Problem 5 - DONE

Question 1

levels of vision

Answer 1

• low-level vision = extraction of basic features from image
• -> V1 (sensitivity to lines/edges in specific locations)
• middle-level vision = organisation into groups of elements of visual scene
• -> V2 (sensitivity to border ownership, real and illusory contours)
• high-level vision = object recognition and scene understanding
• -> V4 (interest in complex attributes)

Question 2

perceptual organisation

Answer 2

= process by which elements in environment become perceptually grouped
- goal: create perception of objects
two components:
- grouping = visual events are put together into units/objects
- segregation = separating one area/object from another

Question 3

structuralism

Answer 3

= distinguished between sensations and perceptions

• -> sensations = elementary processes; occur due to stimulation of the senses
• -> perceptions = more complex, conscious experiences; e.g. our awareness of objects

=> rejected by Gestalt psychology

• apparent movement
• illusory contours

Question 4

Gestalt psychology

Answer 4

= roughly translated, means configuration

- how are configurations formed from smaller elements?

Question 5

apparent movement

Answer 5

= illusion of movement; although movement is perceived, nothing is actually moving
- physically: two images flashing on/off, separated by period of darkness
–> perceptually: don’t see darkness, because perceptual system adds during period of darkness (connects both pictures)
- demonstration against structuralism
–> there are no sensations in the dark space between the flashing images
=> the whole is different than the sum of its parts

Question 6

illusory contours

Answer 6

= illusion of contour; although contour is perceived (edges create triangle), there actually are no physical edges present
- demonstration against structuralism
–> there are no sensations along contours, there is only white between
=> the whole is different than the sum of its parts

Question 7

gestalt organising principles

Answer 7

• determine how elements in a scene can become grouped together
• connect bottom-up processing (elements that occur in environment) with top-down processing (our knowledge/memory what usually belongs together)
• heuristics ≠ laws
• -> likelihood principle = we perceive the object that is most likely to have caused the pattern of stimuli we have received

Question 8

principle of good continuation

Answer 8

= 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

• example: objects that are partially covered by other objects are seen as continuing behind the covering object
• also in auditory perception

Question 9

principle of prägnanz/good figure

Answer 9

= every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
- example: olympic signal (see it as five circles and not as a larger number of more complicated shapes)

Question 10

principle of similarity

Answer 10

= similar things appear to be grouped together

• -> colour, shape, size, orientation
• also in auditory perception

Question 11

principle of proximity/nearness

Answer 11

= things that are near each other appear to be grouped together

Question 12

principle of common fate

Answer 12

= things that are moving the same direction appear to be grouped together
- even if objects are dissimilar

Question 13

principle of common region

Answer 13

= elements that are within same region of space appear to be grouped together
- example circles within ovals: overpowers proximity (proximity: nearby circles would be perceived together; common region: circles do not group, we perceive circles inside ovals as belonging together)

Question 14

principle of uniform connectedness

Answer 14

= connected region of the same visual properties is perceived as a single unit
–> same visual properties: lightness, colour, texture, motion

Question 15

perceptual segregation

Answer 15

= perceptual separation of one objet from another

• determine properties of figure and ground
• determine what causes us to perceive one area as figure and other as ground
• -> problem of figure-ground segregation

Question 16

problem of figure-ground segregation

Answer 16

• figure = when we see separate object; figure that stands out from its background
• -> more thing-like, memorable, seems to in front
• -> border ownership
• ground = background
• -> not memorable
• -> near borders: unformed material, without specific shape

Question 17

reversible figure-ground

Answer 17

= patterns that can be perceived different/alternately depending on what we see as figure/ground

Question 18

what factors determine which area is figure?

Answer 18

• area: lower region of a display
• -> no left-right preference
• symmetry: symmetrical areas/convex regions
• meaningfulness: displays that look familiar to us
• grouping

Question 19

inference in perception

Answer 19

= use knowledge of physical and semantic regularities to infer what is present in a scene

• retinal ambiguity = pattern of stimulation on retina that can be caused by many different objects
• theory of unconscious inference = some perceptions are the result of unconscious assumptions we make about the environment
• -> likelihood principle

Question 20

bayesian inference

Answer 20

= perception is combination of current stimulus and our knowledge about conditions of the world
–> what is and is not likely to occur
- statistical technique to quantify inferential perception
–> enables to calculate probability that world is in a particular state given a particular observation
two factors:
- prior probability (likelihood of outcome we are proposing)
- consistency of hypothesis with each outcome

Question 21

object recognition

Answer 21

• what pathway/ventral stream
• several difficulties of environment are easily solved by humans:
• -> inverse projection problem
• -> viewpoint invariance

Question 22

inverse projection problem

Answer 22

= determining the object responsible for a particular image on the retina
- starting with image on retina –> extending rays out from eye

Question 23

viewpoint invariance

Answer 23

= ability to recognise an object seen from different points of view
–> enables to tell whether faces seen from different angles are the same

Question 24

theories of object recognition

Answer 24

• naive template theory

- recognition-by-components model

Question 25

naive template theory (image descriptions)

Answer 25

= visual system recognises objects by matching the neural representation of the image (low-level features) with a stored representation in memory (template)

• problem: one would need way too many templates
• solution: conceptual match (instead of matching each point to one template)
• -> matching of structural descriptions = description of an object in terms of the basic nature of its parts and the relationship between those parts

Question 26

recognition-by-components model (structural descriptions)

Answer 26

= objects are recognised by identities and relationships of their component parts

• we have a library of basic shapes/geons in our brain
• -> geons (“geometric icons”) = basic set of 3D shapes
• collection of non-accidental features (viewpoint invariance) –> robust to noise/orientation
• problems:
• -> object perception is not completely viewpoint invariant (letter recognition is object dependent) + cannot distinguish objects that differ in detail (naive template theory)
• -> cannot explain language of object recognition
• two objects can have exactly the same structural description/ visual representation but a different name

Question 27

levels of object recognition

Answer 27

• entry-level category = label that comes to mind most quickly when we identify it (e.g. bird)
• subordinate level = the object might be more specifically named (e.g. eagle)
• superordinate level = it might be more generally named (e.g. animal)

Question 28

un-learn viewpoint invariance

Answer 28

• has to be suppressed to learn reading letters
• letters do not stay the same from every point of view (b and d)
• visual word form area: suppresses viewpoint invariance for letter recognition