Do we have the original data (the raw) in here somewhere? It would help to confirm your stats - some of the above assumes RT is the one doing something different, but it could also be the one not doing something. Some of the graphs have scales which makes differences appear larger, perhaps enough that quantization in your tiff could play a part?
Taking a 3x3 patch standard score your tiff shows this (first channel, obviously I added grid):
Looks like something periodic happening and not exactly aligned with your 200x200 grid (need to click and view full image to see that properly).