The Fusiform Face Area
A Module in Human Extrastriate
Cortex Specialized for Face
Perception
Kanwisher, N., McDermott, J., & Chun, M. M.
Is Face Recognition Special?
• Evidence from cognitive psych
– Inverted faces are disproportionately more difficult to
recognise than other inverted objects (Yin, 1969)
– Memory for precise configurations of facial features
better than for houses (Bruce et al., 1991)
– Advantage for face part recognition in context of
whole face over part in isolation larger than for house
parts (Tanaka & Farah, 1993)
• If face recognition is special, might have a
dedicated region of cortex:
– Neurons in superior temporal sulcus (STS) of
macaques fire selectively to faces
– Large N200 ERPs evoked in response to
faces, but not to other objects, in portions of
fusiform and inferotemporal gyri
– Patients with damage to occipitotemporal
region of the RH are sometimes
prosopagnosic (De Renzi, 1997)
Evidence from Imaging
• fusiform gyrus more active during:
– face recognition than during recognition of other
objects (Sergent et al.,1992)
– matching faces than matching locations (Haxby et al.,
1991, 1994; Courtney et al., 1997)
– viewing of faces than during viewing of scrambled
faces (Puce et al., 1995; Clark et al., 1996),
consonant strings (Puce et al., 1996), or textures
(Malach et al., 1995; Puce et al., 1996)
Why another imaging study?
• Although the evidence for fusiform
involvement in face recognition is
considerable, unclear whether fusiform
responds selectively to faces
• Alternative hypotheses:
– fusiform lights up because of involvement in:
• low-level feature extraction
• allocation of attention to faces due to a general attentional
bias towards faces
• subordinate level recognition of category exemplars
• recognition of any animate (or perhaps only human) objects
• The authors hoped to rule out these four
alternative hypotheses
General Design
• Part I: looked for a region of interest (ROI) on a
subject-by-subject basis that is reliably more
responsive to faces than to objects
• Part II: tested low-level feature hypothesis and
exemplar differentiation hypothesis
• Part III: tested whether ROI would respond to:
– faces viewed at an angle
– faces in which external features (e.g., hair) were
concealed
– human hands, and
– faces when attentional resources are limited by
performing a concurrent task
Technical Stuff
• In each run, twelve 6 mm slices were taken at
once, 160 times, at a rate of 1 every 2 seconds
• Slices covered all of the occipital and most of the
temporal lobes
• Voxel size: 3.25 X 3.25 X 6 mm
• Data analysis assumed a hemodynamic
response lag of 6 seconds
• For each subject, both anatomical and functional
data were fit to their own Talairach co-ordinates
Part I
• Six 30 sec stimulus epochs were
interleaved with seven 20 sec fixation
epochs
• 45 different photos, presented at a rate of
1 every 670 ms (stimulus on for 500 ms,
off for 170 ms)
• Stimulus set consisted of 180 unique
photos:
– 90 photos of students
– 90 photos of objects
• First and sixth stimulus epochs consisted
of the same set of photos, as did the
second and seventh
• Subjects were instructed to maintain
fixation during non-stimulus epochs and
(in stimulus epochs) to simply look at the
stimuli “without carrying out other mental
games at the same time”
Part I Results
• Voxels in which the MR signal was significantly
larger with passive viewing of faces than of
objects (p < 0.001) were identified
• Only region showing reliably greater activation for
faces was right fusiform gyrus
• 12/15 SJs showed fusiform activation (half in
nondominant hemisphere only, half in both
hemispheres)
– bilateral parahippocampal activation in response to
objects constitutes a double dissociation
• 2.6% signal change for faces, 0.95%
signal change for objects
• 2.74:1 ratio of signal change for
face:object epochs
• This “scouting,” done separately for each
subject, allowed the researchers to identify
areas within each subject that should light
up specifically in response to faces, in
Parts II and III
Part II, Comparison 1: Low-level
feature hypothesis
• Maybe fusiform is involved in any type of lowlevel feature extraction
• 5 of the 10 subjects from Part I showing clear
RH fusiform activation participated in Part II
• Presented two-tone versions of photographs
shown in Part I and scrambled versions of the
