The Cafe Wall Illusion

Back at the end of the 1970s, when I was finishing my PhD at Bristol University, the exterior of a cafe close to the university had a black and white tile decoration that gave the illusion of being distorted from the true. One of Professor Richard Gregory's research team spotted it, and it became the subject of a famous paper, Border Locking and the Cafe Wall Illusion.

Just recently, I noticed that a local barbershop had been given a makeover, which included tiling that nicely shows the wedge distortion of the cafe wall illusion:




In their paper, Gregory et al described experiments which locked down the parameters that evoked the illusion, and proposed a model, border-locking theory, that suggested the functional mechanisms in the human eye that generated it. A nice example of how observation of something unusual in the everyday and close examination and dissection of what it is and how it works can uncover an underlying fundamental truth. Science in action!