Influence of Shape Elements on Performance during Haptic Rotation Kathrin Krieger 1 , Alexandra Moringen 1 Astrid M.L. Kappers 2 , and Helge Ritter 1 1 Neuroinformatics, CITEC, University Bielefeld, Germany {kkrieger,abarch}@techfak.uni-bielefeld.de 2 Faculty of Behavioural and Movement Sciences, Department of Human Movement Science, Amsterdam, The Netherlands Abstract. In this work, we investigate how local shape elements of a grasped object affect performance of haptic rotation. Blindfolded partic- ipants were asked to grasp a rotary knob using thumb and index finger and to rotate it 90 degrees counterclockwise around its own axis. The knobs exhibited a suitably distributed “grasp conform” combination of local shape elements (edged, flat or round). We tested all possible sce- narios where both fingers had to grasp one of the three shape elements, resulting in a total of nine experimental conditions. Based on the rotation angle, determined with a novel apparatus named Twister, we evaluated the variable and signed errors. The results imply that a round rotary knob is the hardest to rotate by a correct goal angle, while other local shape elements can benefit the performance. Independent of the experi- mental condition, we found a bias towards rotating too far. Keywords: haptic rotation, rotation accuracy, local shape elements 1 Introduction Humans often perform rotations by touch 3 , to interact with the environment in general and to control devices. To facilitate the manipulation of customer devices, there is a long tradition of non-circular shaped rotary knobs. However, haptic design is usually based on experience and far less on empirical analysis [?]. Our goal is, therefore, to investigate whether local shape elements, located under the finger tips during haptic rotation, deliver orientational cues and influence performance. Research on haptic perception of orientations [5, 15] includes investigations on the oblique effect [4, 6, 7, 8] and on parallelism [10, 11, 13, 16]. The oblique effect describes that vertical or horizontal orientations are better processed by humans than oblique orientations, such as 45 or 135 degrees. In parallelism experiments, participants usually explore the angular orientation of a rod and reproduce it with another one. Results show systematic deviations between the 3 We refer to this rotation performed by touch only, as haptic rotation.