same photographs using Procedure from Part I
• Scrambling preserves average luminance of
intact faces and other low-level features
Results
• 1.9% signal change from baseline during
intact face epochs (identical to the change
for this subset of SJs in Part I)
• 0.6% signal change during scrambled face
epochs, difference was reliable, p < 0.05
• 3.2:1 intact:scrambled ratio
Part II, Comparison 2:
Exemplar Hypothesis
• Maybe fusiform responds to exemplars within
categories of objects
– Faces in first comparison were exemplars of a
particular category (i.e., faces!) but the objects shown
did not belong to any one category
• Procedure identical to that used in previous
comparison
– exception: houses used in place of scrambled faces
• Subjects were same five who participated in the
intact vs. scrambled faces test
Results
• 1.6% signal change for faces, 0.2% signal
change for houses, p < 0.01
• Ratio 6.6:1 faces:houses
• Fusiform activation cannot be attributed to
presentation of category exemplars
Part III, Comparison 1:
Passive Viewing of ¾ Faces vs. Hands (full attention)
• Perhaps fusiform responds to canonical
faces, or to features external to faces but
normally present in photos (e.g., hair)
• Also possible that ROI responds to any
animate thing or to any body part
• Broad sweep: Used ¾ faces with hair
hidden in one condition and pictures of
hands in the comparison condition
Results
• 2.7% signal change for faces, 0.7% signal
change for hands, p < 0.02
• 4.0:1 faces:hands ratio
• Fusiform responds to ¾ view faces, even
when hair is concealed
• Additionally, fusiform responds much more
strongly to such faces than to hands
Part III, Comparison 2
Passive Viewing ¾ Faces vs Hands (divided attention)
• Repeated procedure from previous
comparison, but subjects now had to
perform a 1-back task with stimuli rather
than passively view them
• Task was to respond whenever a repetition
in the stimulus sequence was detected
(i.e., when stimulus n and stimulus n-1
were identical)
• Purpose was to determine whether
fusiform responds not to faces selectively,
but to anything that engages general
attentional resources
• If this is so, allocating attention to a
concurrent task should reduce resources
available for attending to faces, reducing
fusiform activation
• Might get a main effect (less activation for
both faces and hands), but critical finding
would be that activation for faces =
activation for hands
Results
• 3.2% signal change for faces, 0.7% signal
change for hands, p < .005
• 4.5:1 faces:hands ratio
• Reducing available attentional resources
did not reduce fusiform activation
• Same task run in lab showed that the task
is easier with faces (92% accurate) than
with hands (86% accurate) suggesting that
the task with hands engaged attention at
least as much as it did with faces
• These data also rule out idea that fusiform
fires whenever subordinate-level
classification is required
– 1 back task with both faces and hands
required subordinate level classification to be
able to match the stimuli on trials n and n-1
Discussion
• Evidence that fusiform fires specifically to faces
– May be other areas involved as well – some
subjects showed activation in medial temporal
gyrus and in superior temporal sulcus
• Fusiform does not fire in response to:
– Low level features of faces in scrambled face stimuli
– All category exemplars
– All animate or human items
– General recruitment of attention by stimuli
• Authors note that their finding of several subjects
with bilateral fusiform activation explains why
posterior RH damage often, but not always,
produces prosopagnosia
• Patient data show double dissociations between:
– Ability to identify faces and extract emotional
expression from them
– Ability to identify faces and discriminate gaze
direction
• These findings suggest that there may be
regions of cortex specialised for functions
involved in face processing
• Possible that face processing is more
“holistic” than processing of other objects
– maybe fusiform is needed for global
processing
• Test by inducing local face processing
– Might not resolve issue because a part of a
face (e.g., nose) is not actually a face
• if subjects can process noses to the exclusion of
the rest of the face and fusiform is responsible for
face processing, not surprising if it doesn’t fire