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Flat Maps
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As stated in chapter 2, area V1 of each hemisphere represents an entire hemifield. For the ro-
tating wedge stimulus, the theoretical range of phases within V1 has a width of . The other
half of the phase spectrum can be found in the other hemisphere. In contrast, V2v represents
only the upper quarter visual field, and V2d represents the lower quarter. Therefore, the theo-
retical range of phases within V2v has a width of /2.
3.8.2 Coherence Maps
In addition to phase maps, mrFindBorders calculates a measure of coherence to create coher-
ence maps. The coherence between the fMRI time signals and the stimulus signal is calculated
by dividing the power at stimulus frequency (stimulus alternation frequency, e.g., 1/36 Hz) by
the total power: coherence = s/(s+n), where s is the power at stimulus frequency, and n is the
noise (power at frequencies other than the stimulus frequency). This measure of coherence can
therefore be seen as a normalized power. Time signals from cortical areas that show activation
caused by the stimulus will have a high coherence value.
Flat maps of coherence values are created in a similar way as the phase maps: The coher-
ence is calculated for the voxels in the vAnatomy-3D coordinate system. Then, the data is pro-
jected onto a flat map by using the mapping provided by mrFlatMesh. The coherence maps
can be used to threshold the phase data. If a certain pixel in the flat map has a coherence value
that is below the threshold, then the phase value at this location is not used for further calcula-
tion.
3.8.3 Visual Field Sign Maps
As explained before, the traveling waves that are created by a rotating-wedge visual stimulus
travel in opposite directions in adjacent visual areas because the orientation of the cortical
map is different for adjacent visual areas. The orientation of the cortical map can be deter-
mined by a visual field sign map [Sereno, et al., 1994 #43]. In mrFindBorders, a visual field
sign map is calculated from retinotopic data by determining the cross product between the
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