Haptic identification of objects and their depictions

Haptic identification of real objects is superior to that of raised two-dimensional (2-D) depic­ tions. Three explanations of real-object superiority were investigated: contribution of material information, contribution of 3-D shape and size, and greater potential for integration across the fingers. In Experiment 1, subjects, while wearing gloves that gently attenuated material infor­ mation, haptically identified real objects that provided reduced cues to compliance, mass, and part motion. The gloves permitted exploration with free hand movement, a single outstretched finger, or five outstretched fingers. Performance decreased over these three conditions but was superior to identification of pictures of the same objects in all cases, indicating the contribution of 3-D structure and integration across the fingers. Picture performance was also better with five fingers than with one. In Experiment 2, the subjects wore open-fingered gloves, which provided them with material information. Consequently, the effect of type of exploration was substantially reduced but not eliminated. Material compensates somewhat for limited access to object struc­ ture but is not the primary basis for haptic object identification. It has been amply demonstrated that people's ability to identify raised line drawings of common objects, using touch alone, is quite poor (Ikeda & Uchikawa, 1978; Kennedy & Fox, 1977; Lederman, Klatzky, Chataway, & Summers, 1990; Loomis, Klatzky, & Lederman, 1991; Magee & Kennedy, 1980). Subjects may spend several minutes on a single picture, and accuracy is generally be­ low 50%-sometimes well below. This is especially strik­ ing when one considers that haptic identification of real, common objects is both fast and accurate, with modal re­ sponse latency observed to be under 2 sec and accuracy near 100% (Klatzky, Lederman, & Metzger, 1985). The purpose of the present study is to evaluate potential ex­ planations of these differences in performance with real objects and two-dimensional (2-D) depictions. We con­ sider three explanations, which are not meant to be mutu­ ally exclusive. The first account of picture/object differences focuses on a salient aspect of haptic perception-namely, that the