Primary visual cortex and beyond

Question 1

which retinogeniculate pathway would be required to resolve the highest spatial frequencies?

Answer 1

-

Question 2

magno- and parvocellular response properties

Answer 2

see graph

Question 3

what is segregation of M and P pathways partially maintained by?

Answer 3

V1

Question 4

modular hypothesis of visual function

Answer 4

-functional specialisation of visual cortex
-parallel and separate processing of image attributes in different cortical areas
1. colour
2. form
3. motion

Question 5

origin of parvocellular

Answer 5

midget ganglion cells

Question 6

origin of magnocellular

Answer 6

parasol ganglion cells

Question 7

where are P and M cells found?

Answer 7

LGN

Question 8

what is ventral/temporal pathway?

Answer 8

parvocellular

Question 9

what is dorsal/parallel pathway?

Answer 9

magnocellular

Question 10

anatomy of visual areas

Answer 10

V1 -> V2 -> V3 -> MT or V4
MT (dorsal pathway) -> parietal cortex (7a, STP, VIP, LIP, MST)
V4 (ventral pathway) -> Temporal cortex ( TEO -> TE)

Question 11

what is the function of the dorsal pathway?

Answer 11

spatial vision function

Question 12

what is the function of the ventral pathway?

Answer 12

object recognition

Question 13

what is evidence for the the distinct visual pathways d and v stream?

Answer 13

-lesion experiments in trained monkeys
-double dissociation between recognition and location

Question 14

suggest evidence for functional specialisation

Answer 14

• lesion studies
• neurophysiological assessment following focal brain damage in humans
• electrophysiology
• imaging

Question 15

discuss the complex visual responses in inferotemporal cortex (IT)

Answer 15

-from 1970s reports of cells from monkey visual association cortex responsive to complex stimuli such as hands or faces (‘face cells’)
-skepticism?

Question 16

state the properties of neurons in inferotemporal cortex

Answer 16

• Large RFs, sometimes extending across midline, usually including fovea
• response invariant: retinal size and precise position within RF doesn’t affect response
• many cells are ‘face cells’ (well establishment now) but other patterns can be effective and may be modifiable with training, attention etc.

Question 17

state the neuron doctrine

Answer 17

• Barlow 1972
• Neural responses become increasingly selective at higher stages in neural pathways
• specific elements of our perceptions are caused by activation of specific populations of neurons, selective for those elements
  
  • termed cardinal cells or grandmother cells
  • implies population size must decrease as selectively increases: sparse coding

Question 18

state the functions of motion in the visual stimulus

Answer 18

• draws attention
• helps figure-ground segregation
• location and navigation

Question 19

describe detection of motion

Answer 19

-detectors with delay line; Reichardt model (delay gives direction sensitivity)
-illusions of visual motion also suggestive of specialised motions-processing subsystem
-waterful illusion or motion after-effect

Question 20

expand on area MT (V5) and motion processing

Answer 20

-receives input from M-pathway via V1 and V2
-retinotopically mapped
-cells sensitive to direction and speed of motion
-columnar organisation

Question 21

what are many V1 cells sensitive to?

Answer 21

motion, perpendicular to orientation axis

Question 22

is MT necessary for motion perception

Answer 22

-lesion studies; monkeys impaired on motion discrimination taks
-case LM

Question 23

global vs elemental visual motion

Answer 23

-some V1 cells are sensitive to moving oriented edge - why do we need a separate area for motion perception?
-consider aperture problem - could V1 cells code global motion direction?

Question 24

describe plaid gratings and motion

Answer 24

-elemental motion components are the direction of each grating
-superimposed there is a global motion component
-many cells in area MT respond to global motion; all in V1 respond to elemental