Article Figures & Data
Figures
- Figure 1.
The stimulus design. a, The stimulus consisted of four sinusoidal grating patches placed in the periphery (6.4°) of the four quadrants. b, Left, The temporal structure of the stimulus in the test blocks. The gray solid and dashed curves depict the time courses of the contrast modulation in the surround in two different phase conditions (phase A: sine [0°]; phase B: negative cosine [−90°]), and the black curve represents the difference of the two phases. The modulation period, T, was either 40 s (subject 2) or 48 s (subjects 1 and 3). Right, Snapshots illustrating the stimulus appearance when the contrast in the surround changed from high (100%) to low (20%). The contrast of the center grating was fixed at 100% in the HCC condition and 20% in the LCC condition.
- Figure 2.
The effects of contextual surround on cortical responses. a–c, Voxel- and block-averaged BOLD responses in the HCC condition from a representative subject (subject 1). a, The average differential response of voxels in the center region (black curve), which was the difference between the two original responses obtained in phase A (gray solid curve) and phase B (gray dashed curve). b, The responses of voxels in the surround. The two black curves in a and b are overlaid in c. The red solid and orange dotted curves are the sine wave fits to the differential responses in the center and surround, respectively. d–f, Similar results as shown in a–c, but for the LCC condition. g, The modulation amplitudes obtained from all three subjects. The blue and red bars are respectively for HCC and LCC conditions. The filled bars indicate the responses in the center and the open bars show the responses in the surround (excluding the center region). The bar length reflects the average of corrected modulation amplitudes from the sine wave fits and the polarity of a bar indicates whether the modulation was positively or negatively correlated with the contrast modulation in the surround (see Materials and Methods). h, i, Correlations between the responses in the center and surround in HCC (h) and LCC (i) conditions from subject 1. The time points were sampled from the duration of the test blocks, taking the hemodynamic response delay (6.06 s or 3 TRs) into consideration. The gray line in each plot is the result of the linear regression. j, The modulation ratios, defined by the slope of the linear regression shown in h or i, for the three subjects. The blue and red bars represent the modulation ratios in HCC and LCC conditions, respectively. A negative modulation ratio indicates that the contrast modulation in the surround had a suppressive effect on responses of voxels in the center region.
- Figure 3.
Voxel by voxel analysis of the surround effects. a, b, The resultant sinusoidal fitting and clustering analysis for the high-center-contrast condition. a, Voxelwise responses in the center (black traces) and surround (gray traces) for a representative subject (subject 1). b, Two histograms displaying the difference between the phase of the fitted curve of a single voxel and the mean phase of fitted curves of all voxels in the surround (θ̄S) for the voxels in the center region (black bars) and the voxels in the surround (gray bars), respectively. The data from three subjects are pooled. The black and gray arrows indicate the mean phase differences of the voxels in the center and surround, respectively. For reference, the mean phase for the voxels in the surround is adjusted to zero phase. The two histograms depict largely separable clusters of the voxels in the center and surround. c, d, The results for the low-center-contrast condition. The conventions are the same as in a and b. Note that the clusters in the center and surround are almost inseparable in this condition.
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Supplemental Data
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