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?
Test 2: Cambridge Face Memory 2 minute discussion
Results: The family members were significantly worse than the controls at identification of the target facesAny advantages of this test?
Any disadvantages and/or problems with this test?
What do you really know from someone’s score on this test? (Hint: What do you need to do to recognise a face? Are there different steps?)
What do these results tell us about developmental prosopagnosia?
Unclear whether the deficits on the previous memory tests are:
purely memory problems, OR
problems at earlier stages processing facial identity (i.e., perceiving the identity in the first place) because such perceptual problems would prevent encoding a good memory.
Therefore, we need to test earlier stages of face perception without requiring remembering the face.
Cambridge Face Perception Test:Rationale
We need to test earlier stages of face perception without requiring remembering the face.
Also, ‘normal’ subjects show the inversion effect – they are much worse at processing inverted (upside-down) faces and don’t seem to use holistic processing very well on these faces
Therefore we’d expect the family’s greatest impairment to be for upright faces
Cambridge Face Perception Test:OVERVIEW
Arrange the six morphed faces (bottom) in order of similarity to the target face (top) – 60 seconds for each set.
Notice how the target face appears at a different orientation to the faces below.
Done with upright AND inverted faces
Cambridge Face Perception Test:Results and conclusions
Control group show significant difference between upright and inverted faces (in other words, inversion effect occurred)
Family performed worse than controls in upright and inverted conditions
Family’s showed a greater impairment relative to controls for upright faces compared with inverted faces, although they are also worse at inverted faces.
Facial Emotion Recognition Test:Rationale
Some evidence that identity processing and emotion processing are dissociable.
A test of emotion processing based on the face would allow us to see the extent of the impairment in the family.
Specific to facial identity?
Or including reading emotions from faces?
Facial Emotion Recognition Test:Method
Reading the Mind in the Eyes Test
36 items – eye region and 4 emotion state words.
Choose which word best describes the eyes.
No time limit.
Subtle discriminations required – challenging.
Facial Emotion Recognition Test:Results and Conclusions
Results:
Sample data (general pop) = 26.2/36 correct
Family scores = 26.3/36 correct
No significant impairment!
Authors’ conclusions:
The family displays normal processing of facial emotions.
More evidence that perception of facial identity is dissociable from perception of facial emotion
What do these results tell us about developmental prosopagnosia?
The family displays normal processing of facial emotions.
BUT…is the impairment specific to faces?
Is the family specifically impaired at identifying faces, or are they impaired in within-category identification in general?
Within-Category Object Recognition:Rationale
Identifying a particular face is identifying one exemplar (that particular face) of a category of objects (faces).
Are these prosopagnosics specifically impaired at identifying faces, or are they impaired in within-category identification in general?
Are there separate mechanisms for face and object processing? Or do the same mechanisms for identifying other objects apply to faces?
Within-category object recognition:OVERVIEW
Overview
Shown a series of objects (faces, cars, or guns)
Shown this set of items intermingled with new ones
Say ‘old’ or ‘new’ to each item (recognition memory)
Tests recognition memory of individual items within a broader category.
Note
This family seems to have impairment on non-face objects as well.
BUT
In previous research there have been cases of pure face-recognition deficits
What do these results tell us about developmental prosopagnosia?
Family has deficits in within-category identification of non-face objects, not just for faces, although it seems to a lesser extent.
BUT… at what level does impairment occur?
Could be impaired taking in the ‘big picture’ or gestalt – the face/object as a whole.
Could be unimpaired at processing specific details of the face/object (e.g., nose, eyes, mouth in isolation from the rest of the face).
Global-Local Task:Rationale
Does the family have a broader visual cognition deficit?
Need to test whether the family just have slower visual processing, resulting in slower psychomotor performance (translation of stimulus into a response).
Also want to test whether the family has a general global processing impairment.
Global-local task
Shown displays that contain one big (global) letter made up of lots of small (local) letters.
Must identify EITHER the large or small letter depending on instructions.
Global and local letters either match (consistent trials) or mismatch (inconsistent trials).
Vertical alignment of stimuli variedso that Ps could not just focus on asingle point in space.
Presented in blocks of 48 trials. Each block was either identifying the global letter or the local letter.
If there is a global processing impairment…
Compared with controls the family will:
Be slower on the global trials overall.
Show less interference of global letter when identifying local letter.
Show more interference of local letter when identifying global letter.
Global-Local Task:Results and Conclusions
Results
Both controls and family showed typical pattern of results on the task
No general slowness overall for family.
No evidence of global processing impairment for family members.
Conclusions
Family is not impaired in all areas of visual cognition.
General psychomotor slowness does not account for poor performance in the other tasks.
Family’s impairment on faces (and other objects) not due to a general global visual processing deficit
