Mueller-Lyer illusion

The Mueller-Lyer illusion is a famous distortion optical illusion consisting of nothing more than an arrow. When viewers are asked to place a mark on the figure at the mid-point, they invariably place it more towards the "tail" end.

Another variation consists of two arrow-like figures, one with both ends pointing in, and the other with both ends pointing out. When asked to judge the lengths of the two lines, which are equal, viewers will typically claim that the inward pointing pair is longer.

Possible Explanations

One possible explanation is that one sees the lines as 3 dimensional, such as the outgoing and ingoing corners of a room:

Another possible explanation is that the line with arrows pointing inwards may simply appear longer because the arrows themselves extend past the line.

External links

• Müller-Lyer
• Explanation of the Mueller-Lyer, Ebbinghaus, and Delboef illusions, and other gestalt effects