Patrick Cavanagh in Nature:
Although we rarely confuse a painting for the scene it presents, we are often taken in by the vividness of the lighting and the three-dimensional (3D) layout it captures. This is not surprising for a photorealistic painting, but even very abstract paintings can convey a striking sense of space and light, despite remarkable deviations from realism.
The rules of physics that apply in a real scene are optional in a painting; they can be obeyed or ignored at the discretion of the artist to further the painting’s intended effect. Some deviations, such as Picasso’s skewed faces or the wildly coloured shadows in the works of Matisse and other Impressionists of the Fauvist school, are meant to be noticed as part of the style and message of the painting. There is, however, an ‘alternative physics’ operating in many paintings that few of us ever notice but which is just as improbable. These transgressions of standard physics — impossible shadows, colours, reflections or contours — often pass unnoticed by the viewer and do not interfere with the viewer’s understanding of the scene. This is what makes them discoveries of neuroscience. Because we do not notice them, they reveal that our visual brain uses a simpler, reduced physics to understand the world. Artists use this alternative physics because these particular deviations from true physics do not matter to the viewer: the artist can take shortcuts, presenting cues more economically, and arranging surfaces and lights to suit the message of the piece rather than the requirements of the physical world.
In discovering these shortcuts artists act as research neuroscientists, and there is a great deal to be learned from tracking down their discoveries.
More here.