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Visual Motion Processing Flashcards

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1
Q

What is motion good for

A

Motion based image set

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2
Q

What is motion good for?

A
  • motion based image segmentation
  • navigation
    -depth from motion
  • structure from motion
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3
Q

Motion is being computed in the brain

A

Directly and indirectly

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4
Q

Indirect methods of motion capture

A

Independent analysis of spatial displacements and temporal intervals

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5
Q

Indirection methods of motion are used

A

When there are few objects/features or long intervals and large displacements

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6
Q

Direct method of motion capture

A

Specialized detectors used to compute motion directly from intensity variations in the retinal image without feature tracking

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7
Q

Motion perception remains possible with

A

Sub threshold spatial and temporary displacements

Brief, high density displays which preclude cognitive tracking of features

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8
Q

Motion sensitive receptive fields

A

Luminance profiles of moving contours that are oriented in space time

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9
Q

Detecting motion is analogous to

A

Extracting spatial orientation

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10
Q

Some V1 cells have receptive fields which are oriented in space time which

A

Respond strongly to oriented edges moving in a preferred direction, but not at all in the opposite direction

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11
Q

Within the Reinhard model of motion detection, receptive fields sample

A

Two adjacent points in space (neurons a and b)

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12
Q
A
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13
Q
A
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14
Q

Within the reichardt model
of motion detection, moving stimulus activates

A

Each of the neurons in turn

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15
Q

Within the Reichardt model of motion detection, the output of one of the neurons

A

Was delayed relative to the other

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16
Q

Within the Reichardt model of motion detection, if internal delay matches time it takes for stimulus to move between receptive fields, the detector

A

Will signal rightwards motion

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17
Q

Within the Reichardt model of motion detection, movement in opposite

A

Direction gives no response

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18
Q

Limitations of local motion analysis

A

Aperture and speed selectivity

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19
Q

Local motion detectors in V1 only see a small part of the image and

A

Respond to motion orthogonal to luminance edges

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20
Q

As a result the output of any one motion detector may not be a valid indicator

A

Of the overall direction an object is moving

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21
Q

The solution to the aperture problem was to

A

Combine the responses of detectors with receptive fields located in different regions in space

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22
Q

Speed is the ratio of

A

Temporal frequency and spatial frequency

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23
Q

Local motion detectors in V1 respond to

A

One particular combination of spatial frequency and temporal frequency, rather than to all stimuli moving at a particular speed

