CCC- Agnosia & Prosopagnosia Flashcards
When does Agnosia Typically occur?
Occurs after damage to the occipital or inferior (lower part) temporal cortex.
When individuals have Agnosia- what can’t they do?
- Can’t recognize objects- even though they can see them.
-It supports modularity- where you can get failings in different modules of object recognition.
- Different types of agnosia reveal important clues concerning the processes underlying object recognition
Apperceptive Agnosia- Mr S?
Able to move about and negotiate obstacles without difficulty.
Their grasp reveals knowledge of the size and shape (Goodale & Milner, 2004)
Low-level binding of feature of feature appears to be absent.
What damage do individuals have when they have Apperceptive Agnosia?
Damage at stage 2 (shape representation)
They are able to extract local features & can draw the local features- but can’t combine the local features appropriately into the shape representation.
Therefore- they can extract the local features- but not the actual object.
This contrasts to Associative Agnosia.
What happens in Associative Agnosia?
Copying and matching skills are unimpaired.
Patient unable to name the object despite intact knowledge.
Involves a failure in accessing knowledge about the objects.
Associative Agnosia- where in the model would there be an impairment?
Stage 3- object representation.
What is Prosopagnosia?
Profound loss in ability to recognize faces usually due to a right inferotemporal lesion.
Though unable to recognize previously familiar faces via visual input, recognition by other modalities remain intact. Thus, individuals can be identified by their voices.
Note that the ability to recognize faces is tested through overt behavioral measures. (They are asking the patient ‘who is that?’ Do you recognise them?’)
What is covert facial recognition?
Covert facial recognition is the unconscious recognition of familiar faces by people with prosopagnosia.
How can we use Skin conductance responses to see whether patients have an unconscious recognition for familiar faces?
Peak skin conductance responses (SCRs) occur 1-5 seconds after a face has been presented (red arrows).
- Peak amplitudes are larger for a familiar relative to an unfamiliar face (Tranel et al.,1985).
- Similar patterns have been observed for prosopagnosic patients (Ellis et al., 1993).
When you make a noise/ recognise someone familiar- you get a slight increase in skin conductance response- resulting in a detectable difference- so you can tell they are familiar to the person- however they still recall that they don’t know who it is.
What do patients experience with Capgras delusion?
Recognize a face and yet deny the identity of the individual.
They have no emotional response to recognising an individual- however they may say it looks like someone they know. E.g. say their mother is actually an imposter!
The loss of what stream results in prosopagnosia?
Ventral stream
The loss of what stream results in the Capgras delusion?
Dorsal
Agnosia and Prosopagnosia Case Study
John- what is he afflicted with?
Visual agnosia (failure of object recognition)
Prosopagnosia (failure of face recognition)
Doesn’t recognise wifes face- recognises her through her long hair, voice & way she walks.
Can’t recognise colours- has cortical colour blindness.
Suffered a stroke- resulted in occipital lobe in back of brain to be damaged.
Occipital lobes are the prime recipients for visual information in the brain.
Visual agnosia results from damage of what region?
Damage to the occipital or inferior
temporal cortex (early in the ventral stream)
What did Lissaur (1890) distinguish?
First distinguished different types of agnosia:
o Apperceptive: Low-level binding of features is
compromised
o Associative: Access to associated knowledge is
Compromised
