Lecture 10 and 11: Visuo-perceptual Disorders Flashcards
Name all the visuoperceptual disorders.
- Blindness
- Monocular vision
- Agnosia
- Apperceptive Agnosia
- Associative Agnosia
- Prosopagnosia
- Pure Alexia
- Stimultagnosia
- Unilateral Neglect
What is monocular vision?
- 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
What is bitemporal hemianopia?
- 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
What is homonymous hemianopia?
- C or E
- Cause:
- Section of:
- Optic tract or
- Optic radiations
- Section of:
- What happens?
- Loose completely on visual field
Blindness
- 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
What is Blindsight?
-
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
Give an example of how blindsight was studied
- 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:
What is Riddoch phenomenon?
- 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
Give an example of a patient showing Riddoch’s Phenomenon.
- 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
While doing some fMRI scans on MC, it was noticed that there was some activation in MT/V5, how?
- It was found that there is a subcortical connection that from the eyes to the superior colliculi to the thalamus
Where are the superior colliculi? and what are they?
- 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
why did MC preserved emotion perception in faces?
The amygdala is the one responsible for recognizing emotions and was not damaged
Why was MC able to navigate?
Navigation is processed in the posterior part of the parietal lobe, which was again undamaged
Agnosia
- Problems interpreting the information
- No problem in visual cortex
Apperceptive Agnosia
- 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