Haptic identification of curved surfaces

Abstract

In two experiments, the active haptic identification ofthree-dimensional mathematically welldefined objects is investigated. The objects, quadric surfaces, are defined in terms of the shape index, a quantity describing the shape, and curvedness, a quantity describing overall curvature. Both shape index and curvedness are found to have a significant influence on haptic shape identification. Concave surfaces lead to a larger spread in responses than convex ones. Hyperbolic surfaces show a slight tendency to be identified with more difficulty than elliptic ones. Surfaces with a high curvedness are identified more easily than those with a low curvedness. Results from experiments with constant and with random curvedness are indistinguishable. It is concluded that shape index and curvedness are psychophysically not confounded.Haptic sense is of major importance for the perception of the three-dimensional (3-D) shape of tangible objects. An observer will often actively explore an object by using a combination of optics and haptics. Although the importance of active haptic exploration was recognized already by Katz (1925), Revesz (1938), andGibson (1962), hardly any quantitative psychophysical data on haptic perception exist (see, e.g., Loomis & Lederman, 1986). The aim of our research is to collect a coherent body of quantitative data on haptic shape perception of 3-D, roughly handsized objects by active exploration. This paper addresses the first step toward such a goal: haptic identification of curved surfaces by active exploration with only minor restrictions.Few studies have come close to the objectives of our research. Goodwin, John, and Marceglia (1991) and Goodwin and Wheat (1992) have presented quantitative results of experiments in which the subjects had to discriminate spherically curved surfaces applied to their fingerpads. Because Goodwin and colleagues were interested in the capacity of human observers to discriminate and to judge the scale of objects of constant curvature by using only information from the cutaneous receptors, they avoided active exploration in their experiments. With some justice, they argue that the results of active exploration experiments are almost impossible to interpret in terms of the roles of cutaneous afferents, since it is complicated to separate the sensory and motor effects in such tasks. Notwithstanding such arguments, it is important and interesting to learn more about the human capabilities of actively discriminating or identifying 3-D objects.The authors wish to acknowledge the indispensable help of H. Kolijn in the process of manufacturing the shapes and setting up the haptics laboratory. They also wantto thank C. J. M. Wijgerde for his kind help with the software for the milling machine and A. J. Noest for hisvaluable comments. Correspondence should be addressed to A. M. L. Kappers, Utrecht Biophysics Research Institute, Princetonplein 5, 3584 CC Utrecht, The Netherlands (e-mail: a.kappers@fys.ruu.nl). -Accepted by previous editor, Charles W. Eriksen 53Gibson (1963) use...

A shape recognition benchmark for evaluating usability of a haptic environment

“…How does performance in this environment compare with human performance at recognizing physical objects? Using a superset of the five shapes we selected for our benchmark, Kappers et al [2] found accuracy rates close to 100%. They do not report response times.…”

“…In another study, the same authors used a restricted set of objects which could not be readily distinguished by material properties, producing a shape recognition task [4]. Other researchers have used abstract stimuli for shape recognition tasks [2].…”

“…We began with a class of smooth-flowing threedimensional shapes defined by Koenderink and van Doorn [5] and used in the shape recognition task of Kappers et al [2]. These shapes are constructed from two orthogonal parabolas and are a canonical set in the following sense: Any more complex solid shape can be constructed from a combination of these shapes.…”

Perceiving the width and height of a hand-held object by dynamic touch.

“…Koenderink (1990) sought to ground the understanding of visual shape perception in the principal curvatures defined at a surface point given the essential requirement of a quantification of shape that is independent of perspective (coordinate system) and scale. Consonant with Marr's (1982) proposal, Koenderink (see also Lehky & Sejnowski, 1990) tied the coordinate system for a shape to the shape itself, specifically, to its principal directions or eigenvectors and their magnitudes, the eigenvalues k^ and k min (for applications to haptic touch, see Kappers, Koenderink, & Lichtenegger, 1994;Kappers, Koenderink, & te Pas, 1994).…”

Haptic Discrimination of Doubly Curved Surfaces

“…Recently, we introduced a method to investigate haptic shape identification with the aid of mathematically well-defined objects (Kappers et al 1994). A series of quadric surfaces (including elliptical, hyperbolical, spherical, and cylindrical paraboloids) of varying curvature were used to determine performance in terms of percentage correct identification.…”