NeuroImage 83 (2013) 408–417
Contents lists available at ScienceDirect
NeuroImage
journal homepage: www.elsevier.com/locate/ynimg
The fusiform face area responds equivalently to faces and abstract
shapes in the left and central visual fields
Scott D. Slotnick ⁎, Rachel C. White
Department of Psychology, Boston College, Chestnut Hill, MA, USA
a r t i c l e
i n f o
Article history:
Accepted 9 June 2013
Available online 15 June 2013
Keywords:
Shape
Face
Visual field
FFA
OFA
fMRI
a b s t r a c t
The fusiform face area (FFA) is widely believed to be specialized for processing faces. Although the FFA is most
responsive to faces, this region also consistently responds to non-face items. This suggests that the FFA may be
tuned to a feature that is shared by faces and non-face items. Based on the known left visual field face-processing
bias along with evidence that the FFA responds to the visual feature of shape, we hypothesized that the FFA may
be particularly tuned to shapes presented in the left visual field. We tested this hypothesis using functional magnetic resonance imaging (fMRI). In a face localizer run, participants viewed blocks of faces or objects. In a separate run, blocks of intact or scrambled abstract shapes were presented in the left, the central, or the right visual
field. Within each of the eleven face-processing regions-of-interest (identified by contrasting faces and objects),
the magnitude of activity associated with faces was compared to the magnitude of activity associated with intact
shapes. Consistent with previous results, collapsing over shape visual field location, the magnitude of activity associated with faces was greater than the magnitude of activity associated with shapes in the FFA. However, separating by shape visual field location revealed an equivalent magnitude of activity associated with faces and
shapes in the FFA when shapes were presented in the left and central visual fields. These findings indicate that
the FFA, rather than being specialized for holistic face processing, mediates shape processing in the left and central visual fields.
© 2013 Elsevier Inc. All rights reserved.
Introduction
The fusiform face area (FFA) is a circumscribed region in the right
ventral temporal cortex that is widely believed to be specialized for
processing faces. The FFA was first identified based on fMRI evidence
that this region produced a greater response to faces than objects,
hands, houses, or scrambled faces (Kanwisher et al., 1997). Subsequent fMRI studies reported additional evidence that the FFA is specialized for face processing (Downing et al., 2006; Gilaie-Dotan et
al., 2008; Grill-Spector et al., 2004; Kanwisher et al., 1998, 1999;
Tong et al., 2000; Tsao et al., 2008; Xu et al., 2012). Specifically, the
magnitude of FFA activity produced by faces was approximately
twice (mean 2.1 times, range 1.4–2.8 times) the highest magnitude
of activity produced in this region by non-face items (i.e., in the preceding studies, objects, bodies, houses, cars, inverted Mooney faces,
bodies, objects, bodies, and Chinese characters, respectively).
Although the previous evidence has been taken to illustrate that
the FFA selectively processes faces, it is important to highlight that
⁎ Corresponding author at: Department of Psychology, Boston College, Chestnut Hill,
MA 02467, USA. Fax: +1 617 552 0523.
E-mail address: [email protected] (S.D. Slotnick).
1053-8119/$ – see front matter © 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.neuroimage.2013.06.032
the magnitude of activity produced by non-face items in this region
(1.0 ± 0.11% signal change; mean ± 1 se) was also significantly
greater than 0 (p b 0.001; Gilaie-Dotan et al., 2008; Grill-Spector et
al., 2004; Kanwisher et al., 1997, 1998, 1999; Tong et al., 2000; Tsao
et al., 2008). In regard to such non-face FFA activity, Desimone
(1991) made a pertinent point regarding the possible existence of
face-selective cells in the monkey:
The greater the response to non-face stimuli, the more likely it is
that a cell is actually tuned to some more general object feature,
such as shape or texture. (p. 3)
There is some evidence that the FFA responds to the visual feature
of shape. Perception of abstract sculptures (Grill-Spector, 2003) and
curvilinear patterns (Caldara and Seghier, 2009) – which are defined
primarily by shape – produced activity in the FFA, and abstract shape
memory produced activity at the known location of the FFA (Ross and
Slotnick, 2008). Chinese character perception, which is arguably a
shape-dependent process, also activated the FFA (Xu et al., 2012).
The FFA was also activated in radiologists who detected abnormalities
in chest radiographs (Harley et al., 2009) and in chess experts when
they processed naturalistic chess positions (Bilalić et al., 2011), who
may have relied on shape extraction to some degree. If the FFA is involved in processing shape, it would explain why this region consistently responds to both face and non-face items that are composed
of external and internal shapes.