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24
Q

The solution is to combine the output detectors

A

that respond to the same speed

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25
MT neurons have large receptive fields,
Receiving input from many V1 neurons
26
Whereas V1 neurons only respond to a particular orientation moving in a particular direction, MT neurons respond
To a preferred direction independent of pattern
27
Many more neurons in MT
Also show proper speed tuning than in V1
28
Neurons in the medial superior temporal area have particularly large receptive fields and
Respond selectively to complex optic flow patterns
29
Neurons in the superior temporal sulcus
Respond selectively to biological motion
30
Regions in the intra parietal sulcus and lateral occipital sulcus have
Been implicated in the extraction of structure from motion by fMRI studies
31
Repeated stimulation in the preferred direction reduces
The responsibility of direction selective V1 neurons
32
Adaptation reduces the response of neurons to stimuli at all contrast levels, but shifts
The contrast response function laterally for others
33
Adaptation to drifting gratings produces a mixture of ________ ______and _______ _______ changes neutrons
Response gain and contrast gain
34
These effects disappear when adapting and test stimuli were presented
In different sub regions of the receptive field
35
The disappearance of the response gain and contrast gain suggests that effects of adaptation are
Likely inherited from earlier levels
36
Priebe et al 2002
Measured adaptation of MT cells over shorter timescale
37
Following the onset of motion MT neurons display an initial transient peak in firing rate
that decays to a sustained level over ~100ms
38
The reduction in MT neuron responsiveness is maintained when stimuli are
Moved to different sub regions of the receptive field, suggesting that it’s not inherited from V1 inputs
39
Motion adaptation produces change in
Sensitivity and biases that mirror those seen following adaptation to static stimuli
40
Contrast sensitivity is reduced
for gratings moving in the adapter direction, but not in the opposite direction (Sekuler & Ganz 1963)
41
Direct after effect
Adaptation to a given direction of motion produces repulsive biases in the perceived direction of subsequently viewed stimuli (Levinson & Sekuler 1976)
42
The motion after effect (waterfall illusion)
After adaptation to a given direction of motion, static or flickering objects appear to move in the opposite direction
43
Waterfall illusion was known to the
Ancient Greeks
44
Waterfall illusion was first reported in modern times by
Robert Adams (1834)
45
Examples of the motion aftereffect
Spiral optical illusions, Starry Night painting
46
Explanation of the motion after effect
Distribution shift model
47
Distribution shift model was developed by
Mather, 1980
48
With the distribution shift model, prior to adaptation a static test pattern produces similar responses
From motion selective neurons tuned to all directions
49
Adaptation selectively reduces neural responsivity to the adapted direction, causing a
Shift in the distribution of responses to the test pattern
50
Traditionally investigations of motion after effects use static test patterns
And measure the duration of the illusory motion perception
51
Using static test patterns the motion after effect displays a number of properties consistent
With adaptation at an early stage of local motion processing
52
Location specificity
Adapting at one retinal location doesn’t result in a MAE at other locations (Masland 1969)
53
Partial interocular transfer
Switching eyes between adapting and test periods reduces the MAE but doesn’t abolish it (Moulden 1980)
54
Spatial frequency tuning
Strongest MAE is elicited when the adapting and test stimulus have similar spatial frequency (over et al 1973)
55
56
Temporal frequency tuning
Strongest MAE obtained at a constant temporal frequency (~8Hz) regardless of stimulus spatial frequency (Pantle 1974) not tuned to speed
57
An alternative way to measure the motion after effect is to test
With a moving or flickering test stimulus and try to null the percept of illusory motion
58
Stimuli shown here have been constructed by adding
Together upwards and downwards drifting gratings with different contrast balances
59
In the absence of adaptation equal component contrasts gives rise to the perception
Of counter phase flicker (no net motion-participants equally likely to say up or down)
60
The strength of the motion after effect can be quantified by
Measuring the shift in this null point after adaptation in a given direction
61
The dynamic motion after effect shows several characteristics consistent with
Adaptation at a higher stage of processing where loc motion signals are integrated
62
Low positional specificity
Adapting to one retinal location induces motion after effect at remote spatial locations, particularly when complex optic flow motion used (Snowden & Milne 1997)
63
Complete interocular transfer
Similar magnitude dynamic motion after effects obtained when testing the non adapted and adapted eye (eg Nishida, Ashida, Sato 1994)
64
Speed tuning
Magnitude of the dynamic motion after effect is tuned to speed, the ratio of temporal frequency to spatial frequency (Ashida & Osaka 1995)
65
66
Differing properties of static and dynamic MAEs has given rise to the suggestion
That they may reflect adaptation at local and global stages of motion processing
67
Jordan Fallah and Stoner (2006) found that observers adapted to
Biological motion stimuli which distinguished men from women
68
Jordan Fallah and Stoner (2006) found that adaptation to the gate of one gender biased judgements of subsequently
Viewed gates towards the other gender
69
Jordan Fallah & Stoner (2006) found that randomizing the phase of each individual dots motion significantly
Reduced the size of the effect suggesting that it wasn’t solely due to local adaptation
70
The functional role of motion adaptation in the visual brain
Remains far from clear
71
Suggestions for what the function of motion adaptation include
Improve discriminability, improved efficiency, normalization
72
Improved discriminability as a possible for function of motion adaptation
Adaptation had been shown to improve speed discrimination in humans (Clifford & Langley 1996) and monkeys (Krekelberg, van Wezel & Albright 2006), however these effects are modest
73
Improved efficiency as possible function of motion adaptation
Many researchers believe that adaptation improves the efficiency of the neural code by equalizes response levels over time and reducing redundancy
74
Normalization as possible function motion adaptation
Meaning motion adaptation acts to recalibrate the zero velocity point (Harris Morgan & Still 1981)

The Visual Brain (2 decks)

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