Lecture 10 and 11: Visuo-perceptual Disorders Flashcards

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1
Q

Name all the visuoperceptual disorders.

A
  • Blindness
  • Monocular vision
  • Agnosia
    • Apperceptive Agnosia
    • Associative Agnosia
  • Prosopagnosia
  • Pure Alexia
  • Stimultagnosia
  • Unilateral Neglect
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2
Q

What is monocular vision?

A
  • Is also called hemianopia
  • A in the image
  • blindness in one hemifield
  • You can see more if you move your eyes
  • Causes:
    • Brain tumour or damage to the primary optic pathway
  • Other types:
    • Bitemporal hemianopia
    • Homonymous hemianopia
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3
Q

What is bitemporal hemianopia?

A
  • B in the image
  • Loose peripheral vision
  • Caused:
    • Section of the optic chiasm
    • Tumour in the optic chiasm
  • What happens?
    • Each eye sends to the brain information from the controlateral visual field
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4
Q

What is homonymous hemianopia?

A
  • C or E
  • Cause:
    • Section of:
      • Optic tract or
      • Optic radiations
  • What happens?
    • Loose completely on visual field
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5
Q

Blindness

A
  • Caused:
    • ablation of V1
  • Lesions:
    • Lesion on the right striate cortex, means that you can’t see what is in the left visual field
    • vice vers
  • You can still be aware of things
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6
Q

What is Blindsight?

A
  • Unconscious residual vision following lesions or ablation of V1
    • Can still detect and identify visual stimuli
  • In some cased, might have son conscious vision
    • Only when high contrast stimuli that move
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7
Q

Give an example of how blindsight was studied

A
  • Helen the monkey
    • bilateral destruction of V1
    • She can:
      • orient towards
      • follow
      • grasp
      • detect
      • localize
      • discriminate
    • visual objects
  • Patient DB:
    • Lesions:
      • visual cortex:
    • Procedure:
      • The experimenters would flash light and the participants had to guess where the flash happened
      • Show to stimuli and the participants had to guess what was the stimuli
    • Results:
      • Shift of the eyes to the flashing, Reach with a finger
      • Well above chance and they could discriminate the direction of a moving object
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8
Q

What is Riddoch phenomenon?

A
  • When a patient is unable to see static objects but has a preserved awareness for moving ones
  • Patients can use motion to navigate around objects
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9
Q

Give an example of a patient showing Riddoch’s Phenomenon.

A
  • MC
  • Lesion:
    • bilateral visual cortex
  • Symptoms:
    • Completely blind to static objects
    • Use sense of motion to navigate
    • Discriminated the affective aspects of a face
      • but couldn’t recognize the person
  • As you can see from the image bellow, most of the occipital love is damaged
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10
Q

While doing some fMRI scans on MC, it was noticed that there was some activation in MT/V5, how?

A
  • It was found that there is a subcortical connection that from the eyes to the superior colliculi to the thalamus
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11
Q

Where are the superior colliculi? and what are they?

A
  • Midbrain
  • Responsible for the transformation of sensations into movement
  • Major role:
    • orienting the animal
      • specifically the eyes to the objects of interest in the outside world
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12
Q

why did MC preserved emotion perception in faces?

A

The amygdala is the one responsible for recognizing emotions and was not damaged

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13
Q

Why was MC able to navigate?

A

Navigation is processed in the posterior part of the parietal lobe, which was again undamaged

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14
Q

Agnosia

A
  • Problems interpreting the information
  • No problem in visual cortex
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15
Q

Apperceptive Agnosia

A
  • Problem with perception encoding
  • Similar to blind
  • Can’t
    • integrate parts of an image into a whole
    • copy images
  • Can
    • Appropriately reach or grab aobjects
  • Lesions:
    • bilateral infero-occipto-temporal lesion
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16
Q

