Do any lines feel longer or shorter?

A cream and yellow exhibit table and headboard with the title 'do any lines feel longer or shorter?'. on the table top is a yellow and black board with metal lines that have arrows, no arrows or perpendicular lines on each line length.

Judgement of line length can be influenced through this Müller-Lyer line illusion.

How it works

This is a tactile version of the Müller-Lyer line illusion. Close your eyes and feel six different raised lines on the board. 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).

Things to try or ask around the exhibit

Do you ‘see’ with your fingers as well as you can see with your eyes?

Background

Humans are very dependent on vision. In the well-known Müller-Lyer illusion, the lines are the same length, but the arrowheads make the lines appear longer or shorter, possibly due to how your brain processes size constancy. Your brain uses size constancy to calculate the size of a shape, based on the image that the shape projects onto your retina, as well as how far away (or nearby) your brain believes the shape to be.

We can also rely on our sense of touch when we are trying to work out the size and shape of things. People who have a vision impairment, 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.

Finding the science in your world

The interior corner of a room and the exterior corner of a building are similar to the Müller-Lyer lines, where the arrowhead fins point outwards or inwards respectively at the corner of a room or the corner of a building. Your brain's familiarisation with these lines may be part of the reason why the Müller-Lyer illusion works.