The original Müller-Lyer illusion is an 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, we often blogged about 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 often equal, viewers will typically claim that the line with outward pointing arrows is longer. One possible explanation is that one sees the lines as three-dimensional, such as the outgoing and ingoing corners of a room. Another possible explanation is that the line with arrows pointing outwards may simply appear longer because the arrows themselves extend past the line. The other explanation could be simply because outward pointing arrows subliminally suggest that the line is growing.
In the example above, we used exactly the same surrounding suggested. In the Ticket Window Example, both arrows represent outgoing and ingoing corners of a room. It’s almost obvious that the ingoing corner’s arrow is much longer than the other. But look what happens if we fade the background and leave the arrows untouched. Shamefully, this didn’t make any difference. The right arrow still looks larger then the left one:
But when we further fade the background to the point where it almost become invisible, and even more important – if we completely cut the pointing arrow heads, the results are outstanding. Not only did we get the solution we thought we would (resulting with both lines becoming equal), surprisingly we find out that the left arrow was in fact lengthier than the ingoing corner’s one!