While looking through articles for a class assignment, I fell upon this article. Professors from Rutgers and University of Penn came together to test "One long-time hypothesis is that the brain segments scenes into different regions of illumination and then uses ratio coding to decide what looks white."
In short, they used a 5 by 5 checker board with gray scale squares. The participant was to match the square to where it falls on the gray scale. "“This research is important because we have falsified the ratio hypothesis, which is currently the most widely invoked explanation of how we perceive lightness,” Allred says. “We also were able to reject several similar models of lightness. We were able to do this because we measured lightness in such high-range and relatively complex images.”"
This is fascinating because we discussed in class how we can tell a wall with a shadow is still the continuation of a color. These researchers are on the way to discovering why that is.