You’ve seen this illusion before, right?
The “grid” defining the light gray squares on the left side of this figure seems to get lighter where the lines intersect. The graph on the right shows that the actual reflectance (or brightness when depicted on a computer screen) of the figure does not change along the path marked by the blue line. But perceived brightness (indicated in red on the graph) does change.
But what’s really interesting about this graph is that the thing doing the perceiving isn’t a human. It’s an artificial neural network. Auntie Em has the details:
The brain in question was an artificial neural network (ANN) that only ever existed inside a computer. It was trained to successfully perform on a lightness constancy task. Most excitingly, when trained to discern between overlapping layers, the ANN sees White’s illusion (Box E). White’s illusion has been problematic to model as the lightness perception goes “the other way” from the stimuli shown here. Thus, the by-product of learning to see lightness and depth is a susceptibility to these illusions. This also tells us something about how animal brains, including our own, work.
Here’s that panel showing White’s illusion:
Fascinating, isn’t it? You can read the entire study, free, on PLoS.