Classic geometrical illusion 21

Classic geometrical illusion 21

since April 22, 2020

"Amodal shrinkage or the shortening height illusion?"

In the top row, there are five vertical rectangles, all of the same size. However, the central vertical rectangle, which is partially obscured by the horizontal rectangle, appears to have a shorter vertical length. This illusion could be referred to as amodal shrinkage. Yet, even when the vertical rectangle is brought forward, as in the bottom row, they still appear shorter. Since this is a shotening height illusion, could the top row also be considered a height-reduction illusion?

Amodal reduction when the occluding object is short (top row) may resemble a rectangular variant of the outer circle underestimation in the Delboeuf illusion (middle and bottom rows).

"Shortening height illusion"

Red rectangles are the same size as each other, but the height of the middle one appears to be shorter.

Kitaoka, A. (2025). A possibly new geometrical illusion "Shortening height illusion." Poster presentation (P2-14) in the 44th Meeting of the Japanese Psychonomic Soceity, Niigata, Japan, November 30, 2025.