Prospagnosia Flashcards
Oliver Sacks
Neurologist & Author.
Talks about his own experience of prosopagnosia
Prosopagnosia
The selective impairment in the ability to recognize or differentiate among faces.
‘Face blindness’
Recognition of other objects often unimpaired
Can occur with or without object agnosia
Not caused by general deficit in brain function.
Not a unitary disorder.
Different kinds of impairments.
Different levels of impairment.
Broadly, two forms:
Acquired
Caused by acute brain damage.
Developmental (congenital)
Inherited
Estimated to affect up to 2.5% of people
Based on prevalence in samples of German and Hong Kong students, but it’s not a foolproof estimate.
Faces as Objects
When thinking about prosopagnosia, we need to remember that a face is a special type of object.
Faces have a regular layout of features, and facial identity is determined by variations in the features themselves and also, crucially, their relationship to one another. Distance between eyes. Distance between eyes and nose. Size of nose relative to lips. Etc.
In general, it seems like faces undergo holistic processing.
Processed as a whole in terms of the configuration of features in relation to one another.
Holistic Processing
In general, it seems like faces undergo holistic processing and
Processed as a whole in terms of the configuration of features in relation to one another.This is what is usually impaired in prosopagnosia.
1 minute discussion: If holistic processing is impaired for prosopagnosics, is there any way they can still recognise people from their faces?
Acquired prosopagnosia and the brain.
Acquired prosopagnosia seems to occur after damage to the occipito-temporal cortex.
But frequently this is associated with general object processing deficits.
Is there a specific face-processing area of the brain?
OR are faces just a particular type of object that we’re very practiced at identifying?
Right Fusiform GyrusAka, Fusiform Face Area (FFA) McCarthy et al, 1997
Faces appear occasionally among non-objects
Greater bilateral fusiform gyrus activity when faces appear
Faces appear occasionally among known objectsGreater right fusiform gyrus activity when faces appear
These brain images are oriented as if the person is looking toward you.
Is it really just faces?
Replaced faces with flowers and didn’t get the same right fusiform gyrus activity.
Interpretation: In neurotypical adults, the fusiform face area is specialised for processing faces because it shows preferential activity for faces beyond other common objects
Is the FFA just for faces?
There is a debate as to whether the FFA is face specific or not and two general hypotheses.
The first hypothesis is the face specificity hypothesis, which states that cognitive and neural mechanisms underlying face perception are selectively engaged in perceptually processing faces and play little if any role in the perceptual analysis of nonface stimuli
The second hypothesis, the expertise hypothesis, claims that mechanisms for face processing are not engaged only by faces but are also applied in expert within-class discrimination of nonfaces
And there’s a lot of support for both!
Gauthier, Skudlarski, Gore & Anderson (2000).
They show that the FFA is activated by other objects for experts
Is it for faces? - Yes
Grill-Spector, Knouf and Kanwisher (2004) show preferential activation for faces over other objects.
Tested 12 people, 5 of whom were car experts.
Black lines denote the boundaries of the FFA
Activity shows differentiation in the areas involved in object recognition.
Faces show activation in the FFA, other objects show some overlap
Not just faces?
Both car and bird experts show FFA activation for faces.
Car experts show FFA activation for cars
Bird experts show FFA activation for birds
Experts have approximately 20 years of experience in identifying cars/birds!
Introduction
Prosopagnosic participants report genetic relatives share face recognition difficulties (~20%)
Participants in this study are people from a family that report lots of face recognition problems
Neuropsychological testing done with family which reported severe face recognition impairments
10 members of an extended family
High-functioning in everyday life
Occupations (dental student, graduate students, programmer, nurse, physician, engineer etc.) demonstrate above average intelligence.
Deficits in face memory and facial similarity
No history of early visual problems, head trauma, or birth complications
30 second-discussion – why bother getting the above data?
Test 1: Famous Faces
60 different faces shown for 5 seconds each
All pictures had hairclothing and any other
non-face informationremoved.
Correct answer: Name of person or unique identifying information
One prosopagnosic mistook Elvis Presley for Brooke Shields
Any advantages of this test?
Any disadvantages and/or problems with this test?
What do you really know from someone’s score on this test?
What do these results tell us about developmental prosopagnosia?
The prosopagnosia family were impaired relative to controls when the face was a well-known person from popular culture.
BUT…
Could be a face memory problem OR because the family lacks familiarity with people in pop culture.
Test 2 rationale
Rationale: Individuals’ exposure to famous faces varies, so not all individuals would be expected to have enough exposure to famous faces to recognise many in the test.
To overcome this, novel (new) faces were used
Test 2: Cambridge Face Memory Training phase
Given set of images with 6 new faces to learn.
30 second discussion.
Why the 3 different angles while learning?
Why more than 1 new face to learn?
Test 2: Cambridge Face Memory Test phase
Now test phase with new pictures of the target face (different angles and/or lighting).
Last section of trials has visual noise added.
30 second discussion:
Why new photos in test phase?
Why visual noise in last section of trials?
