Task 5: Mechanisms of Middle- and High- Level Vision

Question 1

Middle vision

Answer 1

loosely defined stage of visual processing that comes after basic features have been extracted from image (low level vision) and before object recognition and scene understanding (high level vision)

Question 2

What is the goal of middle vision

Answer 2

to organize elements of visual scene into groups that we can recognize as objects

Question 3

Perceptual organization

Answer 3

the process by which elements in environment become perceptually grouped to create our perception of objects

Question 4

Name and explain the 2 components of perceptual organization

Answer 4

1. Grouping: process by which visual events are put together into units or objects
2. Segregation: process of separating one area or object from another

Question 5

Structuralism

Answer 5

approach that believes that complex objects or perceptions could be understood by analysis of components

Question 6

Why did Gestalt psychologists reject structuralism? (x2)

Answer 6

• > did not accept idea that perceptions were formed by “adding up” sensation
• > did not accept that past experience plays major role in perception

Question 7

Name 2 demonstrations that oppose structuralists

Answer 7

1. Apparent movement

2. Illusory contours

Question 8

Discuss the apparent movement principle

Answer 8

principle behind illusion of movement created by stroboscope, in which nothing is actually moving, although movement is perceived

• > 2 images flashing on/off separated by period of darkness which is not seen because our perceptual system adds perception of image moving through space between flashing image
• > whole is different than sum of its parts

Question 9

Discuss illusory contours

Answer 9

contour that is perceived even though nothing changes from one side of it to the other in an image

• > edges create triangle despite no physical edges being present
• > cannot be created y sensations
• > whole is different than sum of its parts

Question 10

How do the Gestalt principles act like committees?

Answer 10

some overrule, some don’t

Question 11

Discuss law of pragnanz/good figure/simplicity

Answer 11

every stimulus pattern is seen in such a way that the resulting structure is as simple as possible e.g. olympic symbol

Question 12

Discuss law of similarity

Answer 12

similar things appear to be grouped together due to colour, shape or orientation

Question 13

Discuss law of good continuation

Answer 13

points that when connected result in straight or smoothly curving lines are seen as belonging together and the lines tend to be seen in such a way as to follow the smoothest path

Question 14

Discuss law of proximity

Answer 14

things near each other appear to be grouped together

Question 15

Discuss principle of common region

Answer 15

elements that are within the same region of space appear to be grouped together

Question 16

What does the principle of common region override?

Answer 16

law of proximity

Question 17

Discuss the principle of uniform connectedness

Answer 17

connected region of visual properties e.g. lightness, colour, texture is perceived as a single unit

Question 18

Discuss the principle of common fate

Answer 18

things that are moving in same direction appear to be grouped together

Question 19

Discuss the principle of closure

Answer 19

applies when we tend to see complete figures even when part of the information is missing

Question 20

Differentiate between figure and ground

Answer 20

ground - background

figure - seperate object standing out from ground

Question 21

Define reversible figure-ground

Answer 21

patterns that can be perceived different depending on what we see as figure or ground

Question 22

Define border ownership

Answer 22

even if figure and ground share contour, border is associated with figure

Question 23

Name 4 factors determining which area is figure

Answer 23

1. area
2. symmetry
3. meaningfulness
4. roundedness

Question 24

How does area determine which area is figure?

Answer 24

lower region of a display tends to be seen as figure, there is no left-right preference

Question 25

How does symmetry determine which area is figure?

Answer 25

symmetrical areas/convex regions are seen as figures

Question 26

How does meaningfulness determine which area is figure?

Answer 26

displays that look familiar to us are more likely to be seen as figures

Question 27

How does roundedness determine which area is figure?

Answer 27

a rule for figure-ground assignment stating that if one region is entirely surronded by another, it is likely that the surronded region is the figure

Question 28

Gist of a scene

Answer 28

meaning of a scene that can be recognized after only a fraction of a second

Question 29

Global image features

Answer 29

information used by us, that can be perceived rapidly and is associated with specific types of scenes, contains info on scene’s structure and spatial layout

Question 30

Name 5 global image features

Answer 30

1. degree of naturalness
2. degree of openness
3. degree of roughness
4. degree of expansion
5. colour

Question 31

Discuss how degree of naturalness is a global image feature

Answer 31

– Natural scenes (= ocean) have undulating contours while man-made scenes (= street) have straight lines, like horizontals and verticals

Question 32

Discuss how degree of openness is a global image feature

Answer 32

Open scenes (= ocean, street less) have visible horizon line and few objects, while scenes with low degree of openness (= forest) do not.

