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Perception and Action > 5- Spatial Recognition > Flashcards

5- Spatial Recognition Flashcards

1
Q

what is a cells receptive field

A

a cells receptive field is the area on the retina which, when stimulated by light elicits a change in the firing rate of the cell

the effect of the stimulus can either be excitatory or inhibitory

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2
Q

what happens in single cell recording

A

An electrode, inserted into a neuron (e.g. V1)
measures electrical activity
• Activity is that of a SINGLE neuron

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3
Q

how do receptive fields increase in complexity

A 
photoreceptors
ganglion cells
LGN cells
simple cells
complex cells
hypercomplex cells
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4
Q

what is V1

A

visual cortex

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5
Q

what do V1 cells respond to

A

V1 simple cells respond to oriented bars and

edges

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6
Q

what did hubel and wiesel find

A

Hubel and Wiesel – found oriented bar detectors

in V1 of cats using single cell recording

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7
Q

what is a grating

A

patterns of black and white stripes

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8
Q

what is the tilt after-effect

A

Adapt to a pattern of tilted lines - stare for a minute
Test - a pattern of visual lines
Vertical pattern looked tilted in opposite direction to adaption pattern
Percieved isnt as much of a tilt - See it as tilted

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9
Q

what is the explanation of the tilt after-effect

A
  1. Orientation tuned neurons respond best to preferred orientation but also respond to other similar orientations

Vertically aligned receptive field
Response function of cell
Respond to preferred orientation and similar

Neuron in v1 - vertically orientated - strongest response vertical stimuli in the receptive field

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10
Q

how many components in tilt after-effects

A

3

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11
Q

what is the perceived orientation determined by

A

Perceived orientation determined by distribution of responses across cells

E.g. 7 cells in v1 - each have different preferred orientation
E.g. cell 7 - receptive field horizontally orientated - prefers horizontally organised stimuli

Visual system looks at distribution of responses across all cells and looks to where the peak is

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12
Q

what happens in adaption

A

cell’s response decreases following prolonged activity

All cells responding - their response decreases over a period of time - fatigues

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13
Q

what are the 3 components of tilt after-effects

A

3 components:
1. Orientation tuned neurons respond best to preferred orientation but also respond to other similar orientations

  1. Perceived orientation determined by distribution of responses across cells
  2. Adaptation – cell’s response decreases following prolonged activity
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14
Q

what happens in the tilt after-effect

A

Before adaptation the line looks vertical
Start of adaptation tilted line looks tilted
During adaptation tilted line continues to look tilted, but cells’ responses decrease
After adaptation vertical line looks tilted due to asymmetrical response distribution

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15
Q

why does the tilt after-effect happen

A

Even though viewing vertical patten - distribution of responses has shifted
Peak moves
See a tilt in opposite direction

Expected after adapted
Caused a reduction in the response of 3,4
Cell 2 wasn’t adapted by adaptive pattern
Cell 2 responding similarly - the peak

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16
Q

what does the size of after-effect depend on

A

Size of after-effect depends on difference between adapt and test

Depends on difference between adapt and test
Adapt - reduced range of cells - causing cells 4,5 to adapt , 3 isnt adapted due to difference
When go back to viewing the trust the peak of distribution doesnt change
When big difference dont get big after effects

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17
Q

what curve is the after effect

A

sine wave curve
Peak around 10-20 degrees of adapting pattern
When adaptation gets further away to 45 degrees
Get less of an effect

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18
Q

what would happen when 45 degree tilt

A

45 degree tilt
Peak wouldn’t shift too much
Smaller after effect in clockwise direction

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19
Q

what happens in a 20 degree anti-clockwise tilt

A

Big after effect in opposite direction
Anti-clockwise tilt - clockwise after effect
20 degrees tilt

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20
Q

what is the peak effect

A

Peak around 10-20 degrees of adapting pattern
When adaptation gets further away to 45 degrees
Get less of an effect

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21
Q

what does the tilt after effect provide evidence for

A

Tilt after-effect provides evidence for orientation tuned cells in human visual system

Psychophysics

Measure what people perceive

Make inferences about visual processes

Orientation tuned cells in visual system

Cant do single cell recording in humans so tilt after effects eviden ce that operates in same way as cats and monkeys

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22
Q

Cats and monkeys have cells with different sized receptive fields at each orientation… is the same true of humans?

A

yes
Different cells in v1 have different orientations and different size of receptive field
Respond best to different sizes of line
Receptive fields sizes vary but all have a preferred orientation

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23
Q

is the after-effect opposite to what you adapted with

A

yes

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24
Q

what happens before adaptation

A

Before adaptation size perceived veridically

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25
Q

are cells tuned to different sizes and width of lines

A 
Cells are all tuned to vertical lines but different sizes and width of lines
1- skinny lines
7- fat lines
3 - perfectly matches receptive field
2,4, weaker response
1,5,6,7 dont respond
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26
Q

wha happens in adaptation

A

adapt to fatter bars
During adaptation cells’ response decreases
After adaptation lines look thinner due to
asymmetrical response distribution
Perceive narrower bars than what actually there bc peak is on the thinner side

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27
Q

what does tilt after-effect provide evidence for

A
  • Tilt after-effect provides evidence for orientation- tuned cells in human visual system
  • Size after-effect provides evidence for size-tuned cells in human visual system
28
Q

are size and orinetation fundamental parts of the viusal scene

A

Size and orientation are fundamental features of parts of the visual scene and the brain has cells tuned to these features

29
Q

what do we mean by size

A

ambigous
“Serious scientists do not, we are told, refer to bars as fat or skinny. Rather they define the size of these bars in terms of the number of bars that would fit in a given distance, so

big bars actually have what is called a low spatial frequency
skinny bars have a high spatial frequency

… (This makes the topic much more boring and much less clear and therefore the people who use these terms are much more important. So obviously we’re going to talk about spatial frequency from now on).”