S.D. Slotnick, R.C. White / NeuroImage 83 (2013) 408–417
Although it is possible that the FFA processes the visual feature of
shape, to date, this region has always produced the greatest response
to faces, which supports the notion that it is specialized for holistic
face processing. Of relevance, behavioral and split-brain patient evidence has shown that face processing in the left visual field is superior
to face processing in the right visual field (for a review, see Yovel et
al., 2008). As such, we hypothesized that the FFA may be particularly
tuned to processing shape in the left visual field. In the present fMRI
study, we tested this hypothesis by identifying face processing activity
using a blocked face-object stimulus protocol (Fig. 1A). The face versus
object contrast was used to identify previously reported face-processing
regions-of-interest (ROIs) including the right and left FFA, the right and
left occipital face area (OFA), the right and left face-selective region in
the superior temporal sulcus (fSTS), the right and left amygdala, the
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right anterior temporal face patch (ATFP), the right orbital frontal cortex (OFC), and the right inferior frontal sulcus (IFS) (Chan and
Downing, 2011; Grill-Spector et al., 2004; Haxby et al., 2000; Jiang et
al., 2011; Liu et al., 2010; Nasr and Tootell, 2012; Rajimehr et al.,
2009; Tsao et al., 2008). Shape-processing activity was identified
using a blocked stimulus protocol in which intact or scrambled abstract
shapes were presented in the left visual field, the central visual field, or
the right visual field (Fig. 1B). For each face-processing ROI, the magnitude of activity associated with faces was first compared to the magnitude of activity associated with intact shapes collapsed over visual field
location, in an effort to replicate previous findings, and then the magnitude of activity associated with faces was compared to the magnitude of
activity associated with intact shapes as a function of visual field location. To anticipate a critical result, the magnitude of activity associated
Fig. 1. Stimulus protocols. A. The face localizer consisted of 14 s blocks of faces or objects. B. The shape localizer consisted of 14 s blocks of intact shapes or scrambled shapes
presented in the left visual field, the right visual field, or the central visual field.
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with faces in the right FFA was statistically equivalent to the magnitude
of activity produced by shapes presented in the left and central visual
fields.
Materials and methods
Participants
Twelve adults (4 females, 8 males, mean age 23.2 years, age range
20.8–26.7) with normal or corrected-to-normal visual acuity participated in the study. The protocol was approved by the Boston College
Institutional Review Board and informed consent was obtained.
Stimulus protocols
During the face localizer run, alternating blocks of Caucasian faces
(Tarr, 2011a) and common colored objects (Tarr, 2011b) were presented
at the center of the screen (Fig. 1A). Faces spanned 3.2–5.0° by 3.8–5.7° of
visual angle and objects spanned 1.3–5.0° by 1.9–5.7° of visual angle
(width by height). Each of the 16 blocks (8 blocks × 2 stimulus types)
lasted 14 s and consisted of 10 stimuli with no inter-stimulus-interval.
There were 10 s fixation periods at the beginning and end of the run,
and there were no rest periods between blocks. The total run duration
was 244 s. Half of the faces were females and the other half were
males. Stimuli were randomized and presented twice. Participants
were instructed to classify approximately half of the faces and half of
the objects as pleasant and classify the other half of the faces and the
other half of the objects as unpleasant. It was emphasized that this was
a relative judgment (e.g., if a participant perceived most or all of the
faces as pleasant, they were instructed to classify about half of the faces
as more pleasant). This required participants to track their previous judgments, to some degree, throughout the task.
During the shape localizer run, blocks of intact or scrambled abstract
shapes were presented in the left visual field, the central visual field, or
the right visual field. Each shape was constructed by connecting four
pseudo-randomly generated Bézier curves connected end-to-end
(Fig. 1B). None of the shapes were similar to either animals or objects
(for shape construction details, see Slotnick and Schacter, 2004). Scrambled shapes were constructed by sectioning each shape into 100 equal
squares (in a 10 by 10 matrix) and randomly assigning the locations of
these squares, without replacement, within the original bounding box.
Shapes spanned 6.8° of visual angle with the nearest edge of peripheral
shapes 3.7° of visual angle from fixation. Each of the 36 blocks (6
blocks × 2 shape types × 3 visual field positions) lasted 14 s and
consisted of 14 stimuli with no inter-stimulus-interval. There were 10 s
fixation periods at the beginning and end of the run, and there were no
rest periods between blocks. The total run duration was 524 s. The
order of blocks was random with the constraints that no more than 3
blocks of intact or scrambled shapes were presented sequentially and
that stimuli in successive blocks were never presented in the same visual
field location. The participants were instructed to maintain central fixation and detect an infrequently occurring red square that was flashed
for 1 s at a random location within the stimulus stream.
