How does the surface shape of what is touched influence perceived softness? Wang, Sun, and Okamoto found that “When a human strokes the surface of an object with his/her finger, the surface shape influences the perceived softness of the object. . . . When a surface with curvature is felt by sliding a finger over it, it feels softer than a flat surface made of the same material. In contrast, a rugged surface is perceived as harder. This illusion indicates that, in addition to mechanical hardness, humans judge an object’s softness based on its surface shape.” Rugged surfaces were sharp peaks and valleys arranged like a series of mountain ranges.
Hongbo Wang, Qingyu Sun, and Shogo Okamoto. (2024). Surface shape alters perceived material softness. i-Perception, 15(2), 1–4. https://doi.org/10.1177/20416695241245021