Before revision:  Previous works showed that they act simultaneously, and can produce larger shifts in color matching when acting in synergy with a spatial pattern. At some point in an image, the color perceptually seems more similar to that of the adjacent locations , while being more dissimilar from that of remote neighbors.
After revision:  They have been previously shown to act synergistically, so that at some point in an image, the color perceptually seems more similar to that of the adjacent locations , while being more dissimilar from that of remote neighbors.