pattern perception

Question 1

are visual pathways heirarchial?

Answer 1

yes

Question 2

how are image estimates transformed into known objects?

Answer 2

there is a sequence of processing required

Question 3

what happens in the heirarchial processing sequence?

Answer 3

at each local patch in the image we extract info then spatial frequency tuned channels carry the signal through the early stages

Question 4

what visual pathway is responsible for pattern and object perception?

Answer 4

the ventral cortical visual pathway

Question 5

what are the two tests to object recognition?

Answer 5

• detection of local features (find edges)

- grouping of elements to make bigger clusters

Question 6

how do we find edges?

Answer 6

V1 receptive fields localise points so they can find the edges

Question 7

what is an issue with finding edges?

Answer 7

it gives us too many lines and they arent always connected around the border

Question 8

how is finding edges improved?

Answer 8

looking for edges that coincide in different spatial frequency ranges but still need to group appropriate segments together

Question 9

what does grouping involve?

Answer 9

contours tend to be smooth in local regions so elements that extend a contour with minimal change in orientation are likely to be the same colour

Question 10

what are the gestalt grouping principles?

Answer 10

No grouping
Proximity
Similarity of colour 
Similarity of size
Similarity of orientation
Common motion 
Symmetry
Parallelism

Question 11

what do contours mark?

Answer 11

object boundaries which allows recognition

Question 12

what needs to happen with objects overlap?

Answer 12

need to segment contours into objects so we used matched concavities in the profile as the point where objects are segmented

Question 13

does primary knowledge have an impact on how we interpret a scene and how?

Answer 13

yes, contours are ambiguous so we use our prior knowledge to determine the most likely cause of the image

Question 14

what is the bayesian analysis formalised expectation?

Answer 14

the probability of a stimulus given the image that we are seeing ie. the probability that what we think the image is is what it actually is

Question 15

what are some ideas around the bayesian expectation formula?

Answer 15

• can potentially explain some illusions
• adaption can change expectations
• expectations often hard to accurately specify

Question 16

what is the consequence of cortical damage in the mid level pattern processing pathways?

Answer 16

cortical damage in the V1 leads to scotoma which can cause problems with grouping

Question 17

how is autism effected by the existence of mid level perceptual losses?

Answer 17

• focus better on parts of complex stimulus
• weak central coherence theory
• better embedded figures test performance
• motion: poorer global motion thresholds

Question 18

how are migraines effected by the existence of mid level perceptual losses?

Answer 18

visual aura symptoms and dysfunction in both the M and P pathways

Question 19

what is apperceptive agnosia characterised by?

Answer 19

cannot name, match or discriminate visually presented objects, despite adequate elementary visual function

Question 20

what is the deficit in apperceptive agnosia?

Answer 20

involves an inability to process features, such that they are not fully available for developing a percept of the overall structure of an object

Question 21

what does a CT show in someone with apperceptive agnosia?

Answer 21

CT showed hypo densities in both occipital loves and minor one in right parietal lobe

Question 22

what is associative agnosia?

Answer 22

cannot use the derived representation to access stored knowledge of the objects functions and associations

Question 23

what does a CT show in someone with associative agnosia?

Answer 23

bilateral thinning on MRI in occipitotemporal region but no clear lesion

Question 24

what is an example for someone with associative agnosia?

Answer 24

is able to copy and match the drawing even though unable to identify it

Question 25

what is integrative agnosia?

Answer 25

appears to over-segment and identify objects piecemeal and

cannot exploit Gestalt grouping principles