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perception Flashcards

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1
Q

What is contrast and how does it track over the lifespan

A

It declines with age - around or 60s
Differences in luminance over a scene
Can be very debilitating if lost

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2
Q

Where is contrast processed

A

Retina
LGN
Cortex

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3
Q

What is luminance and how is it measures

A

Measure of energy emitted or reflected by a light source

Measured by candelas per sq metre (CD/M2)

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4
Q

What is michelson contrast

A

Maximum luminance - minimum luminance / average luminance

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5
Q

What is a linear receptive field

A

The region of space where changes in luminance influence the activity of a single neutron
It is linear as excitatory and inhibitory are summed
Neurone respond to stimuli they are tuned in for

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6
Q

Why do we get the Hermann grid illusion

A

We see the little grey dots in the intersections as there is a smaller neuronal response
When we focus on the intersection the smudge is not visible- we can resolve details with more accuracy at the centre of our vision

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7
Q

What are v1 simple cells tuned in for

A

Tuned in for orientation

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8
Q

v1 complex cells?

A

2 linear filters are squared and summed

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9
Q

What is the LGN characterised by

A

Gain control mechanisms

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10
Q

What is cortical processing characterised by

A

Nonlinear processsing

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11
Q

Hierarchy of processing

A

Receptors
Neuron transmit info
Thalamus (relay station)
Cortical processing

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12
Q

What is electrophysiology

A

Fine wires are inserted into areas of interest
It had high spatial selectivity
We can measure cells in real time

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13
Q

Ventral pathway?

A

“What”
LGN to temporal lobe
Object processing and fine detaol

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14
Q

Dorsal pathway?

A

“How”
LGN to parietal lobe
Motion and spatial processing

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15
Q

Where is colour coded

A

V4

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16
Q

Where is motion coded

A

V5/MT

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17
Q

What happens if there is damaged to v4

A

Can’t perceive colour

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18
Q

What happens if there is damage to V5/Mt

A

Can’t process motion

Couldn’t cross road

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19
Q

Experimental evidence for maps in the brain?

A

A dye was attached to structures to show where a stimulus is represented in an area of the brain
Monkeys

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20
Q

What are some experimental techniques used when investigating cognitive processes

A 
Psychophysics
Single cell recording (electrophysiology)
fMRI
EEG
Adaptive optics
Optical imaging
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21
Q

What type of data comes from psychophysics and some techniques used?

A

Behavioural data not neural

Method of constant stimuli, method of limits, method of adjustment, staircase procedure

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22
Q

What can the method of constant stimuli tell us / what term is used to describe this

A

It is measuring how well people can discriminate between 2 lines
The threshold for detecting differences in the position of 2 lines was smaller than the width of a photoreceptor
Termed hyperacuity

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23
Q

Why continue to do psychophysics instead of collecting neural data

A

Neural data is expensive and takes time
Linking propositions more complex for neural data
Psychophysics and neuro imaging are complementary

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24
Q

Paradigms for fMRI

A

Block design: neural activity is compared when stimulus is present or absent
Event related: neural activity at a certain time after stimulus is presented. Compared across conditions
Combined: make inferences about substrates of human behaviour