Data acquisition and analysis
Images were acquired at the Harvard Center for Brain Science on a
Siemens 3 Tesla Trio Scanner with a standard head coil. A magnetization
prepared rapid gradient echo sequence was used to acquire anatomic
data (TR = 30 ms, TE = 3.3 ms, flip angle = 40°, field-of-view =
256 × 256 mm2, acquisition matrix = 256 × 256, slices = 128, slice
thickness = 1.33 mm, 1.33 × 1 × 1 mm resolution). An echo planar
imaging sequence was used to acquire functional data (TR = 2000,
TE = 30 ms, flip angle = 90°, field-of-view = 256 × 256 mm2, acquisition matrix = 64 × 64, slices = 32, slice acquisition order = interleaved bottom-to-top, slice thickness = 4 mm, no gap, 4 mm isotropic
resolution). To avoid magnetic saturation, the first 2 volumes
(timepoints) were discarded and replaced by the 3rd volume.
BrainVoyager QX (Brain Innovation B.V., Maastricht, The Netherlands)
was used to conduct the analysis. Default functional data preprocessing included slice-time correction, motion correction (one-pass
alignment of all volumes in each run to the first volume), and removal
of linear trends and temporal components below 2 cycles per run
length. To maximize spatial resolution, spatial smoothing was not
conducted. The fMRI time series was not corrected for temporal dependencies according to an autoregressive correlation structure. For normalization, all images were transformed into Talairach space based on
the anatomic locations of the most anterior, posterior, inferior, superior,
left, and right points in addition to the location of the anterior commissure and the posterior commissure (these points were identified on
each anatomic volume and then the same transformation was applied
to the corresponding functional volumes).
A group-level random-effect general linear model analysis was
conducted for all contrasts. For each participant, each event type was
modeled by convolving a canonical hemodynamic response with a
square-wave defined by the corresponding onsets and durations. The
first-order individual participant results (i.e., event beta-weight magnitudes) were entered into the second-order group analysis. For the
group results, a threshold of p b 0.001 (t = 3.093) was enforced. This
yielded a false discovery rate correction for multiple comparisons to
p b 0.01 for all contrasts. To aid in visualization, activity was projected
onto the cortical surface reconstruction of a representative participant
(for cortical segmentation details, see Slotnick, 2005).
The group-level face versus object contrast was used to isolate activity associated with processing faces (Downing et al., 2006; Gilaie-Dotan
et al., 2008; Nasr and Tootell, 2012; Rajimehr et al., 2009), which was
projected onto the group average anatomic image. The center of each
face-processing ROI, the selection of which was guided based on previous findings (Chan and Downing, 2011; Grill-Spector et al., 2004; Haxby
et al., 2000; Jiang et al., 2011; Liu et al., 2010; Nasr and Tootell, 2012;
Rajimehr et al., 2009; Tsao et al., 2008), was identified as the coordinate
with the most significant activation within a given cortical region. Each
ROI consisted of all the voxels within a 5 × 5 × 5 mm cube centered at
that coordinate. This relatively small volume, which was slightly larger
than 1 functional voxel, was selected to maximize spatial resolution. Although the FFA constituted the primary ROI, other ROIs were analyzed
to provide a more complete picture of face processing. For each ROI, activation timecourses from −2 to 24 s after block onset were linear
trend corrected and baseline corrected from −2 to 0 s (i.e., for each
event type, a constant was added to the activation timecourse such
that the mean magnitude of baseline activity was equal to 0% signal
change). It is notable that an activation magnitude of 0 refers to the
baseline level of activity. Statistical analysis was based on the average
magnitude of each event's activation timecourse from 6 s (the expected
initial peak of the hemodynamic response) to 14 s (block offset). For a
given ROI, activation timecourse magnitudes were statistically compared and the corresponding significance level was reported to
p b 0.05, p b 0.01, or p b 0.001. These activation timecourse significance values could deviate from the beta-weight significance values,
as the timecourse analysis and the beta-weight analysis had different
baselines and the sensitivity of these methods can differ in the same
cortical region (Slotnick, 2005).
Results
Contrast results
The face versus object contrast produced activity in the right and left
OFA, the right and left FFA, the right and left fSTS, the right and left
amygdala, the right ATFP, the right OFC, and the right IFS, while the reverse contrast produced activity in many cortical regions including the
parahippocampal gyrus (Fig. 2A; Table 1 provides face-processing
S.D. Slotnick, R.C. White / NeuroImage 83 (2013) 408–417
coordinates and maximum t-values). Activation timecourses extracted
from the right FFA, the right OFA, and the right IFS illustrate that activity
was sustained during the face-processing period (similar activation
timecourses were observed in all face-processing ROIs). The intact
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versus scrambled shape contrast, collapsed over visual field location,
produced activity in occipital–temporal and occipital–parietal regions
including the right and left lateral occipital complex (LOC; see Inline
Supplementary Table S1), while the reverse contrast primarily produced
Fig. 2. Activity associated with faces and shapes. A. Activity associated with faces (in cyan) and objects (in purple) projected onto a cortical surface (key at the top; gyri and sulci are shown
in light and dark gray; inferior and lateral views are shown to the left and right). Face-processing regions-of-interest (ROIs, white circles) consisted of the right and left occipital face area
(ROFA, LOFA), the right and left fusiform face area (RFFA, LFFA), the right and left face-selective region in the superior temporal sulcus (RfSTS, LfSTS), the right and left amygdala (RAmy,
LAmy), the right anterior temporal face patch (RATFP), the right orbital frontal cortex (ROFC), and the right inferior frontal sulcus (RIFS). Face activation timecourses were extracted from
the RFFA, the ROFA, and the RIFS (indicated by the white arrows). Solid vertical lines demarcate face block onset and dotted lines bound the expected period of sustained activity, from 6 s
after face block onset, until face block offset at 14 s. B. Activity associated with intact shapes (in yellow) and scrambled shapes (in green) projected onto a cortical surface (key at the top).
