When you use this hands-on exhibit…you’ll close your eyes and feel six different lines. Even though all of the lines are the same length, some will feel longer or shorter than others (similar to when you simply look at the lines).
Humans are very dependent on vision, but we can also rely on our sense of touch when we are trying to work out the size and shape of things.
Vision impaired people, including people who have been blind since birth, have also experienced the Müller-Lyer line illusion when they feel the lines. Scientists aren’t sure why this is the case, but they continue to research the visual and tactile version of the illusion.
Maybe when you feel the Müller-Lyer lines with your eyes closed, your brain is interpreting the straight edges like the corners of a box?
These well-known visual illusion lines are all the same length.
The arrowheads make the lines appear longer or shorter, possibly due to how your brain processes size constancy and is used to the straight parallel lines of urban roads and buildings.
For example, the interior corner of room is similar to the lines where the arrowhead fins point outwards. The exterior corner of a building is similar to the lines with arrowhead fins pointing inwards.
Size-constancy is how your brain calculates the size of a shape, based on the size of the image it projects onto your retina, as well as how far away (or nearby) your brain believes the object to be.