The Müller-Lyer Illusion

In the Müller-Lyer Illusion, three lines are shown with arrows pointing inwards or outwards at both ends of the line. When we look at these arrows (in the top picture) and try to figure out their lengths, the line in the middle seems to be longest, followed by the third line, and the first line is the smallest. However, this is not true. All of the shafts of the lines are actually the same exact size, as the bottom picture shows.

This is a popular illusion that has been the subject of various theories and psychological experiments. However, there does seem to be a neurological basis to this illusion. This illusion occurs because our brain is used to perceiving depth in the 3D world. When the brain must switch to a 2D view of this image, it perceives the image as 3D. This makes the brain think that the shafts of the lines are different sizes, as the size constancy mechanism does not function the same for 2D images as it does for 3D images. Another simpler explanation is that since the lengths of the lines including the fins of the arrows is different, the brain automatically thinks the lengths of the shafts are different.

This optical illusion teaches us that the visual system can be easily tricked, and it does not perceive 2D and 3D images the same way.

Interestingly, it has been shown that the perception of this illusion varies between cultures and age groups.

2 responses to “The Müller-Lyer Illusion”

  1. Hannah Bukzin says:

    I love this illusion! I remember seeing this when I was really little and always thought it was fascinating. Its really interesting to hear the neural basis behind it.

  2. Aiswarya Nagasubramony says:

    Very cool illusion. It is interesting to see the science behind how the brain perceives this illusion.

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