Shape-processing ROIs (black circles) consisted of the right and left lateral occipital complex (RLOC, LLOC). Face-processing ROIs from above (white circles) are also shown. Shape activation timecourses were extracted from the RFFA, the ROFA, and the RIFS (illustrated by the white arrows).
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Table 1
Face-processing ROIs.
ROI
ROFA
LOFA
RFFA
LFFA
RfSTS
LfSTS
RAmy
LAmy
RATFP
ROFC
RIFS
x
y
z
44
−40
38
−37
47
−49
17
−19
35
2
44
−71
−74
−44
−50
−56
−56
−8
−8
−5
37
16
3
3
−18
−18
9
9
−9
−9
−31
−9
27
t-value
8.4
3.1
9.6
5.0
16.1
9.1
9.7
8.3
4.7
8.8
10.6
ROFA = right occipital face area, LOFA = left occipital face area, RFFA = right fusiform face
area, LFFA = left fusiform face area, RfSTS = right face-selective region in the superior
temporal sulcus, LfSTS = left face-selective region in the superior temporal sulcus,
RAmy = right amygdala, LAmy = left amygdala, RATFP = right anterior temporal face
patch, ROFC = right orbital frontal cortex, RIFS = right inferior frontal sulcus.
activity in the posterior–medial occipital cortex (Fig. 2B). Of importance,
activity associated with shapes completely overlapped the right and left
OFA and the right and left FFA (but did not overlap other face-processing
ROIs), which suggests that the OFA and FFA also mediate shape processing. Activation timecourses illustrate that activity was sustained during
the shape-processing period in the right FFA and the right OFA, while
there was little sustained activity in the right IFS.
Inline Supplementary Table S1 can be found online at http://dx.
doi.org/10.1016/j.neuroimage.2013.06.032.
Collapsed activation magnitude comparisons
Fig. 3 shows the magnitudes of sustained activity associated with
faces and shapes, collapsed over visual field location, in all the
face-processing ROIs. As expected, the magnitude of activity associated with faces was significantly greater than 0 in all face-processing
ROIs (all t-values > 6.43, p-values b 0.001). In the right OFA, the left
OFA, the right FFA, the right fSTS, the right ATFP, and the right IFS,
the magnitude of activity associated with shapes was also significantly greater than 0 (right OFA, t = 10.08, p b 0.001; left OFA, t = 5.69,
p b 0.001; right FFA, t = 5.37, p b 0.001; right fSTS, t = 3.28,
p b 0.01; right ATFP, t = 2.00, p b 0.05; right IFS, t = 3.52,
p b 0.01), while the magnitude of activity associated with shapes
was not significantly greater than 0 in the remaining ROIs (left FFA,
t = 1.47, p = 0.085; left fSTS, right Amy, left Amy, right OFC, all
t-values b1). The magnitude of activity associated with faces did not
significantly differ from the magnitude of activity associated with shapes
in the right OFA or the left OFA (right OFA, t b 1; left OFA, t = 2.18, p =
0.052), but the magnitude of activity associated with faces was significantly greater than the magnitude of activity associated with shapes in
all the remaining face-processing ROIs (right FFA, t = 3.65, p b 0.01;
all other t-values >4.48, p-values b 0.001). These results suggest that
the right OFA and the left OFA are similarly involved in face and shape
processing; however, the magnitude of activity associated with faces
was numerically larger than the magnitude of activity associated with
shapes in these ROIs (and approached significance in the left OFA). As
such, these non-significant differences could be attributed to lack of sensitivity. It is also notable that in the right FFA, the magnitude of activity
associated with faces was 2.0 times the magnitude of activity associated
with shapes, which replicates the previous findings reviewed above. The
results considered thus far are consistent with previous findings that
faces produce the greatest magnitude of activity in face-processing ROIs.
