Abstract
The square–diamond illusion is often referred to as a type of size illusion. However, the 45-degree tilting of a square remarkably affects perceived corner angles when a cube version of the figure is used. This illusion is measured and discussed in relation to anisotropy in shape interpretation.
Highlights
The square–diamond illusion is often referred to as a type of size illusion
The square and the diamond are geometrically congruent, but not recognized as such (Mach, 1897). This square–diamond illusion is essentially a shape illusion but has been referred to as a size illusion
The perceived angles were significantly smaller than 90 degrees for corners L’ (p 1⁄4 .0083), T’ (p 1⁄4 .0022), R’ (p 1⁄4 .0044), and B’ (p 1⁄4 .0911)
Summary
The square–diamond illusion is often referred to as a type of size illusion. the 45-degree tilting of a square remarkably affects perceived corner angles when a cube version of the figure is used. A square is perceived as a diamond when tilted at 45 degrees as shown in Figures 1A and B (Schumann, 1900). This square–diamond illusion is essentially a shape illusion but has been referred to as a size illusion (i.e., the perceived diamond seems bigger than the square).
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