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Neuropsychology > Visual System Disorders > Flashcards

Visual System Disorders Flashcards

1
Q

Fill the gaps: Normal vision involves ____________ of objects and object ______________ based on size, shape, colour and past experience.

A

Localisation of objects

Object identification

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2
Q

What is the white of the eye called?

A

Sclera

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3
Q

What is the coloured part of the eye called?

A

Iris

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4
Q

What sits behind the pupil?

A

The lens

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5
Q

The opening that allows light to enter the eye and reach the retina…

A

Pupil

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6
Q

The internal lining of the rear two-thirds of the eye; converts images into electrical impulses…

A

Retina

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7
Q

The central area of the retina that is specialised for central vision (less distortion)…

A

Macula

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8
Q

The centre of the macula is the…

A

Fovea

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9
Q

Describe the optic nerve.

A

Made up of the axons of retinal ganglion cells; carries impulses for vision from the retina toward the brain.

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10
Q

How does the eyeball move?

A

Extraocular muscles enable the eye to move within its orbit.

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11
Q

Describe the flow of information in the retina.

A

At the back of the eye is the retina, which contains photoreceptor cells that convert light energy into neural activity.
Information about light flows from the photoreceptors (rods and cones) to bipolar cells to ganglion cells, which project axons out of the eye, forming the optic nerve.

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12
Q

What is the difference between the visual field and visual hemifields. For example, explain how the right hemifield is viewed.

A

The visual field is the total amount of space that can be viewed by the retina. So for one eye this is about 180 degrees.
Hemi fields are the two halves of the total visual field. For example the right nasal hemi-retina and the left temporal hemi-retina produce the right hemifield.

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13
Q

Describe the route of the ganglion axons after leaving the eye.

A

Nasal hemi retina, axons cross at the midline (chiasm).

Temporal hemi retina do not cross the midline.

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14
Q

Optic _____ –> Optic ______ –> Optic _____

A

Nerve
Chiasm
Tract

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15
Q

What would you expect if the left optic nerve was cut?

A

Vision via the left eye will be lost completely, resulting in the loss of far left peripheral vision.

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16
Q

What would you expect if there was damage to the optic chiasm?

A

Lose what nasal hemiretinas can see, so the far periphery in both hemifields.

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17
Q

What would you expect if there was damage to the left optic tract?

A

If the left optic tract is cut, vision on the right side will be lost completely (right hemianopia).

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18
Q

Where do the axons of the optic tract project to?

A

About 10% to the Superior Colliculi (in the midbrain), and the rest to the Lateral Geniculate Nuclei (in the thalamus).

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19
Q

Name the two visual pathways. Which one is cortical and which one is subcortical?

A
  1. Retinotectal Pathway (subcortical)

2. Retinogeniculostriate Pathway (cortical)

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20
Q

Recite the visual pathways from the eye to the PVC.

A

Eye –> Optic nerve –> Optic chiasm –> Optic tract –> Superior Colliculus OR LGN.
If going to the LGN then will then go to the PVC.

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21
Q

Is there a retinotopic map in the superior colliculus?

A

Yes

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22
Q

Does damage to the retinotectal pathway prevent visual perception of contralesional targets?

A

No

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23
Q

Case study: where there was a unilateral lesion involving the right superior colliculus, how did this affect reaction time for eye movements toward contralesional targets?

A

RT much slower for contralateral stimulus in patient compared with controls. No difference between patient and controls when responding to ipsilesional targets.

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24
Q

What are the major targets of the optic tracts? Where are these targets located? (not the SC)

A

The left and right LGN, located in the thalamus, are the major targets of the two optic tracts (i.e., retinal ganglion cells synapse on LGN neurons).

25
Q

Does the right LGN receive information about the left or right visual field?

A

The left visual field.

26
Q

Most neurons in the LGN project their axons to…

A

The primary visual cortex.

27
Q

Where is the first region of the cortex to process visual information?

A

The Primary Visual Cortex, located primarily in the medial part of the occipital lobe and buried within the calcarine fissure.

28
Q

Is there a retinotopic map in V1?

A

Yes

29
Q

What kind of map exists in the PVC? What example was used to visualise this?

A

A retinotopic map.
While viewing a stimulus, a monkey was injected with a radioactive agent.
Metabolically active cells in striate cortex (V1) absorbed the agent, revealing how the topography of the retina is preserved across striate cortex.

30
Q

A 62-year-old man presented with left-sided hemianopia, there is damage to the PVC in the right hemisphere. How would he respond to a bedside test and what kind of blindness is this?

A

The patient would show a field cut – he is blind to stimuli that appear in his left hemifield.
He is cortically blind.

31
Q

What’s a scotoma?

A

A blind spot.

32
Q

What’s perimetry testing?

A

Similar to doing a bedside visual field test but more precise. Can be used for mapping of scotoma.
involves presenting a small spot of light at random locations across the visual field while the patient fixates on a central stimulus. The patient reports if they detected light.

33
Q

Complete damage to V1 within one hemisphere renders the patient…

A

… hemianopic

34
Q

How did experimenters test if humans have residual vision without V1?

A

Researchers used a task that, unlike perimetry testing, did not require explicit report but rather tapped into the patients’ implicit knowledge of their hemianopic field.
measured how quickly hemianopic patients could look at a stimulus presented in their intact hemifield as a function of whether an irrelevant stimulus (i.e., distractor) appeared in their cortically blind hemifield.

35
Q

Experiment: how quickly hemianopic patients could look at a stimulus presented in their intact hemifield as a function of whether an irrelevant stimulus appeared in their cortically blind hemifield.
What are the control and test trials?

A

Control trial – No distractor appeared.

