Week 5 RF-Clinical Neuropsychology - Disorders of Object recognition Flashcards
What are the 2 main aspects in the human visual system?
- Ventral stream (inferotemporal): identity of objects.
- Dorsal stream (posterior parietal): visual control of action.
- Action in the dorsal stream relates to interacting with the objects e.g., grabbing it.
What is the purpose of the Ventral Object Pathway – Object Recognition?
- By recognising objects, it helps us make sense of the world unconsciously.
- Can recognise objects in a few hundred ms (less than 1/5th of a second).
How is our representation of the stimulus divided? (Riddoch & Humphreys, 2000)
Stimulus=chair
- Is the chair moving? (motion)
- How far away is the chair? (depth)
- We have to extract edges and the boundaries on the retina image and occurences as we rarely see objects as separate to the environment (Low-level feature processing + Perceptual Integration)
- Then we have to extract one of our own LTM representations of the chair to understand and recognise that it is a chair (these representations must contain a certain amount of information e.g., shape so we can recognise it at a later date) a limitation of this is the information must be sufficient enough so we can recognise a novel form of the chair (i.e., must be abstract so we can categorise new forms of the chair)
- These representations must be accessible
- Most theoretical models describe different stages which are needed in different cognitive tasks
- In cognitive neuropsychology we try
to ‘functionally localise’ brain damage to specific components of an underlying model of cognitive processing. - Functional localisation = finding which component/s of the system are
impaired, and which are intact. - For example, based on normal performance on low-level feature processing tasks, and impaired performance in perceptual integration, we
might assume that a patient has a deficit that is functionally localised to perceptual integration processes (e.g., You may have a stroke affecting your occipital lobe and ventral stream which interferes with the
perceptual integration processes i.e., groups features together).
What is Visual Agnosia?
- Even if unaware of object patients with visual agnosia can infer what it is e.g., by touching cutlery, they can infer whether it is a spoon or fork (i.e., adjusts using other senses).
- Depending on area of brain damaged, it can impact seeing objects but NOT facial recognition.
What are some of the main causes of acquired brain injury?
- CVAs (cerebrovascular accidents) related to ischaemic strokes (blocked supply disrupting the blood supply)
- CVAs related to hemorrhagic strokes (bleeding in the brain)
- TIAs or transient ischaemic attacks (mini-strokes)
- Viral infections (e.g., HIV causing encephalitis or inflammation on the brain)
- Closed head injury (accidents, assaults)
- Hypoxia resulting from poisoning (e.g., carbon monoxide)
- Degenerative illnesses (e.g., Parkinson’s disease; Alzheimers).
-These are on the assumptions that the individual does not have any neurodegenerative diseases, genetic issues or other brain damage prior (i.e., it is usually sudden)
-Mini-strokes can occur without someone realising e.g., when sleeping, and can resolve itself with no real effect on the individual unless found later when doing a brain surgery. They are pretty vocal and
can affect very small parts of brain tissues (can do large too). Where it occurs is random and depends on the cerebrovascular system, veins, blood supply etc.,
-Hemorrhages have more severe effects however
-Some viruses affect the brain via parainfectious actions e.g., COVID-19 does not directly attack brain tissue, BUT can cause brain inflammation and swelling (aka encephalitis) where if this lasts for too
long, has damaging effects on the brain
-Head injury causes localised damage to the brain causing cognitive and behavioural impairments
-Parkinson’s disease is associated with problems with movement, can also have impacts on cognitive functions as this disease is not just affecting the motor system.
What is the Neuropsychological profile of patient IES?
- 75 year old male.
- Bilateral posterior cerebral artery (PCA) stroke involving the ventral occipital lobes including the fusiform and lingual gyrus on the left and fusiform gyrus on the right.
- Also some damage to the left hippocampus and primary visual cortex (inferior to calcarine fissure resulting in upper right quadrant visual field loss – quadrantanopsia).
- Clinical diagnosis of visual object agnosia and prosopagnosia without alexia.
