Lecture 10 and 11: Visuo-perceptual Disorders Flashcards
1
Q
Name all the visuoperceptual disorders.
A
- Blindness
- Monocular vision
- Agnosia
- Apperceptive Agnosia
- Associative Agnosia
- Prosopagnosia
- Pure Alexia
- Stimultagnosia
- Unilateral Neglect
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
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
4
Q
What is homonymous hemianopia?
A
- C or E
- Cause:
- Section of:
- Optic tract or
- Optic radiations
- Section of:
- What happens?
- Loose completely on visual field
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
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
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
- Lesions:
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
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
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
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
- orienting the animal
12
Q
why did MC preserved emotion perception in faces?
A
The amygdala is the one responsible for recognizing emotions and was not damaged
13
Q
Why was MC able to navigate?
A
Navigation is processed in the posterior part of the parietal lobe, which was again undamaged
14
Q
Agnosia
A
- Problems interpreting the information
- No problem in visual cortex
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
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
- FFA
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
- FFA
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
Personal Neglect
* 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
Extra-Personal neglect
Neglect of a side of the space outside of your body
27
How do the left and right sides compare in terms of functions in the parietal area?
* Right:
* Spatial orientation
* Distribute the attention in space
* Left:
* Language
* Lesions:
* Posterior parietal area:
* no hemineglect
* Agraphia, Acalculia
28
How do we test for unilateral neglect?
* 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
What are some important white matter tracts in the right hemisphere?
* **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
What can you say about vision and brain plasticity?
* 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
