6. The seeing brain

Question 1

what is the main visual route in the brain called?

Answer 1

geniculostriate pathway

> goes via the lateral geniculate nucleus LGN

> terminates in striate cortex

Question 2

how many layers does LGN have?

Answer 2

LGN

> 6 layers, 3 for each eye

Question 3

damage to parts of V1 result in?

Answer 3

blindness for the corresponding region of space

> e.g. hemianopia

this is due to retinotopic organization of V1

Question 4

which brain area responsible for percieving

colour?

movement?

Answer 4

colour: V4
movement: V5/MT

Question 5

why do we need area V4?

what happens when V4 is damaged?

Answer 5

Area V4 is responsible for colour constancy, that is computing the colour of an object taking the lighting conditions in account

> damage leads to achromatopsia, the loss of colourvision

Question 6

what happens with patients with (bilateral) damage to V5?

what is not impaired?

Answer 6

those patients suffer of akinetopsia, they dont percieve movement

> see the world in a series of still frames

> however they still can percieve movement via the other senses

Question 7

what are the 4 broad stages of object recognition?

Answer 7

object recognition

1. early visual processing (features)
2. grouping of visual elements (gestalt)
3. matching grouped visual description to representation of object stored in brain
4. attaching meaning to the object

Question 8

4 grouping rules in figure-ground segregation

Answer 8

1. proximity
2. similarity
3. good continuation
4. closure

Question 9

what are disorders in object recognition called?

Answer 9

agnosia

Question 10

what are the two different types of agnosia?

Answer 10

1. apperceptive agnosia - disorder of perception
2. associative agnosia - disorder of meaning

Question 11

what is integrative agnosia?

Answer 11

integrative agnosia is a form of apperceptive agnosia where the grouping principles are disrupted

Question 12

what are the two types of fotoreceptors in the retina?

what are they for?

Answer 12

cones: percieve colour, need more light
rods: not colour sensitive, more sensitive to low lights, night vision

Question 13

what is effective neural coding?

example?

Answer 13

effective neural coding: only a small number of neurons need to be active to represent a particular visual stimulus

example: lateral inhibition, only the neurons representing the edges and contrasts of a visual stimulus have to be active to percieve the whole stimulus

Question 14

what is the function of the lateral occipital complex?

Answer 14

LOC:

> generally involvend in object recognition

> prefers intact shapes

Question 15

what is blindsight?

caused by damage where`?

Answer 15

blindsight: no conscious visual perception of stimulus, but abled to make forced choice discrimination above chance level

caused by damge to V1

Question 16

what is visual neglect?

caused by damage where?

Answer 16

visual neglect: patients do not respond to stimuli in one hemifield

> however when instructed where stimulus is, they can interact with it

> neglect more a deficit of attention than of vision

caused by damge to the posterior parietal lobe

Question 17

what is multistable perception?

Answer 17

perception of an ambiguous stimulus alters between different interpretations