Lecture 10 and 11: Visuo-perceptual Disorders

Question 1

Name all the visuoperceptual disorders.

Answer 1

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

Question 2

What is monocular vision?

Answer 2

• 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

Question 3

What is bitemporal hemianopia?

Answer 3

• 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

Question 4

What is homonymous hemianopia?

Answer 4

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

Question 5

Blindness

Answer 5

• 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

Question 6

What is Blindsight?

Answer 6

• 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

Question 7

Give an example of how blindsight was studied

Answer 7

• 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

Question 8

What is Riddoch phenomenon?

Answer 8

• 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

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

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

Question 11

Where are the superior colliculi? and what are they?

Answer 11

• 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

Question 12

why did MC preserved emotion perception in faces?

Answer 12

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

Question 13

Why was MC able to navigate?

Answer 13

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

Question 14

Agnosia

Answer 14

• Problems interpreting the information
• No problem in visual cortex

Question 15

Apperceptive Agnosia

Answer 15

• 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

Question 16

Apperceptive Agnosia

Answer 16

• 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

Question 17

Associative Agnosia

Answer 17

• 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

Question 18

Give an example of apperceptive agnosia

Answer 18

• 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

Question 19

What is Prosopagnosia?

Answer 19

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

Question 20

Prosopagnosia

Answer 20

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

Question 21

Simultagnosia

Answer 21

• 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

Question 22

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

Answer 22

• 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)

Question 23

Unilateral Neglect

Answer 23

• 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

Question 24

Anosognosia

Answer 24

Unaware of their deficits

Question 25

Personal Neglect

Answer 25

• 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

Question 26

Extra-Personal neglect

Answer 26

Neglect of a side of the space outside of your body

Question 27

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

Answer 27

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

Question 28

How do we test for unilateral neglect?

Answer 28

• 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

Question 29

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

Answer 29

• 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

Question 30

What can you say about vision and brain plasticity?

Answer 30

• 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