In ̄uence of shape on haptic curvature perception

Curvature discrimination of hand-sized doubly curved surfaces by means of static touch was investigated. Stimuli consisted of hyperbolical, cylindrical, elliptical and spherical surfaces of various curvatures. In the ®rst experiment subjects had to discriminate the curvature along a speci®ed orientation (the discrimination orientation) of a doubly curved surface from a ̄at surface. The curvature to be discriminated was oriented either along the middle ®nger or across the middle ®nger of the right hand. Independent of the shape of the surface, thresholds were found to be about 1.6 times smaller along the middle ®nger than across the middle ®nger. Discrimination biases were found to be strongly in ̄uenced by the shape of the surface; subjects judged a curvature to be more convex when the perpendicular curvature was convex than when this curvature was concave. With the results of the second experiment it could be ruled out that the in ̄uence of shape on curvature perception was simply due to a systematic error made by the subject regarding the discrimination orientation. Ó 1999 Elsevier Science B.V. All rights reserved. PsycINFO classi®cation: 2320