The ⊥-Illusion Is Not a T-Illusion

Abstract

Variants of the capital Latin letter T were prepared with the straight strokes replaced by J-, C-, or S-curves, mimicking handwritten Ts. These were used to test the hypothesis that the overestimation of the length of the T’s undivided line, relative to the length of its divided line may be understood as an adaptation to a corresponding letter schema. The illusion was greater for S-curve Ts than for C- and J-curve Ts, suggesting that approximate bilateral mirror symmetry is more important for the illusion to occur than letterness. Despite the illusion, observers were quite sensitive to the different lengths of the Ts’ curves.