- Achromatopsia (colour blindness).
- No language comprehension or production problems.
- No loss of semantic knowledge.
- Had quite severe amnesia following damage to left hippocampus.
- Object agnosia is an acquired impairment for visual object recognition WHEREAS prosopagnosia is an impairment with facial recognition, Alexia is an impairment in word recognition affecting the ability to read.
What was found in the MRI scans for patient IES? (coronal sections)
- Left lingual gyrus involvement
- Bilateral fusiform gyrus lesions
- Lesion encroaching on the primary visual cortex (inferior part of calcarine fissure)
- This arises because he has lost brain tissue that processes sensory information for one quadrant of the retina meaning you lose the ability to visualise sensory information from one corner of the visual field.
- Upper right quadrant visual field loss – quadrantanopsia
How well did IES do in regard to object processing?
- IES: BORB Picture Naming 23/76 (32.8%)
- IES: Real objects 12/20 (60%)
- Those who have experienced a stroke struggle with specific things visually despite fluent speech e.g., asking patients to name line drawings of objects (which he struggled to do)
- This patient was slightly better at recognising real objects
How well did IES do in regard to object naming error?
- Study note: Some errors are both visual
and semantically related. The errors can provide information about functional localisation of the deficit. - The nature of response they give when unable to identify the object is interesting as they are missing some visual information.
- His visual system isn’t able to clearly interpret the objects as you would expect.
Riddoch & Humphreys (2000):
* Visual errors might be assumed to arise from damage to the perceptual system BEFORE access to any kind of semantic
information.
- Semantic errors might be assumed to arise from damage to the perceptual
system AFTER access to semantic information.
How well did IES do in regard to face recognition?
- IES: Famous Face Naming 1/30 (3% correct)
- Study note: Typically, face stimuli have to be selected to match the age (background and other factors) of the patient. You will know Winston Churchill, but maybe not Grace Kelly (famous actress & Princess of Monaco!). Poor face recognition = Prosopagnosia.
- He was asked to name famous people but only got one person correctly
How well did IES do in regard to reading?
- Single word reading (printed) 50/50
- Regular words: 13/15
- Irregular words: 15/15
- Letter naming: 25/26
- Lexical decision: 29/30
IES: Mixed case/font reading 21/24
Study note: This is one of the most striking aspects about IES: His impaired object and face recognition, but remarkably preserved (unaffected) reading. This raises questions about whether the perceptual system has ‘domain-specific’ processes for objects, faces and words.
- His reading is incredibley well preserved
- It tells us that the way the brain is organised, it seems to have separate processes for different stimuli
How well did IES do in regard to Line Cancellation Test?
- Had to cross out all the lines which some had problems processing on one side (not him)
- Just had to say whether lines were the same length and circles were the same diameter
- It seems he just performed at a chance level (just guessed)
- This shows no evidence of hemispatial neglect
How well did IES do in regard to BORB tests of low-level visual processing?
- IES: 10/20 (50%)
- IES: 11/20 (55%)
- IES shows some problems in line length matching and size matching = Deficit in low-level feature perception
- His ability to copy complex images is impaired
- Has some global spacial disorganisation
How well did IES do in regard to Rey Figure shows evidence of poor perceptual organisation?
- Shows another attempt he made in 10 minutes and missed a lot of features.
Rey Figure score:
* IES: 16/36
* Controls 33.5/36
- The person has to trace the outlines of all the objects they see (in this case 4)
- He had difficulty segmenting these displays
What did IES results in Overlapping Figures Test indicate? (for poor perceptual organisation evidence)
- Study note: In this test IES had to trace the outline of each object in the overlapping displays. You can see that sometimes he was successful (e.g., the spoon), but for other items he included edges of more
than one object (he was unable to name any of the display objects). - His perceptual system has difficulties integrating objects seperately despite occlusions.
- IES shows evidence of impaired perceptual organisation/integration
in the Rey Figure and Overlapping Figures
tests.
