal detection theory is implemented.
airpot security. They are so used to never finding threat in the baggage, but this assumption that all people are abiding is dangerous, because it can cause misses. (reporting no threat when there actually is a threat)
78
besides sensitivity, hat does the signal detection theory detect?
bias
79
what are the selective visual deficits?
color and motion
i can't see color nor motion but i can see everything else
80
what do all visual neurons in the brain possess?
a receptive field and response selectivity
81
what is receptive field?
it's the region on the retina onto which the signal should fall on so that the neuron responds to it
82
what is the response selectivity in neurons?
each neuron will respond to a different type of input : color, motion, motion direction.
83
what do cortical cells respond to ?
they do NOT respond to spots of light.
they respond to complex inputs like oriented inputs (oriented lightning)
84
what do visual cells, cells of the LGN and sub-cortical cells respond to?
spots of light
85
which visual cells respond to spots of light?
visual cells, cells of the LGN and sub-cortical cells
86
how is the structure of human vision characterized as?
a processing hierarchy
87
explain the concept of processing hierarchy in human vision.
thefirst region to receive inputs is V1.
V1 responds to simple things. (bars of light with specific color, specific motion direction, etc...)
V1 projects the signal to other cortical cells
those cells respond to more complex inputs
The cortical cells respond to specific faces, specific types of objects, specific motion or object orientations, etc...
-> all these complex selectivities are formed by taking inputs from cells at a lower processing stage (V1 initially)
88
what are the other 2 brain regions we are interested in (besides V1)
V5 and V4
89
what do cells in V5 respond to?
they respond to complex patterns of motion (direction tuned cells)
90
do cells in V5 respond to color?
No
None of the cells in V5 respond to color
91
do complex motion and flickering activities ONLY activate V5?
no. They activate V1
V1 responds to ALL visual inputs, but due to the processing hierarchy, it sends more complex inuts to higher processing cortical cells
92
what do V4 respond to ?
Mostly to color.
few of V4 cells respond to direction of motion
93
how do we locate the response selective cells?
using fMRI
94
Which cortical regions respond to faces?
the Occipital Face Area (OFA)
the Fusiform Face Area (FFA)
and the Superior Temporal Sulcus (STS)
94
Which cortical regions respond to faces?
the Occipital Face Area (OFA)
the Fusiform Face Area (FFA)
and the Superior Temporal Sulcus (STS)
95
where are the cortical regions tuned to face recognition located in the brain?
in the temporal lobe (on the side of the brain)
96
what deficiency is caused by daage to the V4 regions?
Achromatopsia (complete or partial)
97
what happens in the case of complete achromatopsia?
normal vision but NO color vision at all
98
what happens in the case of partial achromatopsia?
depending on the hemisphere where the damage is, color from the adjacent side of the field of vision is not reported.
(left V4 damaged, color from right side of vision lost)
99
what do we call the condition where the regions in both the brain hemispheres are damaged?
BILATERAL damage
99
what do we call the condition where the regions in both the brain hemispheres are damaged?
BILATERAL damage
100
if OFA is damaged, what results?
Prosopagonia
the inability to recognize faces. We recognize it's a face, but we don't know WHO it is. (rare and extreme case: wife's face is mistaken for a hat)
100
if OFA is damaged, what results?
Prosopagonia
the inability to recognize faces. We recognize it's a face, but we don't know WHO it is. (rare and extreme case: wife's face is mistaken for a hat)
101
what is motion blindness?
cerebral akinetopsia
102
what is cerebral akinetopsia?
motion blindness.
103
can cerebral akinetopsia be partial?
no it can only be complete.
it is very rare and very dangerous for every day life
104
What region is damaged for cerebral akineotpsia to happen?
V5
105
if only one V5 region is damaged, can cerebral akineotopsia develop?
NO. either both are damaged or no disease.
this is why it's so rare
106
What is the binding problem?
the brain has to combine activity from different brain regions to generate a coherent perception. This process is error prone and the wrong signals can be binded. This is the binding problem
107
what is brain functional modularity?
when different regions in the brain process different inputs
108
what is the most commonly knwn Mis-binding?
mis-binding color and motion
109
what is the basis of mis-binding?
the brain assumes that what prevails in central vision is also true in the peripheries.
110
what is V5 highly involved in?
planning movements and processing motion
111
what is associative agnosia?
when a person cannot verbally report orientations but can
112
what is comorbidity?
when having one deficit leads to another deficit.
113
where is the OFA usually located?
in the right hemisphere, adjacent to V1 and V4 (leads to comorbity in deficiencies)
113
where is the OFA usually located?
in the right hemisphere, adjacent to V1 and V4 (leads to comorbity in deficiencies)
114
what are the 2 kinds of the binding problem?
temporal and spatial
115
whhy can we say that we are living in the past?
because the visual cells only respond to stimulus after they are received ( 30ms to 104 ms)
116
cerebral akinetopsia can be a transet phase. What does that mean?
that it can predict things (migraine for ex)
117
from fastest to slowest, which cells respond to visual stimulus?
LGN cells -> after 30 ms
V1 cells -> after 66 ms (50%)
V5 cells -> after 72 ms
V4 cells (the slowest and sluggiest) -> after 104 cells
118
what is color/motion asynchrony?
when the wrong motion direction and color are binded
118
what is color/motion asynchrony?
when the wrong motion direction and color are binded
118
what is color/motion asynchrony?
when the wrong motion direction and color are binded
119
does the binding problem resolve? how?
yes
but we don't know HOW (Research ongoing)
