Influence of shape on haptic curvature perception

Curvature discrimination of hand-sized doubly curved surfaces by means of s tatic touch was investigated. Stimuli consisted of hyperbolical, cylindrica l, elliptical and spherical surfaces of various curvatures. In the first ex periment subjects had to discriminate the curvature along a specified orien tation (the discrimination orientation) of a doubly curved surface from a f lat surface. The curvature to be discriminated was oriented either along th e middle finger or across the middle finger of the right hand. Independent of the shape of the surface, thresholds were found to be about 1.6 times sm aller along the middle finger than across the middle finger. Discrimination biases were found to be strongly influenced by the shape of the surface; s ubjects judged a curvature to be more convex when the perpendicular curvatu re was convex than when this curvature was concave. With the results of the second experiment it could be ruled out that the influence of shape on cur vature perception was simply due to a systematic error made by the subject regarding the discrimination orientation. (C) 1999 Elsevier Science B.V. Al l rights reserved.