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counted as active for each 3-D anatomical image. Because the voxel size is 1 × 1× 1
mm, the active voxel volume in the V1 for each eccentricity condition equals the
counted number of voxels. If we assume that cortical thickness was invariable in the
V1, then the V1 surface area can be obtained by dividing the voxel volume by the
cortical thickness, assumed here to be 2.5 mm^2.
3 Results
3.1 Eccentricity Maps
Figure 1 shows a three-dimensional rendering of the left hemisphere of subject LS.
The surface represents the boundary between white and gray matter that was identi-
fied by segmentation algorithm [11]. Within this portion of the brain, each cortical
region responds mainly to a visual stimulus at one retinotopic location.
Figure 1A shows a color map of the response to an expanding ring on a medial
view of the cortical surface, which indicates the eccentricity (distance from the fovea)
that causes a signal at that location. The hue of the color at each cortical surface point
indicates the response phase, which is proportional to the eccentricity of the local
visual field representation. The data in this figure represent the average of three sepa-
rate sessions. In Figure 1B, the cortical surface was unfolded, which is processed by
inflation algorithm. In Figure 1C, the surface region including the occipital lobe, pos-
terior parts of the parietal lobe and temporal lobe, containing the activated area has
been cut off, and the resulting approximately conical surface cut again along the fun-
dus of the calcarine sulcus to allow it to be flattened completely.
There is a systematic increase in eccentricity moving anteriorly along the medial
wall of occipital cortex. As the expanding ring stimulus moved from the fovea to the
periphery of the retina, the location of the responding areas varied from posterior to
anterior portions of the calcarine sulcus in what is referred to as the eccentricity di-
mension of retinotopic. The larger peripheral representation crossed to the fundus of
the parieto-occipital sulcus.
A parallel treatment of data from the rotating hemifield stimulus is shown in Fig-
ure1. The color also indicates the phase of the periodic response, which is now pro-
portional to the polar angle of the local visual field representation. The locations of
several visual areas were identified by measuring angular visual field representations
[12, 13]. Figure 1d shows the angular visual field representations on the folded and
unfolded surface that spans most of the occipital lobe and posterior parts of the parie-
tal lobe and temporal lobe. The color at each location represents the angle of the rotat-
ing wedge that caused an fMRI response.
3.2 The Sizes of V1/V2/V3
Table 1 contains measurements of the surface area of the visual field representations
from 0-60 deg. Right and left hemispheres, (left and right visual field) as well as dor-
sal and ventral aspects (lower and upper visual field) are listed separately for each
subject. Figure 2 shows the correlation in size between V2 and V3 is significant
