Computational Geometry in the Human Brain - Discrete and Computational Geometry and Graphs - page 146

Fig. 1. Zollner illusion.

According to this mathematical model, we can strengthen other types of
slanted-line illusions, such as the Cafe Wall illusion [ 11 ] shown in Fig. 2 .In
this figure, in each row, white and black rectangles alternate in the horizontal
direction, and each row is offset from the adjacent rows by half the width of
the rectangles. Although the lines between the rows are straight and horizontal,
they appear to be curved and sloped. This illusion can also be explained by the
Fermuller model [ 9 ].

Fig. 2. Cafe Wall illusion.

Now, since we know that acute angles will be perceived to be larger than
they are, we can expect that this illusion will become stronger if we distort the
rectangles into parallelopipeds, since this will generate a series of acute angles.
The parallelopiped-based Cafe Wall pattern is shown in Fig. 3 . We can observe
that the illusion is stronger, as was predicted by the mathematical model.
These observations, together with the mathematical model, tell us that human
visual perception is affected by blurring, even though we feel that we see the figures
accurately. We can summarize this observation in the following way.

Observation 1. The computations in the human brain are imprecise.