Measuring the Distribution of Tactile Acuity at the Index Finger and Thumb Fingertips

In our day-to-day activities, we utilize not only the pads of our fingers but also the sides and hemispherical tips when manipulating objects. For teleoperation systems to replicate these real-life interactions, tactile sensation must be presented and distributed across the entire fingertip. Thus, understanding the distribution of tactile acuity at the fingertip is imperative. Although there is a general conception that the tactile acuity of the finger differs between the end of the finger and the finger pad, both the change in resolution and the resolution along the side of the finger are relatively unexplored. We measured the tactile acuity distribution across the entire fingertip of the index finger and thumb, defining it as the ability to distinguish between two discrete orientations of the short linear tip of an indenter. The results revealed that tactile acuity decreased gradually and almost monotonically from fingertip to finger pad, with a significant drop observed at the lateral side of the fingertip. This study provides a fundamental basis for designing devices that can provide a level of tactile presentation wherein shapes can be recognized upon touch.