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25
2 cortical surfaces
Sulci- dark grey concave | Gyri- light grey convex
26
Periperternal space?
50-100cm in front of you- you can discriminate object in depth really well Within this zone you are using binocular disparity
27
What is occlusion
We know 2/3 of things don’t exist - it is hiding behind another object
28
What is size constancy
You know how big an object should be | Don’t think someone is shrunk just because they are fair away
29
What is the Ames room
An optical illusion | We used cues from the room and it shows us the kids are two different sizes when they are actually the same size
30
What is the ponzu illusion
We assume the lines are getting smaller as they are further away but they are actually the same size We misapply size constancy and what we know about depth Kids in western societies more likely to see this than non western
31
Occlusion and size constancy are what type of clues
Contextual clues - create context about a scene
32
What are monocular vs binocular cues
Monocular- we use one eye | Binocular- Info is combined from both eyes
33
What type of cue is motion parallel and what does it do
It is a monocular cue Used for depth ordering Objects move around us as we move Angle small for distant object, wide for close object
34
What is binocular disparity
The difference between the left and right eye relative to the plane of fixation (heropter)
35
What is crossed / uncrossed disparity
Objects prior to our plane of fixation have disparity crossed Objects beyond our plane of fixation have disparity uncrossed
36
Name 2 sensor intro cues
Accomodation and vergence
37
What is accomodation
Changing focal length using ciliary muscles to calculate distance of object Relaxed muscles for things further away Tightened muscles/ squeezed to focus on something closer to you
38
What happens with accomodation and age
As we age our lens becomes less flexible, so we can’t adjust our focal length Can’t accomodate to objects of different distances
39
If you can’t accommodate your lens you may end up with
Long sighted vision (hyperopic eye) | Short sighted vision (myropic eye)
40
What lens would u use to correct for a hyperopic eye
Convex
41
What lens would u use to correct for a myopic eye
Concave
42
What is convergence
Angle of gaze of two eyes When something is further away eyes move inward, angle of convergence smaller When something is closer, angle of convergence is larger
43
What is strabismus
Misalignment of eyes often caused by different muscle tension Exotrope- eye moves outward Esotrope- eye moves inward Can be fixed with surgery If not fixed within a critical period can result in damages to contrast sensitivity and binocular depth perception
44
What is stereo good for
Fine motor control | Sewing surgery picking berries
45
What is disparity good for
Useful for testing stereo vision VR Movies Hugh risk jobs
46
2 limits imposed by vision
1. People use binocular and monocular cues. But VR relies on binocular cues so people with compromised stereo may just see 2 displaced images 2. We only have high resolution at the place we are looking at In natural environments we are always changing our focal planes as we move around but you can’t do that with VR. This causes headaches eye fatigue bc our vision is forced to combine cues that aren’t normal
47
What does Reinhardt model comprise
Spatial and temporal filters
48
Why is energy model better than reichardt
``` It has an extra step which allows quadrature pairs to be squared and summed to calculate motion energy and have responses oriented in time and space Less fussy than reichardt mode More specific More flexible Can detect more complex motion ```
49
Why does the aperture problem happen
Completion between local and global features of a scene | The motion is featureless - any pattern looks like any other part
50
How to solve aperture problem
Orientation info can disambiguate edges Changing the orientation of aperture can change its direction of motion If vertical, lines go up and down If horizontal lines go left to right or right to left
51
What can form information do
Can generate or disambiguate motion
52
How does form information generate perception of motion
Glass pattern- dots have no correspondence (no motion) Within 10-15 frames people detect motion Thought to happens bc dot pairs simulate motion streaks
53
Biological motion?
People see a person walking just bc of light points of joints Used high level constraints (our idea of what a person should look like) on low level info (dots)
54
How much of visual cortex devoted to visual processing
1/3
55
2 components of hand movements?
Planning phase | Guidance phase
56
What happens in planning phase
Visual info about target and hand plot course of action | Plot action trajectory, velocity movement plan to make movement as accurate as possible
57
What happens in guidance phase
You compare your hands location to the target, which you can use to update the movement plan to be more precise In acceleration stage, movement plan dominanates velocity and trajectory In deceleration phase, plan is subservient to updating information
58
4 limiting factors on performance
Bio mechanical costs Risk Visual error Motor error
59
What are bio mechanical costs
Energy expenditure involved when making movements and muscle stress involved
60
Risk
Sometimes a cost to making an inaccurate movement | Surgery picking berries
61
Motor error/ Fitts law
Speed accuracy tradeoff Less accurate with fast movements More accurate with slow movements bc you have time for feedback
62
What does movement depend of
Visual quality and associated error
63
2 things to minimise visual error
Light is better to see the target | Still targets- but doesn’t happen much in real life
64
What is online control of movement
When u alter motor plan based on the discrepancy between predicted and real feedback
65
How many milliseconds to update a slow reach
110-150
66
Are movements ballistic
No - we can use visual information throughout our reach to update performance to be more accurate
67
How do we know the posterior parietal cortex plays a role in online correction
Through TMS experiments (trans cranial magnetic stimulation) Electric magnetic coil placed on scalp where the target region lies It disrupts nerve cells in target region Movements and points are less accurate
68
What is developmental coordination disorder
Clumsy kids have trouble with fine motor skills- sport and writing What causes it unclear Probs due to deficits in visual and motor mapping Maybe Dorsal impairment
69
What happens with parietal damage
Often caused by stroke Sometimes can lead to visual neglect You only attend to one side of the visual field You are unaware of this tho
70
2 common eye movements ?
Saccades and smooth pursuit
71
Reaches are planned in .... coordinates??
Eye centred not arm centred
72
What are saccades
Eye movement characterised by rapid acceleration to a new location Occur 3 x per second Allow us to go rate points of interest
73
What are smooth pursuit eye movements
Tracking movement Characterised by constant velocity at the same speed of target Allow us to track an item of interest (often seen with a saccades) and then tracked with smooth pursuit
74
What drives saccades to be the same
The spatial temporal tuning of perception and mechanisms
75
Why should we move our eyes
``` The fovea (part of retina) contains central vision that has the highest density of photoreceptors and largest overlap of receptive fields The more photoreceptors to receive sensory input, the more info is available to process, results in high acuity ```
76
What did Yarbus 1967 find
Participants looked at photos and were given instructions such as “look at how weatlthy the ppl are in the photo” Questions guided where people’s fixated on Ppl looked at faces then objects in room Showed saccades are not random
77
What is the sequential information maximisation model
After each fixation the next fixation will be at a location that minimises uncertainty and maximises info
78
Distance between 1st saccades and hand?
1.5 degrees
79
How is the superior collicukus involved in selecting a new target
It mediates target selection Mid brain structure, integrates visual, auditory and somatosensory spatial info to intimate orienting movement of hand and eyes Part of circuits for visual processing and deployment of saccades Info is combined to become a single type of info
80
What happens when frontal eye fields are stimulated
Results in an automatic deployment of covert attention which improves performance Ability to select a target is decreased is superior collicukus is inactive
81
5 key points about bottom up attentional deployment
1. Stimuli depends on context e.g. colour can depend on what colour is next to it 2. Saliency map plausible and efficient bottom up strategy 3. People tend to move on from a spot and not return (inhibition of return) 4. Attention and eye movements tightly coupled- poses computational challenges to coordinate system used to control attention 5. Seeing and understanding an object makes you look it it for shorter time or longer time (longer if u don’t recognise it)
82
Top down pathways?
You have a cognitive goals in mind to do something e. G. Pick up water bottle
83
Bottom up control
A stimulus had a feature that captures our attention | You make a saccade and attend to it

Perception and Cognition (4 decks)

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