Perceptual Organisation

Question 1

Describe the binding problem

Answer 1

Perceptual organisation- combining distant elements and features into a coherent ‘whole;, for example how do we separate objects and background

how can we make sense of visual information even when there is minimal input? (dog)

Question 2

What does the Dalmatian dog “illusion” (?) demonstrate about perceptual organisation

Answer 2

People will always notice this Dalmatian when they see it again

Once an organised percept, always an organised percept: effect of experience

Question 3

What is the relevance of biological motion?

Answer 3

We have high level perceptual information regarding movement with minimal information

Also the effect of ‘knowledge’ or memory: we are very often exposed to moving bodies

Question 4

What two psychological mechanisms of perceptual organisation are mentioned?

Answer 4

Gestalt laws

Texture segregation

Question 5

What four neural mechanisms of perceptual organisation are mentioned?

Answer 5

• selective deficits
• grandmother cells vs assembly coding
• Anatomical connections
• Contextual modulation

Question 6

What art style emphasises this perceptual organisation?

Answer 6

pointillism- objects are defined by the grouping of individual dots of colour

Why do these dots for objects?

Question 7

Name the four ‘classic’ Gestalt laws

Answer 7

1) Proximity: parts are grouped when close together
2) Similarity: parts are grouped when similar (e.g colour, contrast, illuminance, shape)
3) Connectedness: parts are grouped when connected
4) Common fate: when objects move together

Question 8

Name a criticism of the law of 1) connectedness and 2) common fate

Answer 8

1) Isn’t connectedness just proximity?

2) isn’t common fate just similarity?

Question 9

Name something which demonstrates the gestalt law of common fate

Answer 9

Random dot kinematograms use similarity of motion to define objects by motion alone

Question 10

What is meant by the Gestalt principle of closure?

Answer 10

Convex (closed) shapes are preferred over concave

e.g ( ) ( ) ( ) ( )

Question 11

What other Gestalt law does the previous example go against? What does this demonstrate?

Answer 11

proximity: the convex brackets are further than the concave brackets

This demonstrates competition between Gestalt laws, in this situation closure ‘wins’ over proximity

Question 12

What is meant by the Gestalt law of collinearity?

Answer 12

also known as good continuation.

We tend to group elements together that are in the same direction/ orientation

e.g > < vs >

Question 13

An example was shown in the lecture where white objects were shown against black and the same black objects against white. In both scenarios the same objects were perceived but in different colours.

What allowed these shapes to have been seen as the ‘objects’ rather than the background?

Answer 13

The gestalt law of symmetry: contours that form a symmetrical shape are grouped over contours that form an asymmetrical shape

Question 14

What is meant by the gestalt law of pregnanz?

Answer 14

Also known as the law of good forms (pregnanz is german)

Preference for or reduction to the simplest forms

(olympic rings)

Question 15

What is a criticism of the gestalt law of pregnanz?

Answer 15

It is v similar to good continuation and closure

Question 16

What is meant by the Gestalt law of figure-ground?

Answer 16

Some region is figure, other is background that ‘continues’ behind figure

Question 17

What is meant by texture segregation?

Answer 17

Regarding gestalt principle of similarity, wanted to see how much features could differ before they were seen as separate objects

Question 18

name some ways in which elements could differ in order for it to be perceived differently

Answer 18

orientation, colour, size

Question 19

sometimes features differ but there is no immediately obvious segregation, what is this type of segregation referred to as?

Answer 19

pre attentive segregation

Question 20

What is useful about these ‘not segregating texture’?

Answer 20

They point out what features are and are not useful for segregation

Question 21

Would these symbols from the lecture be segregating textures?
⊿ ⇲
Why or why not

Answer 21

No, Both elements consist of the same orientations of line segments, only different in their relative position (‘relative phase’ in Fourier terms) > orientation matters, phase does not

Question 22

the lecture then displayed what appeared to be standing and lying 10s and 2s and five made up of lines. What rule of segregation did this demonstrate?

Answer 22

Both sets of elements (standing and lying 10’s vs 2&5’s) consist of the same orientations of line segments, only different in their relative position (relative phase in Fourier terms) > orientation group statistics matter

It looks at the horizontal vs vertical ‘energy’ (consistency, frequency(?))

Question 23

Through experimentation it has been found that what 6 features matter for segregation in regards to similarity?

Answer 23

• Orientation
• Direction of Motion
• Disparity (Depth)
• Spatial Frequency (Size)
• Luminance
• Color

Question 24

What disorder exists regarding this perceptual organisation?

Answer 24

Apperceptive/ Integrative agnosia

Patients see individual features, such as color, orientation or motion, but cannot integrate this into a whole, failure of perceptual organisation (can know what an object is through touching it but not through sight)

Question 25

What damage in the brain is responsible for apperceptive agnosia?

