GC analysis of V4 feedback modulations based on spike trains. (A) Influences of V4 on V1 contour sites with (solid lines) and without (dashed lines) the influences from V1 background sites for different contour lengths. (B) Data shown in A are replotted here, showing the overall GC (summed over 0–50 Hz, left y axis) as a function of contour length with (solid black curve) and without (dashed back curve) the influences from V1 background sites. The gray curve (associated with the right y axis) represents percentage reductions (Friedman test, all Ps < 0.001) in GC after discounting the influences from V1 background sites. Error bars represent ±SEM. (C and D) Similar to A and B, but showing the influences of V4 on V1 background sites with and without the influences from V1 contour sites (Friedman test, all Ps < 0.001). A similar analysis based on LFP data is shown in Fig. S3.