1. COGS 172 VISION CONTINUED Visual form agnosia

2. Visual form agnosia
PRESERVED acuity, brightness discrimination, color vision, & other elementary visual capabilities. Sometimes preserved shape from motion.
SEVERELY IMPAIRED form perception (pictures, letters, simple shapes, objects)
They do not have memory problems or dementia, they have knowledge of the objects.
How to test?

3. Visual form agnosia
PRESERVED acuity, brightness discrimination, color vision, & other elementary visual capabilities. Sometimes preserved shape from motion.
SEVERELY IMPAIRED form perception (pictures, letters, simple shapes, objects)
They do not have memory problems or dementia, they have knowledge of the objects.
How to test?
Allowing patient to touch the object can help differentiate between a visual disorder vs. a deficit at the level of object knowledge

4. Videos Object Agnosia 1, 2, 3 What do you think?
I’m not very sure. Guess in a minute? You got me… (when she touches) … Of course, I know what this is already, it’s a clothespin.
You won’t let me touch it? Gosh - It could be so darn many things… I don’t think I could guess that… (immediately after touching)… Lord, it’s a piece of soap.
That’s a … (seems to know it but slow to name). A pin, a safety pin.
You got me. (touches it) It’s a piece of soap. (smells it). Oh it’s a candle.
What do you think?
Note the kinds of questions/tasks used to assess agnosia
What aspects of processing are impaired?
What aspects are spared?

5. Videos
I’m not very sure. Guess in a minute? You got me… (when she touches) … Of course, I know what this is already, it’s a clothespin.
You won’t let me touch it? Gosh - It could be so darn many things… I don’t think I could guess that… (immediately after touching)… Lord, it’s a piece of soap.
That’s a … (seems to know it but slow to name). A pin, a safety pin.
You got me. (touches it) It’s a piece of soap. (smells it). Oh it’s a candle.

6. Apperceptive Associative
Visual Agnosia
Apperceptive Associative

7. The “copy” test
Apperceptive agnosia is mainly characterized by failures in object recognition linked to problems in perceptual processing
Patients cannot recognize, copy, or match objects.
 Mr S. Benson & Greenberg 1969

8. Apperceptive Associative
Impairment in drawing copies

9. Associative Agnosia Trouble recognizing objects visually
Can copy – at least some perceptual processing preserved!
“Higher level”
Where is the deficit? Could deficit be in matching visual objects to stored object representations? Is it at all perceptual? Could it be disconnect between percept and memory representations?
Some perceptual deficits likely
Perceptually similar errors
Copying is piecemeal, slow
Rubins & Benson 1971

11. How do agnosic patients get by?
Other modalities - touch, sound etc.
Other visual cues
Color
Motion
Form from motion
Context
Piece together multiple cues… General reasoning

12. Lesion tendencies Apperceptive: Occipito-temporal
Sometimes inferior parietal
Associative:
Occipitotemporal

13. Agnosia Much variability among patients
The idea of loss of global or “gestalt” perception
“Integrative agnosia” -- sometimes patients guess based on a feature or part but cannot bind into a whole; brief presentation not enough
Role of tracing, motion

14. Special subclasses of objects: Faces and words
Prosopagnosia: “Face-blindness”. Impairment in the recognition of faces. Often accompanied by other impairments (e.g., place or object recognition, facial expression of emotion). Can be restricted. Use voice, hair, body movements etc.
Alexia: Unable to read. Patients with “alexia without agraphia” will be able to write but not read (a dissociation)
Animation:
Are these distinct “modules”? Are they correlated? What can agnosic patients tell us?

15. Powerful deductive tools in brain disorders
Associations
Dissociations
Double dissociations
Important
- clinically
- in understanding the brain

16. Associations Behavior A and Behavior B are affected together
Suggests a relationship; not strong evidence
There may be separate areas, damaged because they are close together, or different neural populations
What can help?

17. Associations Behavior A and Behavior B are affected together
Suggests a relationship; not strong evidence
There may be separate areas, damaged because they are close together, or different neural populations
What can help? B A
A correlation in the degree of deficit between A and B: More likely for there to be a relationship between the two – though keep in mind, correlation ~= causation

18. Dissociations Behavior A impaired, Behavior B spared
So they are independent
Not necessarily
Maybe one task is “easier”
Patients fail at the harder task. Spared regions of brain carry out easy task
To show a dissociation, studies must match task difficulty, attentional demands, etc.
Do deficit patterns resemble “normal” performance”? (e.g., college students “under stress” – more detail in aphasia lectures) B A

19. Double Dissociations
Behavior A impaired - Behavior B spared in one patient/group
Behavior B impaired - Behavior A spared in one patient/group
Strong evidence
At least it is possible for A and B to show independence B A
A DD between two tasks does not necessarily imply a DD between cognitive processes (Shallice, 1988)
E.g. “lesioned” neural network models with no obvious modular structure can produce data that looks like a DD (Plaut, 1995).

20. Object Categories and Agnosia
Face
Object
Printed Word
Face, or face and object: mostly bilateral, sometimes right hemisphere lesions
Word, or word and object: can occur with unilateral left
Most common lesion site in medial ventral temporal regions (fusiform, lingual, parahippocampal, gyri); sometimes more superior and lateral temporal lesions also

21. A little more about faces… - Very important class of stimuli - Strong arguments have been made for localization, modularity and domain-specificity in face processing

22. Face Processing Tests Famous faces test
Facial expressions (many patients can do)
Matching tests
Match face to different viewpoint
Match face to one you just saw (correct vs. incorrect)
Memory tests (recall, recognize)
Custom tests/experiments

23. Prosopagnosia: Lesion Sites
Fusiform and lingual gyri are often implicated. Bilateral, if unilateral often right hemi,

24. But… sometimes there is no lesion
Congenital or Developmental Prosopagnosia
Face recognition impairments with no known lesion or clear neurological cause
Intact “fusiform face area” and ventral visual regions - in fact intact brain!
Opportunity to test functional (e.g., fMRI, ERP) or structural (e.g., anatomical structure, connectivity) correlates of behavioral deficits in the absence of a lesion (e.g., Gilaie-Dotan, Bentin, Harel, Rees, & Saygin, 2011)
Are they the people who are really really bad at face recognition on a continuum? Or is there a binary (yes/no) deficit?