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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
what is weber's law
detectable change n a stimulus varies as a function of baseline stimulus value -constant ration (difference threshol / baseline value)
26
how did Fulton 1928 study walters brain
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
27
how does fMRI work
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
28
uses of functional meuroimaging
``` functional brain mapping relative neural activity behabiour -intact humans -patients with brain damage presurgical planning - eg epilepsy or tumour resection ```
29
problem with fMRI
no temporal resolution - spike appears around 6 seconds after stimulation but its really safe in humans
30
when do we use single unit recording and what does it measure
as usually surgical normally in non-humans occasionally used in humans for presurgical mapping measures firing in one neuron
31
evaluation of single unit recording
perfect temporal and spatial resolution but is only one sample at a time. would have to do it LOADS to be useful
32
explain multi--unit recording
utah ray rests ontop of the cortical surface several hundred neurons can be measured at a time
33
basic overview of neural connectivity
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
34
what does the ..... do | cell body
widest part of the neuronal body, contains the nucleus and other basic machinery common to most cells
35
what does the ..... do | dendrites
thin branches extending from the cell bisy that recieve signals from other neurons (INPUT)
36
what does the ..... do | axon
a thin tube extending from the cell body that carries electrical impulses away frm the cell body to other cells (OUTPUT)
37
what does the ..... do | myelin sheath
an insulating coating that surrounds some axons that can speed the transition of neural impulses down the axon by attenuating leakeage of current
38
what does the ..... do | axon terminal
the end of the axon, where neurotransmitters are released to communicate with other cells
39
what does the ..... do | synapse
the space between the axon terminal and another neuron's dendrite or cell body
40
how does a neuron send a signal to another neuron and explain
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
41
roughly how big are synapses
20nm
42
define neurotransmitters
chemicals that are released from the axon terminla that cause changes in the electrical potential of the receiving neuron
43
describe the chemistry at rest of a neuron
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
44
what happens to a neuron when there is an excitatory input from another neuron explain the whole process
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
45
what does the myelin sheath make possible and why
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
four important general observations about action potentials
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
neurotransmitters are......
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
what do excitatory transmitters do and give an example
cause depolarisation post synaptic neuron becomes more positive increases the likelihood of an aciton potential glutamate
49
what do inhibitory transmitters do and give an example
cause hyperpolarization post-synatpic neuron becomes more negative decreases the lieklihood of an action potential GABA
50
why is excitatory and inhibitory neurotransmitters important
it makes it possible to create neural circuits that can detect very specialised patterns of external stimulation
51
explain spatial summation
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
explain temporal summation
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
what is the parietal lobe responsible in senses
skin senses
54
what is the temporal lobe responsible in senses
hearing
55
what is the occipital lobe responsible in senses
vision
56
what are cones specialised for
daulighy colour vision, good detail
57
what are rods specialised for
night grayscale vision, poor detail
58
what is the principle underlying why there are different parts of the visual system
principle of modularity or functional specialization
59
gamma waves have..... wavelength whereas radio waves have....
gamma - short | radio - long
60
which colour has shorter wavelengths? blue or red
short - blue | long - red
61
frequency =
speed/wavelength
62
what is the speed of light
299 792 458 m/s
63
what does the cornea do
focus light onto retina
64
what does the cillary body do
ring of muscles around the lens (stretches and widens the lense)
65
explain how light get transduced and sent to the brain and what cells are involved in the right order (and how they are organised)
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
what lateral connections are provided in the visual system
``` horizontal cells (linked to photoreceptors) amacrine cells (linked to bi-polar / ganglion cells) ```
67
do we see with photoreceptors
no - they transduce | we dont even have access to the signals they produce, its the ganglion cells which talk to the brain
68
whats special about the fovea
fovea - pit | has ganglion and bipolar cells peeled away to provide direct light access to the cones
69
where in the eye are there no photorecptors and why
the blindspot | this is the area where the optic nerve leaves the eye
70
what is special about octups, squid and terrestrial gastropods etes
they have photoreceptors on the "correct" side of the retina. they have no blind spot
71
how is the retina organized and so what is the receptive field
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
how do we measure receptive fields
by monitoring single cell responses | stimulus is presented to retina and respons of cell is measured using an electrode
73
explain Hubel and Wiesel's experiment
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
what can we measure to understand what signals are being sent to the brain
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
explain how an excitatory center, inhibitory surround works
light targetting centre = more action potentials fired | if inhibtory surround is also fully stimulated then decrease in action potentials fired
76
explain the seven-receptor neural circuit underlying a centre- surround receptive field
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
What is Macular degeneration
fovea and small surounding area are destroyed creates another blind spot on the retina most common in older individuals
78
what is retinitis pigmentosa
``` genetic disease rods are destroyed first foveal cones can also be attacked sever cases result in complete blindness tunnel vision at first ```
79
what is Glaucoma
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
what parts of the eye focus light on the retina and to waht extent
cornea - 80% | lens - 20%
81
if the light source is far away the focal point is ......
closer to the lens
82
a thicker convex lense will ..... focal lenght so the focal point is....
thick convex will shorten focal length so focal point is closer to the lens
83
what is nearsightedness and how is it corrected
can see things that are close but not far away image focuses before the retina concave lens to fix
84
what is farsightedness and how is it corrected
can see far away but not close image focuses beyond the retina convex lens to fix
85
what is presbyopia and who does it effect
"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
rods and cones | how mnay of each and their roles in the visual system
``` 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
visual pigment molecules have two components... | name them and what are they
opsin - large protein | retinal - light sensitive molecule
88
when does visual transduction occur
when the retinal absorbs light and changes its shape | this is called ISOMERIZATION
89
what happens after isomerization
it takes a while before a photoreceptors is ready to transduce light again
90
what are the three adaptations that allow us to see under different lighting conditions
role of the pupil - (about 1 order of magnitude change) photorecptors (rods and cones = two visual systems bascially) isonmerization
91
how many orders of magnitude does the light we see go over
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
convergence in the retina
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
what do rods and cones do that helps them increase their sensitivity to wide ranges of light
adapt to become less sensitive to light as light levels increase = maintains a dynamic range of sensitivity
94
explain psychophysics experiment measuring dark adaptation
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
the dark adaptation curve
down on the graph = higher sensitivity gets more sensitive, flattens out at 5-10 mins then gets even better
96
what does testing rod monochromats help us learn about the dark adaptation curve
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
talk through the demonstration of dark adaptation
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
path of info from rods
M-ganglion cell Magno LGN V1
99
path of info from cones
P-ganglion cell Parvo LGN V1
100
distinct pathways project...
to distinct destinations in LGN
101
how do we visualse retinotopic maps
on flattened cortex
102
cortical magnification on the fovea
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
circle sweeps outwards | how is this projected in visual cortex - eccemtric map
wave of activtion moves from foveal representation to peripheral representation (posterior to anterior)
104
polar angle map
wedge going clockwise round a circle like a second hand contralateral mapping of visual field to cortex inverted up and down
105
how is V1 organised
left codes on right
106
occular dominance columns
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
single unit recordings in V1
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
cells that orientate similarly
are next to each other | so push an electrode through and the cells it touches will all fire with similar orientation
109
explain hubel and weisel's model for the representation
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
what does an orientation map in V1 look like
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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