Visual system

Question 1

Explain how you go from looking at an image to registering this in the brain?

Answer 1

1. The right visual hemisphere is projected to the left hemisphere and vice versa, so the left side of an image is projected to the right side of each retina of the eyes
2. The information is carried through the optic nerves from both halves of the visual field
3. At the point of the optic chiasm, the information splits from each eye, so that all of the left visual field is projected to the right hemisphere and the same for the right part of the visual field, it is projected to the left hemisphere
4. The next step along the route is the lateral geniculate nucleus, this is the thalamic relay system within the visual system
5. Information is then projected through optic radiations in the white matter to the primary visual cortex (Brodmann area 17 AKA Calcarine cortex AKA V1, in the occipital lobe) and then throughout other visual areas of the brain

Question 2

How does a lesion at the optic chiasm present?

Answer 2

Bitemporal hemianopia
- This is where the lateral visual field is affected in both eyes but on opposite HEMI fields but the nasal/medial part of the visual field is intact in both eyes

Question 3

How does a lesion in the optic tract present?

Answer 3

Homonymous hemianopia

• This is a field defect involving either two right or left halves of the visual fields of both eyes
• So, you will get let visual field loss in both eyes etc

Question 4

How do lesions of the optic radiations present?

Answer 4

Homonymous quadrant anopia

- One/the same quadrant of the visual field is missing in both eyes

Question 5

How do lesions in the visual cortex present?

Answer 5

Homonymous hemianopia or quadrant anopia

Question 6

Patients with lesions in the V4 area have difficulty perceiving what?

Answer 6

Colour

Question 7

Patients with lesions in the V5 area have difficulty perceiving what?

Answer 7

Motion

- Akinetopsia

Question 8

The lateral geniculate nucleus contains 2 cell types, what are they?

Answer 8

Magnocellular

Parvocellular

Question 9

Patients with a posterior parietal lesion show deficits in what?

Answer 9

Processing visual spatial information

- This is called Optic ataxia AKA Bálint’s syndrome

Question 10

Patients with an infero-temporal cortex lesion may suffer from what?

Answer 10

Visual form agnosia

• This is selective impairment in recognising visually presented objects
• The man that mistook his wife for his hat