visual processing in the brain

Question 1

what does the brain want to know from visual information

Answer 1

• conscious experience of our environment involves knowing; what things are,
• the retinogeniculate pathway is largely responsible for conscious visual experience.

Question 2

visual input to the PVC

Answer 2

• majority of ganglion cell axons go back to the PVC

Question 3

contralateral arrangement

Answer 3

signals from one side of the visual field are processed by the opposite side of the brain.

Question 4

retinotopic organization of the primary visual cortex

Answer 4

• extracellular animal studies
  retinotopic organization
• cells close together get input from same region of the retina
• where an object is important for vision
• cortical magnification: more cortical cells devoted to the fovea than periphery

Question 5

functional organization of PVC

Answer 5

• visual cortex: 6 layers based on visible anatomical differences
• input to layer 2/3 and 4 from the LGN
  cortical column modules
• process information in small region of space
• but their tile the entire visual field
  blobs-
• color
  interblobs
• orientation, motion, depth

Question 6

specialized visual areas that revive input vial the PVC

Answer 6

• modular organization: each area has neurons with receptive fields that tile the visual field
  modules have slightly different function, focusing on a particular aspect of the visual scene

Question 7

hierarchal feed forward model

Answer 7

• neurons responses become more specific
• although lots of feedback and interconnection

Question 8

the two-streams hypothesis of visual processing in the brain

Answer 8

• Dorsal and ventral stream:
• the ventral stream computed a detailed map of the world from visual input
• the dorsal ‘action’ stream transforms incoming visual information for action.
• also referred to as the ‘where’ and ‘what’ pathway
• the independence of the two streams had been overemphasized.

Question 9

colour processing pathway

Answer 9

• wavelength sensitivity in the retina. speech sensitivity of L, M and S cones.
• congenital color blindness
• circulate center-surround cone opponent receptive fields in the retinal ganglion cells.
• functional segregation evident in different layers of the LGN

Question 10

R-G opponent ganglion cell

Answer 10

• excited by red light
• inhibited by green light
• (also have G-r)

Question 11

Y-B opponent ganglion cell

Answer 11

• excited by yellow light
• inhibited by blue light

Question 12

areas responsive to color

Answer 12

• area V4 is highly responsive to color, subsequent work has shown that V4 is also responsibe to changes in shape and curvature
• damage to corresponding region in human cortex causes color blindness.
• achromatopisa

Question 13

motion processing pathway

Answer 13

• retinal ganglion cells and LGN neurons respond to moving stimuli but
• stimulus could be moving in any direction
• stimulus could even just be turning off and on
• although Mangnocelluar neurons are particularly responsive to motion.
  SO cells in V1 are orientation selective: respond to moving bars or edges with specific orientation

Question 14

MT neurons influence the perception of movement

Answer 14

• the medial temporal-temporal (MT) area in the monkey has neurons with large receptive fields that are direction selective
• damage to the MT in the monkey reduces the ability to judge movement
• stimulation of individual neurons in MT biases perceived direction of motion
• motion selective neurons show adaptation.

Question 15

MST integrates local motion

Answer 15

• the media-superior-temporal (MSt) area in the monkey has neurons that are
• sensitive to optic flow (movement of the world cause by self motion)
• responsive to complex movement
• associated with the perception of biological motion.

Question 16

motion blindness (akinetopsia)

Answer 16

• caused by bilateral damage to MT (rare due to small size and location of MT)
• case of LM
• sees the world in snap shops
• unable to judge speed and therefore predict future position of moving objects
• BUT could see biological motion (so MT is not involved in perceiving structure from motion)

Question 17

types of colour blindness

Answer 17

Deuteranopia= green cones are absent or less functional
Protonopia= red cones are absent, means its difficult to distinguish between shades

Question 18

retinotopic arrangement