Apperceptive Agnosia

A
  • Problem with perception encoding
  • Similar to blind
  • Can’t
    • integrate parts of an image into a whole
    • copy images
  • Can
    • Appropriately reach or grab aobjects
  • Lesions:
    • bilateral infero-occipto-temporal lesion
17
Q

Associative Agnosia

A
  • Problem with associating something perceived with semantical knowledge allowing to interpret it
  • Can’t:
    • identify an object
    • draw from memory
  • Can
    • copy
    • do object matching
    • basic perceptual functions
  • Lesions
    • Occipit-temporal (more anterior) such that disconnects visual areas from the semantic areas
18
Q

Give an example of apperceptive agnosia

A
  • Patient DF
  • Can’t:
    • report orientation of single lines or objects
  • Can:
    • manipulate an object for it to be in a given orientation
    • Reach towards objects
19
Q

What is Prosopagnosia?

A
  • Also known as face agnosia
  • Can’t
    • discriminate between faces
  • Can
    • discriminate objects
    • Sometimes facial expressions
  • Lesion:
    • FFA
      • Fusiform Face Area
20
Q

Prosopagnosia

A
  • Also known as face agnosia
  • Can’t
    • discriminate between faces
  • Can
    • discriminate objects
    • Sometimes facial expressions
  • Lesion:
    • FFA
      • Fusiform Face Area
21
Q

Simultagnosia

A
  • Impairment to process complex images or multiple objects at the same times
  • Visual-spatial attentional problem
  • Can’t
    • Hard to process when multiple objects are presented simultaneously
    • name nonwords
  • Can
    • Recognize objects when they are presented one at the time
    • Count objects
    • navigate normally
    • see scenes but can’t identify them
    • name words
  • Lesion:
    • Dorsal stream
22
Q

Why would a patient with simultagnosia be unable to name nonwords compared to regular words?

A
  • They perceive a normal word as a whole and so as just one object
  • Nonword is perceived as a string of letters (many objects together)
23
Q

Unilateral Neglect

A
  • also known as hemineglect
  • Patient is not aware of what is in one half of the space
    • the half that is contralateral to the lesion site
  • Most of the time they also suffer from anosognosia
  • Lesions:
    • mostly right hemisphere, parietal lobe
24
Q

Anosognosia

A

Unaware of their deficits

25
Q

Personal Neglect

A
  • Ignore the contralateral side of their bodies given a lesion
  • Lesion
    • Parietal lobe
  • ex)
    • Neglect to shave the left side of their face
    • or put the left sleeve of a sweater
26
Q

Extra-Personal neglect

A

Neglect of a side of the space outside of your body

27
Q

How do the left and right sides compare in terms of functions in the parietal area?

A
  • Right:
    • Spatial orientation
    • Distribute the attention in space
  • Left:
    • Language
    • Lesions:
      • Posterior parietal area:
        • no hemineglect
        • Agraphia, Acalculia
28
Q

How do we test for unilateral neglect?

A
  • There are two tests that we can perform:
    • Line bisection test:
      • Instructions:
        • Place a mark with a pencil through the centre of a series of horizontal lines
      • Results:
        • Hemineglect: Places the line at the same place on the sheet regardless of the horizontal line is shifted to one side or the other
    • Cancellation test:
      • Instructions:
        • Cross out all the lines
        • or Search for all Xs in many letters
      • Results:
        • crosses all the lines on one side of the page only
        • finds all the Xs on one side of the page only
29
Q

What are some important white matter tracts in the right hemisphere?

A
  • Superior Longitudinal Fasciculus
    • Right Posterior Inferior Parietal area:
      • spatial processing
    • Damage:
      • causes chronic unilateral neglect
      • Failure to attend to spatial information in the contralateral visual field yielding unilateral neglect
30
Q

What can you say about vision and brain plasticity?

A
  • For patients who are congenitally blind
    • it was shown that the non-visual functions expand to the visual areas in order to improve these non-visual senses
      • Activation of visual areas for sound and auditory processing
      • And touch and smell