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PSYC 102 - sensory > Perception > Flashcards

Perception Flashcards

1
Q

what is sensation

A

the process of transforming physical stimuli to electrical (neuronal) signals

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2
Q

what is transduction

A

turning one signal into another

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3
Q

what is perception

A

the process of interpreting these signals for conscious awareness or for action

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4
Q

explain retinal implant

A

for macual degeneration / retinitis pigmentosa
silicone microelectrode array implanted in damaged retina
sends electrical signals directly into the cells that carry info to the brain

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5
Q

explain neural prosthesis

A

treatment of quadriplegia

96 electrodes implanted into motor cortex = can think about moving and machine will then move

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6
Q

why do we study vision so heavily

A

its what we know the most about

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7
Q

explain the major theme of perception

A

it is an inference
your brain is doing its best to figure out whats going on given the limited input
percetion is ongoing and more than just a passive sensation
perception is rarely ambiguous - the brain jumps to conclusions, or tries to force an interpretation on a scene (eg the necker cube - we see one or the other, never both simulataneously)

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8
Q

how do we see (ideas not specific)

A

with our brain not our eyes

often the interpretation imposed by the brain is based on prior experience on what is most likely

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9
Q

what part of the electromagnetic spectrum do we see

A

the visible spectrum

400nm to 700 nm in waelenght (blue to red)

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10
Q

explain the four receptors in the retina

A 
blue cones - absorb blue light
rods
green cones - absorb green light
red cones - absorb red light
cones support colour vision
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11
Q

whats special about matis shrimp

A

12 photoreceptors
but they are rubbish at colour vision
shrimp brain cant process it all
we are much better at seeing with our brains

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12
Q

vision (and perception in general) is always…..

A

constructive and filtered through your own experience

perception is always dependent on a combination f bottom-up sensory information and top-down knowledge

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13
Q

why do we study perception

A

think about natural vs aritificial images
our ultimate goal is to undersatnd the visual system - go from light to perception in a step by step process
this is tough so instead we take a reductionist approach - how does the brain understand the smaller pieces

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14
Q

natural image vs artifical stimuli

A

natural - what we actually see

artificial - what we use in the lab

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15
Q

why do we use artificial stimuli in the lab

A

we can ask much more systematci questions

for example whats the smallest change in orinetation of lines we can perceive

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16
Q

what is threshold and what does it tell us

A

threshold is the smallest change the observer notices
is tells us how sensitive the observer is to a particular feature
these thresholds inform us about perceptual capabilities
eg colour code different bits of brain cells to different types of stimuli

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17
Q

how to study perception (3 ways and goal)

A

1 behavioural measurements - psychophysics
2 physiological and behavioural measurements in animals
3 physiological and behavioural measurements in humans
goal - link neural activity with perception and behaviour

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18
Q

what is psychophysics

A

performing behavioural measurements to determine how well stimuli are perceived

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19
Q

go through magnitude estimation psychophysics example

A

stimuli are above the threshold
observer is given a standard stimulus and a value for its intensity
observer compares the standard stimulus to test stimuli by assigning numbers relative to the standard
response expansion - as intensty increases, the perceived magnitude increases more quikcly than the stimulus intensity eg shock
response compression - as intensity increases the perceived magnitude increases more slowly than the intensity eg brightness

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20
Q

explain the two types of threshold estimation

A

absolute threshold - the minimum intensity of stimulation required to produce a detectable sensory experience 50% of the time - detection
difference threshold - the minimum chnage in intensity required to produce a detectable change in sensory experience about 80% of the time (this is also known as the just noticeable difference) - discrimination

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21
Q

explain graphs for creating a psychometric function for absolute threshold by method of constant stimuli

A

plot 6 values of light intensity against percentage stimuli detected
now can find the 50% threshold point where the light at that intensity would be detected 50% of the time through interpolation

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22
Q

explain frequency vs pitch in auditory perception

A

the psychological experinece of pitch is related to the temporal frequency of vibrations of air hitting the eardrum
so double the frequency = double the octave of the pitch

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23
Q

how to measure someones JND between two auditory pitches

A

lets use method of constant stimuli
pick baseline value
pick a set of increments
sequentially present baseline and baseline +increment
randomly chose which one comes first and ask subject for the higher frequency (chance = 50%)
plot the psychometric function
the difference threshold is the value that gives 80% correct (80% here is just a typicla value)

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24
Q

what is the weber fraction

A

the fractional increase above a baseline value that can be reliably detected
it is the ration difference threshold over the baseline value

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25
Q

what is weber’s law

A

detectable change n a stimulus varies as a function of baseline stimulus value
-constant ration (difference threshol / baseline value)