Fig. 3. Magnitudes of activity associated with faces and shapes, collapsed across visual field
location, in face-processing ROIs. Each bar illustrates the mean magnitude of activity ±1
standard error (key at the lower right) associated with faces or shapes that were compared
(illustrated by white horizontal lines) within each ROI (***p b 0.001, **p b 0.01, *p b 0.05,
ns = non-significant).
Separated activation magnitude comparisons in the FFA and OFA
Of direct relevance to the hypothesis under investigation, the preceding analysis did not take shape visual field location into account.
Fig. 4 shows the magnitude of activity associated with faces and intact
shapes, separated by visual field location, in all face-processing ROIs
(note that the magnitude of activity associated with faces is identical
S.D. Slotnick, R.C. White / NeuroImage 83 (2013) 408–417
to that shown in Fig. 3). Visual inspection of activity associated with
shapes in the right and left OFA and the right and left FFA revealed
a retinotopic pattern of activity (i.e., left visual field shapes produced
greater activity than right visual field shapes in the right ROIs and vice
versa; cf., Yue et al., 2011), which differed from the pattern of activity
in the other ROIs.
In the right OFA and the right FFA, the magnitude of activity associated with shapes in the left visual field and the central visual field was significantly greater than 0 (right OFA, shape-LVF, t = 16.78, p b 0.001,
shape-CVF, t = 8.42, p b 0.001; right FFA, shape-LVF, t = 4.72,
p b 0.001, shape-CVF, t = 7.72, p b 0.001), while the magnitude of activity associated with shapes in the right visual field was not significantly
greater than 0 in either of these ROIs (both t-values b 1). In the right OFA,
the magnitude of activity associated with faces was significantly smaller
than the magnitude of activity associated with shapes in the left visual
field and the central visual field (shape-LVF, t = 9.54, p b 0.001;
shape-CVF, t = 2.41, p b 0.05), while the magnitude of activity associated with faces was significantly greater than the magnitude of activity associated with shapes in the right visual field (t = 14.37, p b 0.001). In
addition, the magnitude of activity associated with shapes in the left visual field was significantly greater than the magnitude of activity associated with shapes in the central visual field and the right visual field
(shape-CVF, t = 5.55, p b 0.001; shape-RVF, t = 19.30, p b 0.001),
and the magnitude of activity associated with shapes in the central visual
field was significantly greater than the magnitude of activity associated
with shapes in the right visual field (t = 12.90, p b 0.001). Similarly, in
the right FFA, the magnitude of activity associated with faces did not significantly differ from the magnitude of activity associated with shapes in
the left visual field or the central visual field (shape-LVF, t = 1.72, p =
0.11; shape-CVF, t b 1), while the magnitude of activity associated with
faces was significantly greater than the magnitude of activity associated
with shapes in the right visual field (t = 7.43, p b 0.001). In addition,
the magnitude of activity associated with shapes in the left visual field
did not significantly differ from the magnitude of activity associated
with shapes in the central visual field (t = 1.86, p = 0.090), the magnitude of activity associated with shapes in the left visual field was significantly greater than the magnitude of activity associated with shapes in
the right visual field (t = 5.03, p b 0.001), and the magnitude of activity
associated with shapes in the central visual field was significantly greater
than the magnitude of activity associated with shapes in the right visual
field (t = 7.12, p b 0.001). In the left OFA and the left FFA, the magnitude of activity associated with shapes in the left visual field and the central visual field was not significantly greater than 0 (left OFA, shape-LVF,
t b 1, shape-CVF, t = 1.52, p = 0.078; left FFA, shape-LVF, t b 1,
shape-CVF, t = 1.00, p = 0.17), while the magnitude of activity associated with shapes in the right visual field was significantly greater than
0 (left OFA, shape-RVF, t = 19.37, p b 0.001; left FFA, shape-RVF, t =
5.20, p b 0.001). In the left OFA, the magnitude of activity associated
with faces was significantly greater than the magnitude of activity associated with shapes in the left visual field and the central visual field
(shape-LVF, t = 14.54, p b 0.001; shape-CVF, t = 3.42, p b 0.01),
while the magnitude of activity associated with faces was significantly
smaller than the magnitude of activity associated with shapes in the
right visual field (t = 11.00, p b 0.001). In addition, the magnitude of activity associated with shapes in the left visual field was significantly
smaller than the magnitude of activity associated with shapes in the central visual field and the right visual field (shape-CVF, t = 10.95,
p b 0.001; shape-RVF, t = 24.00, p b 0.001), and the magnitude of activity associated with shapes in the central visual field was significantly
smaller than the magnitude of activity associated with shapes in the
right visual field (t = 13.97, p b 0.001). Similarly, in the left FFA, the
magnitude of activity associated with faces was significantly greater
than the magnitude of activity associated with shapes in the left visual
field and the central visual field (shape-LVF, t = 6.79, p b 0.001;
shape-CVF, t = 3.00, p b 0.05), while the magnitude of activity associated with faces did not significantly differ from the magnitude of activity
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associated with shapes in the right visual field (t b 1). In addition, the
magnitude of activity associated with shapes in the left visual field was
significantly smaller than the magnitude of activity associated with
shapes in the central visual field and the right visual field (shape-CVF,
t = 3.17, p b 0.01; shape-RVF, t = 6.14, p b 0.001), and the magnitude
of activity associated with shapes in the central visual field was significantly smaller than the magnitude of activity associated with shapes in
the right visual field (t = 2.77, p b 0.05). It should be highlighted that
in all four of these face-processing ROIs (the right and left OFA and the
right and left FFA), there were instances where the magnitude of activity
associated with shapes was significantly or numerically greater than the
magnitude of activity associated with faces. These findings rule out the
possibility that non-significant differences between the magnitudes of
activity associated with faces and shapes might due to limited sensitivity.
