The decomposition of image motion
Theories about how image motion can be processed by the visual system rest on one simple mathematical fact: image motion can be decomposed linearly into traveling sinusoidal waves, just like static images can be decomposed into static sinusoidal patterns. The point was most famously made by the classic paper "Model of human visual-motion sensing" by Watson & Ahumada (1985). The consequence is that any system that can deal with traveling waves can deal with motion. All that is required is some linear operations (with minimal nonlinearity throw in). While the idea is very simple, sometimes I find it difficult to explain it to students. I have therefore developed a demonstration to show that it can actually be done. It is written in Mathematica.