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26
Q

how did Fulton 1928 study walters brain

A

listened with a stethescope to walter’s buldge on the back of his head
heard nothing when eyes closed
but lots when reading a newspaper

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27
Q

how does fMRI work

A

takes advantage of hemodynamic (blood flow, blood oxygenation)
magnetic properties of blood to indirectly track neural activity
blood oxygenation level dependent (BOLD) signals - oxygenated and deoxygenated hemoglobin have different magnetic properties and so the change in relative concentration can be measuredusing MRI

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28
Q

uses of functional meuroimaging

A 
functional brain mapping
relative neural activity behabiour 
-intact humans
-patients with brain damage
presurgical planning - eg epilepsy or tumour resection
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29
Q

problem with fMRI

A

no temporal resolution - spike appears around 6 seconds after stimulation
but its really safe in humans

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30
Q

when do we use single unit recording and what does it measure

A

as usually surgical normally in non-humans
occasionally used in humans for presurgical mapping
measures firing in one neuron

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31
Q

evaluation of single unit recording

A

perfect temporal and spatial resolution but is only one sample at a time. would have to do it LOADS to be useful

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32
Q

explain multi–unit recording

A

utah ray
rests ontop of the cortical surface
several hundred neurons can be measured at a time

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33
Q

basic overview of neural connectivity

A

pyramidal neuron embedded in a network of neurons
single neurons are connected to over a thousand other neurons
so a single unit activity is reliant on thousands of other neurons

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34
Q

what does the ….. do

cell body

A

widest part of the neuronal body, contains the nucleus and other basic machinery common to most cells

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35
Q

what does the ….. do

dendrites

A

thin branches extending from the cell bisy that recieve signals from other neurons (INPUT)

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36
Q

what does the ….. do

axon

A

a thin tube extending from the cell body that carries electrical impulses away frm the cell body to other cells (OUTPUT)

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37
Q

what does the ….. do

myelin sheath

A

an insulating coating that surrounds some axons that can speed the transition of neural impulses down the axon by attenuating leakeage of current

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38
Q

what does the ….. do

axon terminal

A

the end of the axon, where neurotransmitters are released to communicate with other cells

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39
Q

what does the ….. do

synapse

A

the space between the axon terminal and another neuron’s dendrite or cell body

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40
Q

how does a neuron send a signal to another neuron and explain

A

action potentials - electrical impulses that travel down the axon and influence the activity of the receiving neuron
cause release of neurotransmitters to cross the synapse and bind with receptor sites on the dendrites of post-synaptic cell

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41
Q

roughly how big are synapses

A

20nm

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42
Q

define neurotransmitters

A

chemicals that are released from the axon terminla that cause changes in the electrical potential of the receiving neuron

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43
Q

describe the chemistry at rest of a neuron

A

at rest there is a higher concentration of sodium iond outside and potassium ions inside the cell
net charge is about -70mV (milivolt)
the sodium-potassium pump helps maintain negative resting poential. so 2 potassium go in and 3 sodium must go out

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44
Q

what happens to a neuron when there is an excitatory input from another neuron
explain the whole process

A

the permeability of the cell membrane changes allowing sodium to rush in
the influx of positively charged sodium increases the potential inside the post-synaptic cell (voltage)
when the potential gets positive enough to reach a critical value (about -55mV) it triggers a rapid increase in voltage = action potential
potassium then rushes out to return the neuron to its resting potential
synaptic vesicles release neurotransmitters into the synapse that influence the permeability of the next neuron

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45
Q

what does the myelin sheath make possible and why

A

quick transmission of action potentials - 0.3m/s to 120m/s depending on the size
myelin sheath = a combination of lipids and proteins that covers or insulates many axons (supported by glial cells, primary oligodendrocytes in the CNS)
is white matter
if myelin is systematically destroyed or does not develop properly then serious consequences - multiple sclerosis

46
Q

four important general observations about action potentials

A

they are all or nothing (ie dont get a little action potential)
there is a refractory period after an action potential during which another action potential cannot occur
there is a spontaneous background level of firing in the absence of stimulation
their firing rates vary both with the magnitude of stimulation but also the intensity of external stimuli

47
Q

neurotransmitters are……

A

released by the presynaptic neuron from the vesicles
received by the postsynaptic neuron on receptor sites
natched like a key to a lock into specific receptor sites
used as trigers for voltage change in the postsynatic neuron

48
Q

what do excitatory transmitters do and give an example

A

cause depolarisation
post synaptic neuron becomes more positive
increases the likelihood of an aciton potential
glutamate

49
Q

what do inhibitory transmitters do and give an example

A

cause hyperpolarization
post-synatpic neuron becomes more negative
decreases the lieklihood of an action potential
GABA