30
Q

If a cell responds strongly to a given stimulus, how will the cell’s response change following prolonged exposure to that stimulus?

A

response will decrease

31
Q

After prolonged exposure to an adapting bar rotated 45 degrees away from vertical (clockwise), a subsequently viewed bar which is physically vertical will appear:

A

approximately vertical

32
Q

what is spatial frequency

A

number of bars per unit distance (usually cycles per degree)

33
Q

in fat bars how mant cycles per degree

A 
Far bars
One cycle per degree 
Peak white
Trough black
One unit of distance on the retina
34
Q

how many cycles per degree in skinny bars

A

2 cycles per degree
Fit more bars in same difference on retina
2 cycles per degree

35
Q

what frequency are fat bars

A

Fat bars = low spatial frequency

36
Q

what frequency are thin bars

A

Thin bars = high spatial frequency

37
Q

how do you define size of a feature on retinal image

A

spatial frequency

38
Q

do natural images contain information at many spatial frequencies

A

yes

Natural images contain information at many spatial frequencies

39
Q

what are high spatial frequency

A

fine details

40
Q

low spatial frequency

A

course information

41
Q

how do we filter spatial frequency in images

A

Filter image to extract certain spatial frequencies
Filter out spatial frequencies

Picked out fine details - high spatial frequency carries out e.g. eyes nose mouth - thin lines - high spatial frequency

Low spatial frequency - shading - fatter bars - big features

42
Q

what is high contrast

A

big difference between light and dark

43
Q

wht is low contrast

A

Only varies from slightly darker from mid grey and lighter mid grey here

44
Q

at high contrast what spatial frequency can you see

A

High contrast see all different spatial frequencies

45
Q

at low contrast and low spatial frequency

A

cant see bars

46
Q

and low contrast

A

cant see any bars

47
Q

do we have equal spatial contrast sesnitivity

A

Not equally sensitive
Sensitivity - how low turn contrast and still be able to detect
As change spatial frequency of pattern - sensitivity varies
Low spatial frequency - low sensitivity
Mid - sensitive to intermediate spatial frequencies
High - lower sensitivity

48
Q

when do we have greater sensitivity

A

We have greater sensitivity to intermediate spatial frequencies. They can be perceived at low contrasts

49
Q

what are spatial frequency channels

A

Spatial frequency channels – collections of neurons tuned to the same spatial frequencies (i.e. respond to the same range of spatial frequencies)

50
Q

what happens when spatial frequency too high

A

Spatial frequency too high - no longer have cells that can rspond - no receptive fields small enough - details become invisible to us bc aren’t sensitive

51
Q

what happens when we recognise

A

Recognise - high spatial frequency information carry fine details allowing us to recognise her face - fine details in face

52
Q

what happens when far away

A

Far away - high spatial frequency - invisible to us - no longer able to recognise far away - information we need is invisible to us
Spatial frequencies get bigger on retina - range with which you can perceive
Spatial frequency gets lower when closer

53
Q

what happens in the periphery

A

receptive field sizes increase

This means contrast sensitivity varies with eccentricity - we can’t see high spatial frequencies in the periphery

54
Q

fovea

A

Fovea - central party of retina - densely packed with cones - good visual acuity - good at picking up intermediate spatial frequencies and high sensitivities

55
Q

periphery of retina

A

Periphery of retina - cells have bigger receptive fields- spatial frequencies sensitive to get lower - lose ability to detect high sensitivity

56
Q

far periphery

A

Far periphery - only detect very low spatial frequencies

Receptive field gets bigger as move to periphery

57
Q

spatial contrast sensitivity function

A
  • Receptive field sizes increase in the periphery
    • This means contrast sensitivity varies with eccentricity - we can’t see high spatial frequencies in the periphery
    • Therefore acuity is poorer in the periphery
58
Q

how is spatial frequency processed by the visual system

A

When images processed by visual system, information at differing spatial frequencies carried by separate channels

Different cells in primary visual cortex
Processing in channels that are all processing different spatial frequencies

59
Q

retinal vs real size

A

Spatial frequency tells us about size on the retina – it does NOT indicate real size in the world since the projected size depends on distance

any line on the retina could have been produced by infinite different lines in the world

60
Q

what does spatial frequency tell u

A

size on the retina

61
Q

retinal vs real size

A

Bars of different widths at different distances can project to same SF on retina

62
Q

what did Burbeck do

A

Can we perceive both retinal and real size?
• Stimuli 1 & 2 at different distances from participant
• Discrimination experiment - which stimulus has thinner bars?
• Discriminating retinal size – task very hard
• Discriminating real size – task easy
• Conclusion – conscious perception in terms of real size

63
Q

what is size constancy

A

Size constancy: we perceive an object’s real size in the world regardless of distance

64
Q

what is orientation constancy

A

we perceive an object’s orientation in the world regardless of the orientation on the retina

65
Q

why is it hard to draw a 3D object

A

No conscious access to retinal image properties explains why drawing a 3D object or scene can be such a challenge
retina - 2D representation

66
Q

what are images composed of

A

Images are composed of lines and edges of differing orientation, size and contrast.

67
Q

what is the visual image processed by

A

The visual image is processedby neurons tuned to orientation and spatial frequency

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