Furthermore, in each of these ROIs, a power analysis of the face versus
shape comparisons revealed there was a large effect size (for all four regions, the maximum Cohen's d value was greater than 1.96; Cohen,
1988).
Shape processing in the FFA and OFA
The preceding results in the right and left OFA and the right and
left FFA suggest that these ROIs are involved in shape processing to
a similar (or a greater) degree than face processing in certain visual
field locations. To evaluate whether these ROIs were involved in processing the visual feature of shape per se, the magnitude of activity
associated with intact shapes was compared to the magnitude of activity associated with scrambled shapes for those visual field locations
that were associated with a similar or greater magnitude of activity
associated with intact shapes than faces (see Fig. 4, top 4 panels).
For the right OFA and the right FFA, the magnitude of activity associated with intact shapes was significantly greater than the magnitude
of activity associated with scrambled shapes in the left visual field
and the central visual field (right OFA, LVF, t = 10.11, p b 0.001,
CVF, t = 9.36, p b 0.001; right FFA, LVF, t = 3.60, p b 0.01, CVF,
t = 6.84, p b 0.001). For the left OFA, the magnitude of activity associated with intact shapes was significantly greater than the magnitude of activity associated with scrambled shapes in the right visual
field (t = 7.04, p b 0.001). However, in the left FFA, the magnitude
of activity associated with intact shapes was not significantly greater
than the magnitude of activity associated with scrambled shapes in
the right visual field (t b 1), which suggests this region is not specialized for processing shape and rather appears to more generally respond to intact or scrambled shapes at this visual field location.
Given that the left FFA was not tuned to shape processing, this region
will not be considered further. The preceding results indicate that the
right and left OFA and the right FFA are involved in processing the visual feature of shape in particular visual field locations.
Separated activation magnitude comparisons in other face-processing
ROIs
For the remaining ROIs, the magnitude of activity associated with
shapes in a given visual field location was sometimes significantly
greater than 0, but never approached the magnitude of activity associated with faces. In the right fSTS, the magnitude of activity associated with shapes in the left visual field and the right visual field was not
significantly greater than 0 (shape-LVF, t b 1; shape-RVF, t = 1.74,
p = 0.055), while the magnitude of activity associated with shapes
in the central visual field was significantly greater than 0 (t = 3.01,
p b 0.01). In the left fSTS, the magnitude of activity associated with
shapes in the left visual field and the central visual field was not significantly greater than 0 (both t-values b1), while the magnitude of
activity associated with shapes in the right visual field was significantly greater than 0 (t = 2.41, p b 0.05). In the right and left amygdala and the right OFC, the magnitude of activity associated with
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Fig. 4. Magnitudes of activity associated with faces and shapes, separated by visual field location, in face-processing ROIs. Each bar illustrates the mean magnitude of activity ±1
standard error (key at the lower right) associated with faces or shapes that were compared (illustrated by white horizontal lines) within each ROI (***p b 0.001, **p b 0.01,
*p b 0.05, ns = non-significant).
S.D. Slotnick, R.C. White / NeuroImage 83 (2013) 408–417
shapes, regardless of visual field location, was not significantly greater than 0 (all t-values b 1). In the right ATFP and the right IFS, the
magnitude of activity associated with shapes in the left visual field
and the central visual field was significantly greater than 0 (right
ATFP, shape-LVF, t = 2.45, p b 0.05, shape-CVF, t = 2.52, p b 0.05;
right IFS, shape-LVF, t = 2.66, p b 0.05, shape-CVF, t = 4.06,
p b 0.001), while the magnitude of activity associated with shapes
in the right visual field was not significantly greater than 0 (both
t-values b 1). In all of these ROIs, the magnitude of activity associated
with faces was significantly greater than the magnitude of activity associated with shapes, regardless of visual field location (right OFC,
shape-CVF, t = 3.77, p b 0.01; all other t-values > 4.74, p-values
b0.001).
