Contrast response functions for different adaptation levels and in different visual areas. The top row of A, B and C show contrast response functions constructed as detailed in the text for voxels in retiontopically defined V1, V2 and V3 and averaged over all subjects. The bottom three rows show distributions of parameters of fits of contrast response functions performed on a voxel by voxel basis, where the second, third and fourth rows are the distribution of parameters for c50, Rmax and offset, respectively (see text for details). Arrows indicate mean values of distributions. As detailed in the text, 0% BOLD is set to the mean response during the baseline period of the experiment.