50
Q

why is excitatory and inhibitory neurotransmitters important

A

it makes it possible to create neural circuits that can detect very specialised patterns of external stimulation

51
Q

explain spatial summation

A

when multiple neurons simultaneously stimulate dendrites on the same neuron. under these conditions the effects of the stimulating neuron will add togteher in a process called spatial summation

52
Q

explain temporal summation

A

when signlas arrive at the dendrite close together in time, then the effect of the individual signals can add together in aprocess called temporal summation. if the signals arrive too far apart in time then the effect of the first signal will have decayed before the next signal arrives

53
Q

what is the parietal lobe responsible in senses

A

skin senses

54
Q

what is the temporal lobe responsible in senses

A

hearing

55
Q

what is the occipital lobe responsible in senses

A

vision

56
Q

what are cones specialised for

A

daulighy colour vision, good detail

57
Q

what are rods specialised for

A

night grayscale vision, poor detail

58
Q

what is the principle underlying why there are different parts of the visual system

A

principle of modularity or functional specialization

59
Q

gamma waves have….. wavelength whereas radio waves have….

A

gamma - short

radio - long

60
Q

which colour has shorter wavelengths? blue or red

A

short - blue

long - red

61
Q

frequency =

A

speed/wavelength

62
Q

what is the speed of light

A

299 792 458 m/s

63
Q

what does the cornea do

A

focus light onto retina

64
Q

what does the cillary body do

A

ring of muscles around the lens (stretches and widens the lense)

65
Q

explain how light get transduced and sent to the brain and what cells are involved in the right order (and how they are organised)

A

light filters down to rods and cones (they are last)
rods and cones then send signals vertically up through the bipolar cells
ganglion cells
ganglion axons - which form optic nerve

66
Q

what lateral connections are provided in the visual system

A 
horizontal cells (linked to photoreceptors)
amacrine cells (linked to bi-polar / ganglion cells)
67
Q

do we see with photoreceptors

A

no - they transduce

we dont even have access to the signals they produce, its the ganglion cells which talk to the brain

68
Q

whats special about the fovea

A

fovea - pit

has ganglion and bipolar cells peeled away to provide direct light access to the cones

69
Q

where in the eye are there no photorecptors and why

A

the blindspot

this is the area where the optic nerve leaves the eye

70
Q

what is special about octups, squid and terrestrial gastropods etes

A

they have photoreceptors on the “correct” side of the retina. they have no blind spot

71
Q

how is the retina organized and so what is the receptive field

A

retina is organized as a map of external space

the receptive field = area of retina that affects firing of a given neuron in a circuit

72
Q

how do we measure receptive fields

A

by monitoring single cell responses

stimulus is presented to retina and respons of cell is measured using an electrode

73
Q

explain Hubel and Wiesel’s experiment

A

recording on an on centered cell in a cat

they found the refractive field = a small excitatory centre (inner circle) with an inhibitory surround

74
Q

what can we measure to understand what signals are being sent to the brain

A

photoreceptors are connected to long opic nerves
we can record from the optic nerve to figure out their receptive fields and to understand what signals are being sent back to the brain

75
Q

explain how an excitatory center, inhibitory surround works

A

light targetting centre = more action potentials fired

if inhibtory surround is also fully stimulated then decrease in action potentials fired

76
Q

explain the seven-receptor neural circuit underlying a centre- surround receptive field

A

the circuit will encode contrast (differences) - not the absolute intensity of the stimulus
the output of the cell will be the ration of the excitaory to inhibitory cells

77
Q

What is Macular degeneration

A

fovea and small surounding area are destroyed
creates another blind spot on the retina
most common in older individuals

78
Q

what is retinitis pigmentosa

A 
genetic disease
rods are destroyed first
foveal cones can also be attacked
sever cases result in complete blindness
tunnel vision at first
79
Q

what is Glaucoma

A

caused by elevated pressure in the eye
the pressure rises beacuse the anterior chamber of the eye cannot exchane fluid properly
cuts off blood vessels at the optic nerve head, starving the ganglion cells

80
Q

what parts of the eye focus light on the retina and to waht extent

A

cornea - 80%

lens - 20%

81
Q

if the light source is far away the focal point is ……

A

closer to the lens

82
Q

a thicker convex lense will ….. focal lenght so the focal point is….