Discussion
When we collapsed over visual field location (Fig. 3), the present results replicated previous findings that the magnitude of activity associated with faces is greater than the magnitude of activity associated with
non-face stimuli in the face-processing regions. However, when shapes
were separately analyzed based on their visual field location (Fig. 4) we
found that, for certain visual field locations, shapes produced a greater
or similar magnitude of activity in the OFA and the FFA. Specifically, in
the right OFA, the magnitude of activity associated with shapes in the
left visual field and the central visual field was significantly greater
than the magnitude of activity associated with faces, in the left OFA,
the magnitude of activity associated with shapes in the right visual
field was significantly greater than the magnitude of activity associated
with faces, and in the right FFA – the classic face-processing region – the
magnitude of activity associated with shapes in the left visual field and
the central visual field did not significantly differ from the magnitude of
activity associated with faces (Fig. 4, top 4 panels). The pattern of activity in all face-processing regions other than the OFA and FFA showed
clear face-processing specialization, with the magnitude of activity associated with faces significantly greater than the magnitude of activity
associated with shapes at all visual field locations.
It should be underscored that in 4 instances (i.e., left and central visual field shapes in the right OFA, right visual field shapes in the left
OFA, and central visual field shapes in the right FFA), the magnitude of
activity associated with shapes was significantly or numerically greater
than the magnitude of activity associated with faces in face-processing
regions. The face versus object contrast used to identify these regions
maximized the magnitude of activity associated with faces in these regions. That is, this contrast was statistically biased, thus the magnitude
of FFA activity associated with faces was increased to a relatively greater
degree than the magnitude of activity associated with shapes. Still, the
magnitude of activity associated with shapes associated with certain visual field locations was greater than that associated with faces in the
OFA and the FFA. In a recent fMRI study that employed an individuation
task, a statistically equivalent magnitude of activity was produced in the
OFA and the FFA by faces, objects, and wristwatches (Haist et al., 2010).
However, in that study, the magnitude of activity associated with faces
in the FFA was numerically greater than that produced by the other
item types, which could be attributed to a lack of sensitivity. As such,
the present results are the first, to our knowledge, to report numerically
greater non-face than face activation of the FFA (and significantly greater non-face than face activation of the OFA).
The present pattern of activity in the right and left OFA and the right
FFA indicates that these regions are involved in processing the visual
feature of shape in particular regions of the visual field (i.e., the contralateral visual field in all 3 regions and the central visual field in the right
OFA and the right FFA). Of importance, the magnitude of activation in
these regions was significantly greater during intact than scrambled
shape processing, which ensures that they are involved in processing
shape (given that these stimulus types primarily differ on this feature
dimension). As the right FFA appears to be tuned to shape processing,
415
this could provide a partial mechanism for the response of this region
to both faces and non-face items given that both types of stimuli can
be defined by a shape delineating the outer boundary and shapes detailing internal features.
One limitation of the present study is that the face localizer and the
shape localizer constituted separate runs, which might have introduced
differences that precluded activation magnitude comparisons. A metaanalysis was conducted to estimate the degree to which the present
magnitude of activity associated with faces in the FFA (during the face
localizer) and the present magnitude of activity associated with shapes
in the LOC (during the shape localizer) were reduced as compared to
previous studies that employed face localizers (Gilaie-Dotan et al.,
2008; Grill-Spector et al., 2004; Kanwisher et al., 1997, 1998, 1999;
Tong et al., 2000; Tsao et al., 2008) and shape/object localizers (Amedi
et al., 2001, 2002; Avidan et al., 2002; Grill-Spector, 2003; Kourtzi and
Kanwisher, 2000; Lerner et al., 2002; Yin et al., 2002). These relative reductions in activation magnitude were due to the absence of a rest period between blocks in the present study (e.g., the magnitude of
activity associated with faces in the FFA did not return to baseline due
to activation of this region during object blocks). Critically, as compared
to previous studies, the present magnitude of activity associated with
faces in the FFA and the present magnitude of activity associated with
shapes in the LOC were reduced to a similar degree (0.15–0.19 times),
which supports the current comparisons between the magnitudes of
activity associated with faces and shapes. It is also possible that differences in the localizer stimulus protocols (i.e., the number of stimuli
within each block, the relative novelty of the shapes, the size of the
stimuli, and the number of blocks) might have produced different levels
of power, which, if true, would question the validity of comparing face
and shape activation magnitudes. However, the number of stimuli
within each face block (10 stimuli) or shape block (14 stimuli) would
not be expected to produce differences in power as it can be assumed
that the corresponding cognitive process (i.e., face perception or
shape perception) was maintained for the entire 14 s duration of each