Answer 25

Right Hemisphere occipital / temporal / parietal lesions usually quite diffuse (e.g. CO damage). Not one area but likely communication between visual areas

Question 26

What five tasks can demonstrate whether someone has apperceptive agnosia?

Answer 26

Degraded letter task, Gollin picture task (perceptual organisation images like degraded letters and incomplete drawings)
Copying is also bad
Unusual views/ shading task (large shadows) is also bad

Question 27

What usually causes this type of brain damage?

Answer 27

Carbon monoxide poisoning because it can cause oxygen shortening. The posterior of your brain is more vulnerable to oxygen shortage than the rest of the brain

Question 28

What is the difference between apperceptive and integrative agnosia?

Answer 28

Integrative is more mild. Patients can copy but piece by piece. Unusual views test can vary.

Question 29

What task is often suitable for integrative agnosia

Answer 29

Overlapping objects are not seen individually

Question 30

Can patients with apperceptive and integrative agnosia recognise faces?

Answer 30

Yuh!

Question 31

What is meant by feedforward processing?

Answer 31

The information goes from lower regions to higher regions.

V1 is the starting point of projection to the other visual areas and the rest of the brain.

From there, activity spreads to the other visual areas.

Question 32

at what speed does this feedforward sweep occur?

Answer 32

Speeds through the visual system within 80 ms by means of feedforward connections from

Question 33

What information does this fast feedforward sweep provide? (3)

Answer 33

Provides the neurons with their receptive field tuning properties
•Provides fast detection of ‘hardwired’ features and feature constellations
•In that sense provides a set of grouping operations

Question 34

What unconscious process does this fast feedforward sweep then allow outside of the visual cortex?

Answer 34

This then enables ‘intelligent’ sensorimotor reflexes

Question 35

How often is there a “spike” and why is this significant regarding the fast feedforward sweep?

Answer 35

There’s only one spike per 10ms. The V1 cortex is activated around 40ms, other areas such as 7a, V3, MST etc is activated around 50ms and a range of other areas such as V2, V4 and even prefrontal cortex are activated around 65ms.

This means these areas are reached after only around 2/3 spikes.

Question 36

What trends are generally seen in the cells further on in the feedforward convergence? (2)

Answer 36

During this feedforward convergence, cells get increasingly larger receptive fields, and get progressively more complex tuning properties

Question 37

Why may neurons in V4 and other areas have larger receptive fields and more complex characteristics?

Answer 37

There are horizontal and feedback connections

Question 38

Therefore ________ are mediated by _________

Answer 38

RF tuning properties are mediated by the feedforward sweep

Question 39

How does this feedforward sweep seem to function in apperceptive and integrative agnosia patients?

Answer 39

In the apperceptive / integrative agnosia patient, this ‘feedforward sweep’ seems to function normally: he sees features like orientation, color, motion, and even faces. He just can’t make sense of the combination of these.

Question 40

How can these patients make sense of faces when they are made up of seemingly indefinite shapes and orientations?

Answer 40

apparently, to the brain, a ‘face’ is just as primary a feature as orientation, colour or motion is. Its detection is ‘hardwired’ into the feedforward convergence of visual information processing

Question 41

How would the fastforward sweep help you if someone threw a punch at you

Answer 41

The fast feedforward sweep enables the rapid extraction of ‘hardwired’ features and feature constellations, enabling swift visually guided action.
It forms a sort of ‘intelligent reflex arch’, enabling the execution of well trained, automatic, visually driven motor programs
This would mean that you might automatically go to dodge or block the punch.

Question 42

What also occurs in the ventral stream

Answer 42

Also in the ventral stream, fast recognition of important feature constellation occurs, enabling rapid extraction of (e.g. emotionally) relevant information

Question 43

Describe two paths the signals may go from the area V1 when translating visual input to action. How long does this take to occur approximately?

Answer 43

V1 > MT > Par > Mot

V1> V2 > V4 > TE > Mot

Mot > Action

Full sensory to motor cascade within ~ 120 ms

Question 44

How can these horizontals connections be observed?

Answer 44

Anterograde neuro-anatomical tracers (in this case Pha-L) are injected in a specific site, are taken up by cells, and via axonal transport reach all their axon terminals

Question 45

To what extent are cells connected to nearby cells,

Answer 45

Cells are mainly connected with nearby cells (short range horizontal connections) but also - more selectively- with more distant ones.(long range horizontal connections)

Question 46

What are meant by boutons?

Answer 46

Boutons indicate synaptic contact

Question 47

What did the tracing of horizontal connections combined with the visualisation of orientation columns (optical imaging) reveal

Answer 47

It turned out that long range horizontal fibers in V1 (layers 2/3, 5) selectively interconnect cells with the same orientation preference

Question 48

What gestalt law does this finding regarding orientations relate to?

