Figure 3. Axial anisotropy in CPS. A, B, Example time courses and fPSFs from area V1 of a single subject. A, Pairs of averaged time courses of fMRI responses, including one from the coaxial (black) condition and one from the ortho-axial (gray) condition, shown as sample eccentricity bins. The gray vertical bars indicate the peak zones of frames (see Materials and Methods for definition). From the trial-by-trial distribution of fMRI responses in this zone for each eccentricity bin, the mean amplitudes (the circle symbols), and 95% confidence intervals (the lines behind the circle symbols) were estimated. The black horizontal bars at the bottom of each panel demarcate the 9 s stimulus-on period. B, Comparison of the coaxial and ortho-axial fPSFs. The thin jagged lines are the fPSFs, which consisted of sliding-window averages of response amplitudes within eccentricity bins. The translucent patches represent the bootstrap 95% confidence interval of those averages. The small circles are the average response amplitudes for the eccentricity bins that were sampled in A. The thick smooth curves are the DoG models fit to the observed fPSFs. The hyphenated lines indicate the spatial extents of the positive portions of the model fPSFs. The two different brightness levels of the lines, symbols, and patches indicate the axiality conditions (black for the coaxial condition and gray for the ortho-axial condition). C, D, Population analysis of axial anisotropy. Symbols and brightness levels represent subjects and visual areas, respectively. C, Scatter plot of the spatial extent estimates from the ortho-axial condition (Eo) relative to estimates from the coaxial condition (Ec). The error bars are bootstrap 95% confidence intervals. D, A stacked histogram of axial anisotropy indexes (AIAXs). The downward triangles of different brightness levels mark the median AIAX values for different visual areas and the white arrow on the x-axis marks the grand median AIAX across three visual areas. The asterisk above the arrow indicates that the AIAX values are significantly different (p < 0.05) than zero.