Test trial – Simultaneous with the appearance of the target, a distractor appeared in the contralesional hemifield.

36
Q

Experiment: how quickly hemianopic patients could look at a stimulus presented in their intact hemifield as a function of whether an irrelevant stimulus appeared in their cortically blind hemifield.
What were the results? Why might this be happening?

A

The patient reported that he did not see any stimuli within the cortically blind hemifield.
Nonetheless, the latency with which he initiated eye movements toward the spot of light that appeared in the intact hemifield was slower when a distractor appeared in the cortically blind hemifield compared to when no distractor appeared.
The increase in reaction time associated with a distractor in the cortically blind hemifield can be explained by competing activation elicited by the distractor within the retinotectal pathway.

37
Q

Which visual pathway does this represent?

Eye –> Optic nerve –> Optic chiasm –> Optic tract –> Superior colliculus

A

Retinotectal pathway

38
Q

Which visual pathway does this represent?

Eye –> Optic nerve –> Optic chiasm –> Optic tract –> LGN –> V1

A

Retinogeniculostriate pathway

39
Q

Beyond the striate cortex (PVC) lie the extrastriate areas, which are higher-order visual areas that also contain representations of the retina. Which lobes do these exist in?

A

Occipital, temporal, and parietal lobes

40
Q

What are the two main projection routes from primary visual cortex (V1) to association visual cortex:

A

The ventral pathway projects to occipito-temporal association cortex and processes detailed stimulus features and object identity.
The dorsal pathway projects to occipito-parietal association cortex and processes motion, location, and spatial relationships.

41
Q

Is topography is preserved from one visual area to another?

A

Yes, each visual area has a topographic representation of the contralateral hemifield.
As one area projects to another, topography is preserved.

42
Q

Which symptoms are characteristic of brain damage involving the “what” pathway (i.e., damage to inferior occipitotemporal cortex)?

A

Inability to recognize colours
Inability to recognise objects
Inability to recognise faces

43
Q

Which symptoms are characteristic of brain damage involving the “where” pathway (i.e., damage to occipitoparietal cortex)?

A

Deficits in visual processing related to spatial localization and motion.
impaired ability to become aware of multiple parts of a visual scene.
Impaired depth perception.

44
Q

Name 3 “what” pathway syndromes.

A

Achromatopsia
Object Agnosia
Prosopagnosia

45
Q

Achromatopsia.

What is it? How did it present in the case study?

A

Inability to recognize colours due to a disruption in processing colours. Cannot name, point to, or match colours presented visually.

46
Q

How would you tell the difference between achromatopsia and colour agnosia?

A

Achromatopsia: Cortical colour blindness, as opposed to colour blindness caused by cone abnormality. Cannot name, point to, or match colours presented visually.
Whereas Colour Agnosia: Patients impaired at naming and pointing to colours presented visually, but perception of colours is preserved enabling them to match colours presented visually.

47
Q

Object Agnosia. What is it? What do symptoms suggest about this system?

A

In one example, patient exhibits difficulty reporting the name of objects based on visual information, but can provide the name based on tactile or olfactory information.
The latter behaviour indicates that the region of the brain that stores information about the objects is intact.
In another example, patient is able to identify gestures based on visual information, despite difficulty identifying objects based on visual information. This indicates that the visual deficit is quite specific.

48
Q

Prosopagnosia. What is it? In patients with this, are lesions usually unilateral or bilateral?

A

Inability to recognize faces. Patients are unable to recognize people by looking at their faces.
The usual lesion location is bilateral inferior occipitotemporal cortex.

49
Q

Name two possible results of bilateral parietal lesions.

A

Simultaneous agnosia

Impaired depth perception

50
Q

What can right parietal lesions cause?

A

Hemispatial neglect

51
Q

Simultaneous agnosia. what is it?

A

The patient shows impaired ability to become aware of multiple parts of a visual scene; reports only one object, even if two objects are spatially overlapping.
This deficit reflects a limitation of visual attention, not “tunnel vision”.

52
Q

How could you test for simultaneous agnosia?

A

Using a computer, fixate on the centre. In one scenario red dots appear, the patient should report this. In the second scenario green dots appear, the patient should report this. The last scenario red AND green dots appear, the patient might only be able to report one color.

53
Q

Explain the difference between “pure” agnosia and apperceptive agnosia.

A

Agnosia = normal perception stripped of its meaning.
“Pure” agnosia occurs in the absence of any perceptual deficits.
Pure agnosia can be contrasted with apperceptive agnosia (i.e., perceptual agnosia), for which impairment of the primary sensory modality may contribute to difficulties in recognition.

54
Q

Is it possible for a patient with agnosia to identify the object by tactile information?

A

Yes, in one video clip a patient with apperceptive agnosia (he had a field cut which contributed to his recognition difficulties) could recognise an item by touch.

55
Q

Which vascular territory would be involved in damage to the inferior occipitotemporal cortex (What pathway)?

A

Posterior Cerebral Artery

56
Q

Which vascular territory would be involved in damage to the occipitoparietal cortex (where pathway)?

A

Middle Cerebral Artery

57
Q

Damage to the occipital-parietal cortex causes…

A

Deficits in visual processing related to spatial localization and motion.

58
Q

In terms of the ‘where’ pathway, which hemisphere is thought to be more important?

A

Impairment of visuospatial analysis after a unilateral lesion occurs more commonly after damage in the right hemisphere (e.g., right parietal lobe lesions can cause hemispatial neglect).

59
Q

Which ‘where’ pathway disorders are usually a result of bilateral parietal damage?

A

Simultaneous agnosia

Impaired depth perception

Neuropsychology (15 decks)

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