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An illusion due to Franz Joseph Delboeuf, a Belgian philosopher and expert on hypnosis. If the same circle is placed inside two different concentric circles, its size will ...

The illusion in view by staring at the small black dot for a half minute or so, then switching to the white dot. The black squares appear stationary when staring at the white ...

Three impossible ways to combine four bars.

An impossible figure that locally (but only locally!) looks like a torus.

The illusion illustrated above in which the bounding rectangle and inner square both appear distorted.

In the above figure, the sides a and b have the same length, appearances to the contrary. In the related illusion illustrated above, the interior lines appear to be of ...

The upper horizontal line segment in the above figure appears to be longer than the lower line segment despite the fact that both are the same length.

In the illusion illustrated above, when the concentric square borders with rounded edges are rotated slowly, the entire pattern appears to pulsate radially.

The horizontal line segment in the above figure appears to be shorter than the vertical line segment, despite the fact that it has the same length.

The Schroeder stairs, also called Schouten's staircase (Bool et al. 1982, p. 147), are an ambiguous figure that depicts two different staircases at the same time: one going ...