A

thick convex will shorten focal length so focal point is closer to the lens

83
Q

what is nearsightedness and how is it corrected

A

can see things that are close but not far away
image focuses before the retina
concave lens to fix

84
Q

what is farsightedness and how is it corrected

A

can see far away but not close
image focuses beyond the retina
convex lens to fix

85
Q

what is presbyopia and who does it effect

A

“old eye” - will affect most people as they get older
distance of near point increases (the point of the closest object your eyes can accomodate to)
due to hardening of the lens and weakening of the ciliary muscles
corrective lenses are needed for close activities such as reading
near point can get as far away as 4m

86
Q

rods and cones

how mnay of each and their roles in the visual system

A 
120 million rods
-low light (even one photon active)
-supports low acuity vision
-relatively sensitive to movement
6 million cones
-concentrated in fovea
-less sensitive to light (10s - 100s of photons)
-daytime and high precision vision
87
Q

visual pigment molecules have two components…

name them and what are they

A

opsin - large protein

retinal - light sensitive molecule

88
Q

when does visual transduction occur

A

when the retinal absorbs light and changes its shape

this is called ISOMERIZATION

89
Q

what happens after isomerization

A

it takes a while before a photoreceptors is ready to transduce light again

90
Q

what are the three adaptations that allow us to see under different lighting conditions

A

role of the pupil - (about 1 order of magnitude change)
photorecptors (rods and cones = two visual systems bascially)
isonmerization

91
Q

how many orders of magnitude does the light we see go over

A

9 orders of magnitude ie something can be 1,000,000,000 times brighter and we can still see it
our visual systme solves this problem by restircting the ‘dynamic range’ of its response to match the current overall ambient light level

92
Q

convergence in the retina

A

cones (6 to 1) - near one to one wiring
-ability to discriminate detail
-trade-off is that cones need more light to drive a ganglion cell response
120 million rods converge to just 1 million ganglion cells
rod system in the periphery more sensitive in low light due to higher convergence, but has lower acuity
cone system in fovea is less sensitive to light due to lower convergence but has higher acuity

93
Q

what do rods and cones do that helps them increase their sensitivity to wide ranges of light

A

adapt to become less sensitive to light as light levels increase = maintains a dynamic range of sensitivity

94
Q

explain psychophysics experiment measuring dark adaptation

A

measure detects thresholds as a function of time in the dark
-observer looks at fixated point but pays attention to a test light on the side
-this will project the light into the periphery of the retina where there are both rods and cones
can plot a curve of threhold against time in the dark

95
Q

the dark adaptation curve

A

down on the graph = higher sensitivity
gets more sensitive, flattens out at 5-10 mins
then gets even better

96
Q

what does testing rod monochromats help us learn about the dark adaptation curve

A

they only have rods
is a continuous curve down - none of this first wobble but then agrees with those with normal vision (so rods and cones)
so the cones do that first bit of sensitivity
so cones detect the dim light at first until rods take over

97
Q

talk through the demonstration of dark adaptation

A

dark spots - unisomerized molecules in cones (so are ready for photons)
in the dark all retinal molecules are ready for a photon
the photorecpetor is very sensitive to light
this is a good state for walking in the dark, but not if you walk outside
in bright light nearly all molecules are isomerized
the photoreceptors are not sensitive to light, now you are not overexposed but you cannot see in the dark
once back in the dark after 6 mins cones are ready but takes 20-30 mins for the rods

98
Q

path of info from rods

A

M-ganglion cell
Magno LGN
V1

99
Q

path of info from cones

A

P-ganglion cell
Parvo LGN
V1

100
Q

distinct pathways project…

A

to distinct destinations in LGN

101
Q

how do we visualse retinotopic maps

A

on flattened cortex

102
Q

cortical magnification on the fovea

A

fovera has more cortical space than expected
fovea accounts for 1% of the retina
singals from the fovea account for 8-10% of the visual cortex
this provides extra processing for high acuity tasks

103
Q

circle sweeps outwards

how is this projected in visual cortex - eccemtric map

A

wave of activtion moves from foveal representation to peripheral representation (posterior to anterior)

104
Q

polar angle map

A

wedge going clockwise round a circle like a second hand
contralateral mapping of visual field to cortex
inverted up and down

105
Q

how is V1 organised

A

left codes on right

106
Q

occular dominance columns

A

neurons in primary visual cortex initially repond best to one eye
neurons with the same preference are organized into columns
the columns alternate in a left-right pattern every .25 to .50 mm across the cortex

107
Q

single unit recordings in V1

A

shows orinetation selectivity in simple cells
bell curve showing best response shown to a particluar orientation
because of pattern of on centered receptive fields

108
Q

cells that orientate similarly

A

are next to each other

so push an electrode through and the cells it touches will all fire with similar orientation

109
Q

explain hubel and weisel’s model for the representation

A

ice cube model for the representation of orientation and ocular dominance
orientation columns across one edge
occular dominance columns on the other side alternating left and right

110
Q

what does an orientation map in V1 look like

A

reintopically organised - so map like

there are cells selective for each orinetation in each little chunk of the map

PSYC 102 - sensory (4 decks)

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