Understanding touch selection accuracy on flat and hemispherical deformable surfaces

Touch technology is rapidly evolving, and soon deformable, movable and malleable touch interfaces may be part of everyday computing. While there has been a lot of work on understanding touch interactions on flat surfaces, as well as recent work about pointing on curved surfaces, little is known about how surface deformation affects touch interactions. This paper presents the study of how different features of deformable surfaces affect touch selection accuracy, both in terms of position and control of the deformation distance, which refers to the distance traveled by the finger when deforming the surface. We conducted three separate user studies, investigating how touch interactions on a deformable surface are affected not only by the compliant force feedback generated by the elastic surface, but also by the use of visual feedback, the use of a tactile delimiter to indicate the maximum deformation distance, and the use of hemispherical surface shape. The results indicate that, when provided with visual feedback, users can achieve sub-millimeter precision for deformation distance. In addition, without visual feedback, users tend to overestimate deformation distance especially in conditions that require less deformation and therefore provide less surface tension. While the use of a tactile delimiter to indicate maximum deformation improves the distance estimation accuracy, it does not eliminate overestimation. Finally, the shape of the surface also affects touch selection accuracy for both touch position and deformation distance.