Answer 48

This seems highly relevant for the observation that elements with the same orientation tend to group together perceptually (grouping by similarity)

Horizontal connections are the neural ‘substrate’ for the Gestalt law of grouping by similarity

Question 49

What further finding was there regarding these horizontal connections between orientation cells?

Answer 49

Further studies revealed that the horizontal connections in V1 tend to spread along a ‘line’

This line coincides with the orientation preference of the injection site, so that the horizontal connections seem to connect cells with the same orientation and lying along a line in visual space

Question 50

What other gestalt law does this finding apply to?

Answer 50

This type or collinear spread seems to be the substrate for the Gestalt law of ‘good continuation’ or ‘collinearity’, studied in contour grouping (also proximity)

Question 51

What detail given in the gestalt law of collinearity also coincided with findings regarding the orientation cells?

Answer 51

That this grouping perception is less effective when greater than around 30 degrees

Question 52

These connections existing are one thing, but how are these expressed in the activity of the cells?

Answer 52

Local gestalt grouping: V1 cells respond more strongly when orientations in the surround

Question 53

Where have similar findings to this been found and what do they consist of

Answer 53

Similar findings have been found in area MT, where most neurons are direction selective. Here, patchy horizontal connections connect cells with similar direction preference

Question 54

What gestalt law do the findings in area MT therefore correlate to

Answer 54

Gestalt law of ‘common fate’

Question 55

What is the role of feedback signals in V1?

Answer 55

Contextual modulation of responses; integrating information from the various cells to establish grouping perception, background and figure etc

Question 56

Describe in relation to time the information that is processed in area V1 from when the information enters the brain

Answer 56

40- 100ms: isolated information, cells only look at what happens within their RF (which is identical)
100 + ms: integrated information, V1 activity is modulated by global visual context

Question 57

Where can you look to see the modulation which reflects figure ground segregation?

Answer 57

The google doc of digital diagrams cuh, on the gang bruh

Question 58

How is it shown that contextual modulation reflects figure-ground organisation?

Answer 58

recording responses and having the RF go over a small square box against a background of another shade.

The responses will be stronger as the RF goes over the object, particularly the edges

Question 59

Describe what happens in the feedforward process at 50 ms, 70 ms and 100ms

Answer 59

50ms- Orientations processes by V1 (Low level feature detectors e.g orientation or motion, depth, colour etc)

70ms- Orientation info reaches extrastriate areas (High level feature detectors e.g convex shapes, squares etc)

100ms- Recurrent processing yields figure-ground segregation (through feedback into posterior areas) (low and high level feature information combines to form integrated percept of square made of orientated line segment)

Question 60

What proof is there for this feedback mediating V1 integration ?

Answer 60

Extrastriate area lesions abolish contextual modulation

Question 61

In regards to the processing mechanisms in the visual hierarchy what functions do a) feedforward connections b) Horizontal connections and c) feedback connections carry out?

Answer 61

Feedforward connections- Carrying orientation information

Horizontal information- Lateral inhibition between neurons tuned to the same orientation. Present at every level in the hierarchey

Feedback connections- These connections do a retinotopic feedback,

Question 62

The resulting activity in V1 therefore looks like this (kinda)
__/’—-‘\___
Explain in relation to these connections hhow this activity is recorded

Answer 62

The lateral inhibition between neurons tuned to the same orientation in horizontal connections creates the bumps. The retinotopic feedback of the feedback connections progressively fills in the region between the bumps.

Question 63

There were then studies which examined whether you could selectively inactivation these feedback connections while leaving the feedforward connections intact.

Describe these and the subsequent results

Answer 63

It proved difficult but it was found that these feedback and recurrent processing connections used a different neurotransmitter. When the NMDA receptor blocker, APV was applied seemed to restrict these processes while maintaining the feedforward connections.

Question 64

How were bottom up visual signals reduced?

Answer 64

By AMPA receptor blocker CNQX, but RP is not

Question 65

How are these findings relevant to conducting visual neuroscientific research on animals?

Answer 65

The NMDA receptors are much more sensitive to anaesthesia than AMPA receptors. Therefore you selectively lose the feedforward connections

Question 66

To what extent do the combinations of different feature contrasts combine to add to contextual modulation?

Answer 66

RECURRENT SIGNALS IN V1 REFLECT PERCEPTUAL ORGANIZATION OUTCOME Contextual modulation is present for every possible feature contrast, combination does not add

sorry for shouting

Question 67

How were these findings reflected in human studies?

Answer 67

(obviously couldn’t conduct the same experiments but…)
It was shown through either applying or not applying TMS at 100ms, 160ms or 240ms that the perception of Kanizsa squares ( four 3/4 circles depicting a square) requires feedback from LO to V1.

It was found that if you applied it at 100ms in the higher level LO people would lose the percept to an extent. This feedback then goes back to the earlier areas about 60 ms later and if you disrupt V1/ V2 then, you also lose the percept. If it was a constant feedforward movement, then you would expect the opposite result.