Question 33

Discuss how degree of roughness is a global image feature

Answer 33

Low roughness scenes (= ocean) have few small elements, while high roughness ones (= forest) have small and complex elements

Question 34

Discuss how degree of expansion is a global image feature

Answer 34

High degree of expansion means that there is convergence of parallel lines (think about railroad tracks in distance).

-> dependent on observer’s viewpoint

Question 35

Discuss how colour is a global image feature

Answer 35

scenes have characteristic colours, ocean scene is blue, forest green/brown etc

Question 36

Regularities in environment

a) define
b) name 2

Answer 36

a) Characteristics of environment that occur frequently, such as landscapes are often green and smooth, and verticals and horizontals are associated with buildings.
b) physical and semantic

Question 37

Physical regularities

Answer 37

regularly occurring physical properties of the environment

• > more verticals+horizontals in environment than oblique explaining oblique effect
• > objects have homogenous colours

Question 38

Light-from-above assumption

Answer 38

– Assumption that light is coming from above. Made because most light in our environment actually comes from above.

Question 39

Semantic regularities

Answer 39

Characteristics associated with functions carried out in different types of scenes.

-> meaning of a scene

Question 40

How do people infer what is present in a scene?

Answer 40

use physical and semantic regularities

Question 41

Discuss retinal ambiguity in relation to Helmholtz

Answer 41

particular pattern of stimulation on retina that can be caused by many different possible objects in environment

Question 42

Discuss theory of unconscious inference in relation to Helmholtz

Answer 42

some of our perceptions are the result of unconscious assumptions we make about the environment.

Question 43

Discuss the likelihood principle in relation to theory of unconscious inference

Answer 43

we perceive object that is most likely to have caused pattern of stimuli we have received

Question 44

Nonaccidental feature

Answer 44

of an object is not dependent on the exact viewing position of the observer when occluded

Question 45

Global superiority effect

Answer 45

the finding in various experiments that the properties of the whole object take precendence over the properites of parts of the object

Question 46

Bayesian inference

Answer 46

Way of formalizing idea that our perception is combination of current stimulus and our knowledge about conditions of the world – what is and is not likely to occur.

->  Statistical technique that enables us to calculate the probability (P) that the world is in a particular state (A) given a particular observation (O).

Question 47

Link the visual areas associated with each level of vision and describe

Answer 47

V1 – Low-level vision – Cells respond best to lines and edges in specific areas of visual field.

V2 – Middle-level vision – Cells have sensitivity to border ownership and illusory contours.

V4 – High-level vision – Cells are more interested in complex attributes. No perfect stimuli have been found for this area, but warmer and darker colors generate more response, as well as stimuli with feature pointing to the right.

Question 48

The ___ the response the more likely someone can identify something

Answer 48

larger

Question 49

Binocular rivalry

Answer 49

if each eyes receives totally different images, the brain can’t fuse the 2 images therefore the observer perceives either the left-eye image or right-eye image (but not both at the same time)

Question 50

Naive template theory

Answer 50

Proposal that visual system recognizes objects by matching the neural representation of the image, with a stored representation of the same ‘shape’ in the brain.

Question 51

Discuss lock and key in relation to the naive template theory

Answer 51

Stimulus has to fall on array of spot detectors. If it falls on filled detectors and not empty ones, it is identified.

Question 52

Recognition-by-components model

Answer 52

Biederman’s model of object recognition which holds that object’s are recognized by identities and relationships of their component parts (based on Gestalt principles: symmetry, parallelism etc)

Question 53

Geon

Answer 53

Any of the ‘geometric ions’ out of which perceptual objects are built.

Question 54

Viewpoint invariant

Answer 54

Property of object proposing that representations of object do not change when observer viewpoint changes.

Question 55

Entry-level category

• subordinate level
• superordinate level

Answer 55

For object, label that comes to mind most quickly when we identify it (= bird).

• Subordinate level – Object might be more specifically named (= eagle).
• Superordinate level – Object might be more generally named (= animal).

Question 56

Pure alexia

Answer 56

inability to recognize a single word, faces, objects, digits, numerals - can speak and even write

Question 57

Neuronal recycling hypothesis

Answer 57

– Human brain contains highly organized cortical maps that constrain subsequent learning.

Question 58

Where do illusory contours evoke response?

Answer 58

area 18 of VC (V2)

Question 59

Population coding

Answer 59

information about the outside world and plans for motor action are represented by the firing patterns of neurons – temporal sequences of action potentials, also known as spikes

Question 60

Population codes

Answer 60

are neural representations at the level of groups of cells.