For today, much of what we have been hearing about is context, context in perception. Neuroscientist are usually interested in is how context affects what we see. But today I am going to focus on the question of why context matters. The effect of context is fundamental to everything that the brain does even what is most basic to the brain … seeing colour. One of the examples I am going to show here is a well known color contrast illusion vision. As a neuroscientist I get very excited about very simple effects and why this comes about.