Haptic exploration of spheres: Anatomical regions used for perception

Humans can perceive differences in sphericity or how spherical an object is, of objects in the hand within a certain error margin. The part of the hand used to distinguish a perfect sphere from a distorted one is examined in this paper. Using geometry, texture, and other physical cues, subjects detect differences in sphericity. In this experiment subjects were asked to discern a perfect steel ball bearing from a distorted one without visual cues. During the final discrimination task, subjects were given a pair of spheres coated in ink, staining their hands where they touched the ball bearings. Photographs were taken of the ink-stained hands and analyzed with a grid based on anatomical features. The sections of the hand most commonly used among all subjects were the thumb and the area between the index and middle finger. These regions had an average ink coverage of between 81 and 100 percent, much higher values than the rest of the hand.