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RetroScience: Can You Spot The Illusion?

Want to travel back in time? In our weekly “Retro Science” series, we’re digging up visual artifacts that capture fascinating moments from science history, including surprising studies, outdated inventions, and breakthrough achievements. By recapturing science’s impressive feats and most amusing flops, RetroScience will remind us of how far we’ve come, and how far we have yet to go.


Psychologist Richard Langton Gregory Revisits The Café Wall, An Optical Illusion Studied In 1973.

If you think those tiles are tilting, your brain is fooling you– they are perfectly aligned.

In 1973, British psychologist Richard Langton Gregory studied this very illusion after a colleague spotted it on the wall of a café across the street from their laboratory. Gregory was the first to successfully deconstruct the illusion, now known as the Café Wall Illusion. He described the pattern as a ‘brick’ and ‘mortar’ design in which black and white ‘brick’ tiles were stacked between gray ‘mortar’ lines. The titling illusion only occurred when the mortar lines were darker than the brightest tile and lighter than the darkest tile. He proved this by showing two alternate versions of the pattern, with the mortar in white, then in black. As seen below, only the pattern in with gray mortar lines shows a strong tilting illusion (center figure). To learn more about the Café Wall Illusion, see Dr. Gregory’s full study here.


The Café Wall display, showing the basic effect of change of luminance of the mortar lines. The tilting illusion only works when the mortar lines are gray (not lighter than the white tile and not darker than the black tile). Figure taken from

Gregory performed many studies on optical illusions and what they revealed about human perception, publishing several books on the topic including Eye and Brain and Mind in Science. Like ophthalmologist Geoff Tabin, Dr. Gregory witnessed the miracle of the blind regaining eyesight. In 1958, Gregory made discoveries in optical and cognitive research by studying Sidney Branford, a man who restored his sight after 52 years of blindness through a cornea transplant. See Dr. Gregory describe Branford’s first experience of sight here. When he was not doing research, Gregory made frequent television appearances and had an eye for making puns (ha!). Gregory passed away at age 86 in May 17, 2010.




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Jaime Sunwoo

    Jaime Sunwoo is the digital media intern of the Secret Life Blog. She is currently a senior at Yale University. When she’s in the lab, her secret is that she makes art and when she’s in art class, her secret is that she enjoys science research. Sometimes she combines both interests, making fungal sculptures and botanical drawings. She enjoys learning about scientists and how their varying interests can lead to interdisciplinary work.