Schroeder stairs

Schroeder stairs (Schröder's stairs) is an optical illusion which is a two-dimensional drawing which may be perceived either as a drawing of a staircase leading from left to right downwards or the same staircase only turned upside down, a classical example of perspective reversal in psychology of perception.

It is named after the German natural scientist Heinrich G. F. Schröder, who published it in 1858.

The second refers to the phenomenon that after some time of staring at the figure the perception of its orientation becomes involuntarily reversed.

In particular, in one study it was established that involuntary switch of perception occurs with approximate frequency of once in 7.5-12.5 seconds.

[6] The change of perception may be attributed either to neuronal fatigue or to conscious selection.