block. To evaluate whether shape novelty might have been a factor, a
meta-analysis was conducted to compare the magnitude of activity in
the LOC associated with shapes (Grill-Spector, 2003; Kourtzi and
Kanwisher, 2000) and familiar objects (Amedi et al., 2001, 2002;
Avidan et al., 2002; Lerner et al., 2002; Yin et al., 2002). The magnitude
of activity associated with shapes (mean 1.35% signal change) was less
than that associated with objects (mean 2.14% signal change), which indicates the high magnitude of activity associated with shapes in the FFA
was not due to stimulus novelty. To determine whether different stimulus size or number of blocks in the face localizer and the shape localizer
could have influenced the results, we conducted a meta-analysis of face
localizer and shape/object localizer studies (Avidan et al., 2002;
Grill-Spector et al., 2004; Kanwisher et al., 1997, 1998, 1999; Lerner et
al., 2002; Tsao et al., 2008; Yin et al., 2002). There was no significant correlation between stimulus size (range 3.5–18°, mean 11.44° of visual
angle) or number of blocks (range 2–8, mean 4.75) and the magnitude
of activity associated with faces or shapes/objects (both p-values
>0.20), which indicates these factors did not produce differences in
power. More generally, the present study was limited in that it had an
intermediate number of participants. A final design limitation of the
present study was that faces were not presented in different visual
field locations. This prevented testing whether face processing, like
shape processing, was modulated by visual field location (e.g., using
an ANOVA approach). The preceding limitations are topics for future
research.
Perhaps due to the fact that faces are symmetrical, which may
have driven visual field/hemispheric specialization to maximize processing efficiency (cf., Kosslyn, 1987), there is a left visual field bias
during face processing (for a review, see Yovel et al., 2008). By comparison, non-face items, such as objects, are typically asymmetrical
and thus need to be processed in both the left and right visual fields
(it can also be assumed that both faces and non-face items require
416
S.D. Slotnick, R.C. White / NeuroImage 83 (2013) 408–417
central visual field processing). By this account, the right FFA may be
particularly responsive to faces because such stimuli are composed of
many salient shapes that are primarily processed in the left and central visual fields, while the FFA response to objects may typically be
muted due to the addition of shape processing in the right visual
field (e.g., Fig. 4, in the right FFA panel, the addition of shape-right visual field activity, which is negative in magnitude, to shape-left visual
field and shape-central visual field activity would diminish the overall
response to non-face items).
Attention may also play a role in face and non-face item processing
given this process is known to amplify the magnitude of activity in visual sensory regions, including the right FFA (Serences et al., 2004; Xu et
al., 2012). The response of the right FFA to faces may be modulated by
attention toward the shapes that comprise a face such as the external
contour and the shapes of the internal features such as the eyes and
the mouth. As faces are composed of a relatively high number of shapes
and face processing requires a relatively high degree of attention to this
feature, faces would be expected to produce a more robust response in
the right FFA than non-face items such as objects, cars, and houses (as
has been reported in all previous studies). However, in the present
study, abstract shape processing in the left and central visual fields produced activity that was equivalent in magnitude to that of faces without
a task that required attention to the feature of shape (or identity; see
Haist et al., 2010). This suggests, at least in the current paradigm, that
attention played a smaller role in modulating activity in the FFA than
the left visual field hemispheric processing bias discussed above. Future
research will be required to disentangle these processes during different stimulus and task conditions.
It should also be mentioned that the current analysis focused on
the mean magnitude of activity in a given face-processing region.
An alternative method of analysis is based on the pattern of activity
across voxels in a region, referred to as multi-voxel pattern analysis
(MVPA). A recent MVPA study revealed that voxels throughout the
FFA were sensitive to faces, animals, cars, and sculptures (Hanson
and Schmidt, 2011). Based on the present findings, we predict that
an MVPA analysis of the right FFA will reveal equivalent sensitivity
to faces and shapes in the left and central (but not right) visual fields.
This is a topic of future research.
The present results indicate that the right FFA is tuned to shape
processing in the left and central visual fields, which is at odds with
the widespread belief that this region is selective for the holistic processing of faces. Moreover, we observed activity associated with faces
in 11 different regions, which questions whether face processing is in
any way localizable to the right FFA and supports the view that face
processing, like the processing of other visual stimulus classes, is mediated by distributed and overlapping brain regions (Haxby et al.,
2001; Ishai et al., 1999, 2000). Therefore, given that this particular region of the ‘fusiform’ cortex is neither selective for ‘face’ processing
nor is face processing restricted to a single ‘area’ or even a few
areas, there seems to be little if any basis for labeling this region the
fusiform face area (Slotnick, 2013).
Acknowledgments
This work was supported in part by NSF grant BCS-0745880.
Conflict of interest
The authors report no conflicts of interest.
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