Visual Processing of the brain

Question 1

Primary visual cortex

Answer 1

-Majority of ganglion cell axons go back to primary visual cortex (via LGN)
-Contralateral Arrangement= the left visual field signals are processed in the right hemisphere and vice versa
N.B- Damage to area V1 can occur after a stroke affecting the posterior cerebral artery  neurons supplied by this artery are starved of nutrients and are damaged

Question 2

Retinotopic organisation

Answer 2

-Cells closer together get input from same region of the retina
 Upper bank of calcarine sulcus in the occipital lobe has neural responses to light stimulation in lower half of visual field
 Lower bank of calcarine to upper half of visual field

Question 3

Cortical magnification

Answer 3

-More cells from processing information in the fovea and progressively fewer cells to process signal coming from the periphery

Question 4

Functional organisation of V1

Answer 4

Visual Cortex
-6 layers of neurons with visible anatomical differences
Cortical column modules
-Process information in small region of space (a column for each location in space)
Blob regions
-Cells respond to colour variation
-Interblob regions: orientation, motion, depth

Question 5

Specialised areas in V1

Answer 5

1) Primary visual cortex (also known as the first visual area, or V1)
2) Area V4, which has neurons that are sensitive to the colour of visual inputs
3) Area MT, which is responsive to moving visual stimuli
4) Inferior temporal cortex, which contains neurons that are selectively responsive to complex objects and faces

Question 6

Two-stream hypothesis

Answer 6

-Ventral stream computes a detailed map of the world from visual input
-Dorsal stream transforms incoming visual information for action/ location

Question 7

Colour processing pathway

Answer 7

-Area V4 is highly responsive to colour
-Achromatopsia is selective loss of colour perception/ damage to one hemisphere results in achromatopsia in contralateral visual field

Question 8

Motion processing pathway

Answer 8

-Cells in V1 are orientation selective (respond to moving bars or edges with specific orientation)
MT neurones influence perception of movement
-Area V5 of extrastriate cortex (also known as MT) contains neurons that respond to movement/ damage to this region severely disrupts ability to perceive moving stimuli
MST integrates local motion
-MST area contains neurons that are sensitive to optic flow, responsive to complex movement, associated with the perception of biological motion

Question 9

The computational theory

Answer 9

The computational theory
Find the image contours (the basis of shape)
Find the contours that reflect the structure of objects
edges
lines
curves
The algorithm
Look for changes in the retinal image - edges
Look for changes that form a straight line
Look for lines that form a curve
The implementation
Some physiological evidence (especially the early stages)
Edges - LGN
Lines – V1
Curves - V4

Question 10

Inferior temporal cortex

Answer 10

-Assuming hierarchical processing, is known as the ‘what’ pathway
-Synthesis to form, colour an depth
-Large receptive fields when an object moves, changes in size

Question 11

damage to V1 causes a loss of visual awareness

Answer 11

-Loss of conscious awareness of a visual scene when there is total bilateral destruction of V1 (unconscious processing still remains)
-Small unilateral lesion of V1 will lead to scotoma
-Homonymous hemianopia= unilateral destruction of V1 in its entirety will cause blindness in the whole of the contralateral visual field

Question 12

Blindsight

Answer 12

preserved visual capacities in the absence of conscious visual experience e.g- pupillary reflexes, orientation and shape discrimination

Question 13

Why are we only aware of a small part of our visual world

Answer 13

-Neural limitations  bottleneck of the optic nerve
-Metabolic limitations  neural activity requires a lot of energy and blood oxygenation
-Computational efficiency  assign most neural machinery to processing important objects
-Conscious decision making

Question 14

Place cells in the hippocampus

Answer 14

-Cells fire at specific real world locations
-Hippocampus provided neural instantiation of a spatial map

Question 15

Grid cells, head direction cells, border/ boundary cells

Answer 15

Grid cells
-Medial entorhinal cortex
-Fire in a regular hexagonal lattice of locations tiling the floor of the environment
Head directional cells
-Fire on the basis of the direction the head is facing
Boarder/ boundary cells
-Fire when the animal is set distances from navigational boundaries facing in specific directions

Question 16

Parahippocampal place area (PPA)

Answer 16

-region in the visual cortex that preferentially processes scenes (e.g- landscapes, cityscapes, rooms etc.)
-PPA is sensitive to the global spatial geometry/ configuration of scenes
-PPA’s response is highest to scenes that depict realistic spatial layout/ lower if position of objects in the scene are scrambled