vision 2

Question 1

what is lateral inhibition

Answer 1

• object detection
  in each eye the axons are connected in a lateral inhibitory neural network.

When light hits the ommatidia they fire at a rate proportional to the intensity of the light.

The more they fire the more they inhibit their neighboours via lateral inhibition

This means that at points of contrasting illumination the difference is exaggerated

occurs only at the edge- amplifies relative difference.

Horizontal cells responsible: They reverse the sign of their input.

Question 2

The Hermann Gridd

Answer 2

grey blobs at the intersection disappear when they are foveated.
- consequence of lateral inhibition- The intersection is surrounded by more activated receptive fields.

Question 3

Mach bands

Answer 3

The apparent change in brightness between bands is an illusion caused by lateral inhibition
Mediated by horizontal cells which when activated inhibt the other cells they are in contact with
For example in an on- centre off surround cell the horizontal cells inhibit the outside which causes the difference to be amplified.

Question 4

Projection to the brainstem accessory optic and pre tectal nuclei

Answer 4

responsible for visual reflexes such as accommodation, vergence, pupillary control

• shining a light in one eye will result in reflex pupil control in both eyes.

Question 5

Retino- tectal pathway: projections to the superior colliculus

Answer 5

GAZE shift- foveation

• projects contralaterally
• seperate at the optic chiasm.

Properties of the colliculus initiates gaze shifting.

Question 6

retino- geniculate- striate pathway

Answer 6

scene analysis and object identification

• takes visual information from the retina to the lower layer of the primary visual cortex (V1) via the lateral geniculate nuclei of the thalamus.
• Retinotopic mapping
• The retino- geniculate striate system is retinotopic: each relay is orgorganised according to a spatial map of the retina.

Question 7

Projections

Temporal hemiretina - Nasal hemiretina

Answer 7

Temporal hemiretina (ipsilaterally) 
Nasal hemiretina (contralaterally)

Question 8

binocular overlap

Answer 8

allows for depth perception

Question 9

the lateral geniculate nucleus : The thalamic relay

Answer 9

P and M layers

P layers: Small cell bodies , responsive to colour, fine detail - scene analysis and object identifcation: CONES

M layers: Large cell bodies, luminance change- on/off, movement. RODS provide input (Similar to superior colliculus)

Question 10

Receptive fields

Answer 10

The receptive field of a visual neuron is the area in which it is possible to influence the firing of that neuron.

• increase or decrease.

Question 11

Hubel and Weisel

Answer 11

Recorded the three levels of the retina-geniculate-striate system:

1. retinal ganglion cells
2. lateral geniculate neurons
3. striate neurons of lower layer IV

Four commonalities

1. Receptive fields in the foveal area of the retina were smaller than those at the periphery
2. All had circular receptive fields
3. All neurons were monocular (had a receptive field in one eye but not the other)
4. Had receptive fields that comprised an excitatory area and an inhibitory area separated by a circular boundary

Question 12

Simple cortical cells (v1)

Answer 12

• Simple cells have antagonistic on/ off regions
• borders are straight rather than circular
• respond best to bars of light in specific orientations at a specific location in the visual field

Question 13

complex cells

Answer 13

more common
do not have static on off regions, they respond best to particular straight edge stimulus of a particular orientation regardless of its position within the receptive field

Question 14

columnar organisation

Answer 14

flow from on/ off cells to simple cells to complex cells
All simple and complex cells in a column prefer straight line stimuli in the same orientation

Complex receptive field properties required for scene analysis.

Question 15

horizontal electrode track

Answer 15

if you move an electrode along a horizontal track the spatial location of the receptive fields shift systematically
the preferred orientation of the neurons at the tip shift.

Question 16

v2

Answer 16

similar to V1 but for complex shape characteristics

Question 17

V3

Answer 17

form, motion, depth

Question 18

V4

Answer 18

colour, form, stimulus saliency, attention

Question 19

V5

Answer 19

motion

Question 20

The ventral stream

Answer 20

Travels to the temporal lobe- scene analysis: WHAT

Question 21

the dorsal stream

Answer 21

travels to the parietal lobe- spatial locations

WHERE

Question 22

blindsight

Answer 22

normally the retino- tectal and retino- geniculate-striate systems operate together, BUT brain damage = consciously blind but retain visual abilities/ awareness

• mediated by the remaining functionality of the subcortical visual system (Colliculus) which can communicate directly with other cortical areas in the absence of cortical input

Question 23

visual neglect

Answer 23

unaware of the existence of a particular part of their visuall field.

Question 24

visual agnosia

Answer 24

see an object but unable to attribute meaning to it

Question 25

Visual agnosia - prospagnosia

Answer 25

inability to identify faces - even family members

Question 26

luminance change

Answer 26

movement detection