Stimulation procedure
Stimulation during the experimental runs consisted of 16 stimulus blocks, with
four blocks for each condition. The total time of each experimental run was 592 s,
including pre-, post-, and inter-stimulus rest periods of 18 s, and a stimulation period of
18 s. Each stimulation block had 12 stimulus trials, which comprised 1.5 s on and 1.5 s
off periods (Supplementary Fig. 1b). Four stimulus blocks were randomly repeated for
each stimulus condition. Each rest period consisted of 12 red or green crosshairs of 1.5 s.
Red and green crosshairs appeared randomly during the stimulation blocks and rest
periods. During scanning, subjects were instructed to focus on the crosshair at the
center of the screen and to press two buttons (button 1 for green and button 2 for red)
when the crosshairs changed color. The pictures occupied 9  11 degrees for faces and
13.5  10.5 degrees for buildings, while the border of the pictures to the center was 3
degrees off along the horizontal axis from the center of the subject’s visual field. The
crosshair was 1.5  1.5 degrees.
Visual stimulation
Visual stimuli were presented in the first experiment using a projector
(Panasonic Corporation, Osaka, Japan; spatial resolution 1024  768 pixels; refresh rate,
60 Hz) onto a mirror mounted onto a head coil. The pictures occupied 9  11 degrees for
faces and 13.5  10.5 degrees for buildings, while the border of the pictures to the center
was 3 degrees off along the horizontal axis from the center of the subject’s visual field.
The crosshair was 1.5  1.5 degrees. The upright and inverted face pictures used in the
second experiment were presented at the same visual angle and position as those in the
first experiments. All pictures were grayscale images, and the background was black.
Analysis of imaging data
(Region of interest analysis)
Three regions of interest (ROIs) were investigated in the right hemisphere.
V1 was identified based on the contrast of the contralateral and ipsilateral responses.
Voxels were determined as V1 if they were located around the calcarine sulcus and
above a significance threshold (p = 0.0001, corrected). The V1 region is distinctly off-set
from the V1 when activated by a stimulus in the central visual field. The OFA and FFA
were identified based on the contrast of the face and building responses. Voxels located
around the lateral occipital gyrus and significantly above a threshold (p = 0.001,
uncorrected) were determined as OFA. Voxels located in the fusiform area and
significantly above a threshold (p = 0.001, uncorrected) were determined as the FFA.
(Group analysis)
For ROI analysis, each averaged response was extracted from the V1, OFA, and
FFA in the right hemisphere. For each area, a maximum of 40 voxels with p < 0.001 (the
contrast of the left to the right responses for V1 and the contrast of the face to building
responses for the OFA and FFA; uncorrected) were extracted from each ROI.
The SPSS statistical package (SPSS Inc., Chicago, IL, USA) was used for statistical
evaluations. Response differences across the areas of the V1, OFA, and FFA were tested
using a two-way analysis of variance with the “region * condition.” The region factor had
three levels, i.e., the V1, OFA, and FFA, while the stimulus condition factor had two
levels, i.e., the left and right. The dependent variable was the percent signal change
estimated for each stimulus condition at each ROI.
(Analysis procedure)
Analyses were performed as follows: identification of face areas, the evaluation
of response differences in the ipsilateral and contralateral areas, and the determination
of response dominance (ipsilateral-response dominance or contralateral-response
dominance). The distribution of the response dominance in the OFA and FFA was tested
at the individual voxel level. Histograms and distribution maps of the RCI values in the
FFA were produced for each subject. The validity of the RCI values was verified by
evaluating the test-retest reliability. For this, purpose, six pairs of ipsilateral and
contralateral responses were evaluated for each voxel. There were four event-blocks
each for the ipsilateral and contralateral stimulation. One event-block was selected
from each four event-blocks of ipsilateral and contralateral stimulation using a “four
choose one” method. Responses were averaged in the two event-blocks. The averaged
responses to ipsilateral and contralateral stimulation produced four pairs per voxel. The
RCI of the four pairs was calculated for each voxel, and the percentage of repetition of
the same sign (ipsilateral-dominant/contralateral-dominant: −/+) was evaluated. A voxel
was regarded as significantly repeating the sign if three out of four pairs had the same
sign. The percentage of voxels in the FFA that significantly repeated the sign was
evaluated for each subject.
In the second experiment, the data, which showed ipsilateral voxels above the
mean in the first experiment, were evaluated to test the functional role depending on
the response dominance of voxels. The functional roles of the FFA were evaluated for
each response by ipsilateral- and contralateral dominant voxels.