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Optical illusion

Answer

Cafe wall

Are these lines straight and parallel?

Try holding a straight edge against them. Professor Richard Gregory and members of his lab spotted this illusion whilst walking past a café in Bristol, UK.

The so-called “café wall” comprises a rectangle divided horizontally by 4 grey lines. Between each adjacent pair of lines the area is divided vertically into alternate black and white rectangles. The black and white pattern of the top, middle and bottom rows align, but the pattern of black and white rectangles in the second and fourth rows are shifted very slightly to the right. This gives to false impression that the lines that separate the five rows are neither straight nor parallel. In fact they are, but the horizontal grey between the white and the black rectangles is less clear so the continuity and aspect of these horizontal grey lines is confusing to look at.

For a description of the image place your cursor over it (certain browsers only), or click here for an audio transcript.

Answer

Did you know?

Eating brocoli, spinach and other similar vegetables regularly can help prevent eye disease. Find out more