Fig. 6.

Orientation tuning of VSDI signal. A: image of the cortical vasculature; V1/V2 border is parallel to the top of the image. B: spatial 1-D amplitude spectrum of the single-orientation response maps. The 2-D amplitude spectrum of each map was averaged radially and then averaged across the 12 orientations. The peak at 1.2 cycles/mm is due to orientation columns with a corresponding peak period of ∼0.83 mm. C: average response maps to 4 of 12 orientations. Only the components with spatial frequency between 0.8 and 3 cycles/mm, indicated by the shaded area between the dashed vertical lines in B, are shown. The spatial filtration removes components with periods larger than 1.25 mm and smaller than 0.33 mm. D: orientation map computed on the basis of the vector sum of the responses. Hue represents preferred orientation, and saturation represents tuning amplitude. The white square corresponds to the magnified region (0.7 × 0.7 mm²) inset at right. E: correlations between all pairs of response maps as a function of the orientation difference. Different colors indicate different ranges of spatial filtration. Adding lower or higher spatial frequencies causes the correlation functions to flatten, suggesting that the added frequencies contribute components that are less orientation selective. F: normalized VSDI orientation tuning curve including the untuned component. Different colors indicate different ranges of spatial filtration. In E and F, SE values are smaller than symbols.