object recognition

Question 1

what is object recognition

Answer 1

perception of familiar items (memory)

Question 2

why is object recognition so difficult

Answer 2

environments contain hundreds of overlapping objects

yet perceptual experience is of structured, coherent object which we can recognise, use and usually name

apparent size and shape of object does not change despite large variations in retinal image
-our understanding of the object doesn’t change

Question 3

examples of object variability

Answer 3

translation invariance
rotation invariance
size invariance (could be bigger/smaller or closer/further)
colour
partial occlusion and presence of other objects

Question 4

intra-class variation

Answer 4

all chairs vary widely, but we still know that they are all chairs

we can recognise them when only part of an object is visible

Question 5

viewpoint variation

Answer 5

we can recognise an object from many different view points

objects may be easier to recognise from some view points

Question 6

template theory

Answer 6

mini copy or template in long term memory of all known patterns

multiple templates are held in memory

compare stimuli to templates in memory for one with greatest overlap until a match is found

good match to template = recognition

Question 7

questions about template theory

Answer 7

normalisation?
numerous templates?
what type of template?
how does this work for complex patterns?
how good a match is good enough?
what if an object has no template match?

Question 8

critique of the template theory

Answer 8

problem of imperfect matches
cannot account for the flexibility of pattern recognition system
comparison requires identical orientation, size, position of template to stimuli

Question 9

prototype theories

Answer 9

modification of the template matching theory (flexible templates)

possess average of each individual characteristic (prototype)

no match is perfect; a criterion for matching is needed

Question 10

Frank and Bransford 1971

Answer 10

evidence for the prototype theory

presented items based on prototypes
prototype not shown
yet participants were confident that they had seen the prototype
suggests the existence of prototypes

however prototypes cannot account for all objects/ patterns

Question 11

feature theories

Answer 11

pattern consists of a set of features or attributes
need to know the relationship between features

Question 12

structural distribution

Answer 12

describe the nature of components of a configuration and the structural arrangement of these parts

Question 13

2D pattern matching theories

Answer 13

template theories
prototype theories
feature theories
structural description

Question 14

basics steps of 3D object recognition

Answer 14

early image processing: must first interpret input to the visual system as coherent structures, segregates from one another and from the background

then must be processes to give a description- which can then be matched to the descriptions of visual objects stored in memory

Question 15

three questions for object recognition

Answer 15

what elements are used in the description? (primitives)

how is the relationship between these elements specified?

how is the overall description invariant across views?

Question 16

Marr and Nishihara (1978)

Answer 16

objects are made of cylinders, must specify relationship between cylinders to give a structural description

expressed structural relations by a hierarchal organisation of cylinders

each cylinder has and axis and way in which other are joined are expressed as coordinates

the description of each cylinder is describes relative to its own axis, resulting in a description which is invariant across viewpoints

Question 17

Biederman (1987, 1989) recognition by components theory

Answer 17

objects comprised of basic shapes

geons = geometrical ions
-blocks, cylinders, arcs, wedges
-approximately 36 different voluntary shapes
-viewpoint invariant theory

relationship between geoms allows for object identification

small number of structural relationships

concave parts of an objects contour helpful in segmenting visual image into parts

geons specified in terms of ‘non-accidental’ properties

regularities in the visual image thought to reflect actual (non-accidental) regularities in the world

according to model, forms of degradation which disrupts the basis for identifying geons should make the object more difficult to recognise

Question 18

Biederman structural relationships

Answer 18

relative size
verticality
centring
relative size of surfaces at joint

Question 19

non-accidental properties of geons

Answer 19

curvature - points on a curve

parallel - set of points in parallel

co-termination - edges terminating in a common point

symmetry - versus asymmetry

co-linearity - points in a straight line

Question 20

biederman (1987)

Answer 20

slow an inaccurate at ‘non recognisable’ stimulus, but relatively good at recognisable

points of concavity more easy to recognise

deletion of component affects matching stage - reducing the number of components to match to
-at brief exposures (65ms) partial objects better recognised

midsegment deletion makes it more difficult to determine components
-at longer exposures (200ms) midsegment deletion led to less errors

Question 21

biederman support

Answer 21

vogels, biederman, bar and Lorincz (2001) found some cortical neurons in monkeys sensitive to geons

assessed the response of neurons in the inferior temporal cortex to change in geon or change in size of object

some neurons responded more to geon changes, providing support for geons

Question 22

evaluation of biederman

Answer 22

flexible and comprehensive system for describing objects, but why 36 geons?

experimental results consistent with model but doesn’t provide a critical test

doesn’t explain how descriptions are matches to those stored (how does object recognition occur?)

Question 23

advantages of biederman

Answer 23

recognises the importance of the arrangements of the parts

parsimonious: small set of primitive shapes
-structural description of relationships emphasised

Question 24

disadvantages of biederman

Answer 24

structure is not always the key to recognition
-texture not considered

which geons?

doesnt account for within category discrimination

de-emphasises the role played by context in object recognition

simplifies the contribution of viewpoint-dependence
-doesn’t explain why viewpoint may affect ease of recognition

Question 25

viewpoint dependent theory

Answer 25

assume that changes in viewpoint reduce the speed and/or accuracy of object recognition

evidence suggests sometime viewpoint invariant mechanisms are used, and other times viewpoint dependent mechanisms are used

viewpoint dependent mechanisms are more important for within category discriminations

Question 26

vanrie et al. (2002)

Answer 26

viewpoint dependent = complex within category decisions

viewpoint invariant = easy categorical decisions

Question 27

Tarr and Hayward (2018)

Answer 27

object representations are neither viewpoint-dependent nor viewpoint-invariant

Question 28

issues with object recognition theories

Answer 28

any theory of object recognition must address the binding problem = how do we integrate different kinds of information to produce object recognition?

when presented with several objects how do we decide which features belong to which objects?

Question 29

beyond recognition

Answer 29

once a structural description of an object is formed, it must be matched to stored representations

if there is a match then object is ‘recognised’

Question 30

evaluation Humphreys et al 1988

Answer 30

oversimplification? - as later processes may start before earlier ones have been completed? stages more integrated?

general support for model from patients with object recognition difficulties - associative agnosia