Single-shot detection of microscale tactile features

Abstract

Tactile detection of very small features requires relative motion between the fingertip and a surface. The specific movement strategies that people use may be critical to maximize detection ability but little is known about the movement strategies people employ to support such detection. Here, human participants actively scanned a fingertip across a pair of silica wafers to detect which of the two contained a microscale feature (2, 6, and 10 m height and 525 m diameter). We constrained fingertip movement to ensure that participants would always contact the feature and would only contact the feature once. These procedures encouraged participants to use strategies that optimized detection rather than search and thus allowed us to more directly link movement strategies to detection. We also investigated the effects of fingertip movement direction and the finger used on detection. We found that participants were able to consistently detect microscale features as small as 2 m on the basis of a single contact event. The contact forces that participants used were substantially higher than those observed in previous studies focused on tactile search or geometric feature extraction. Scanning speeds were slower than those found during tactile search but faster than those reported during geometric feature extraction. Taken in conjunction with the associations between detection and finger used as well as scan direction, our results suggest that control and consistency of fingertip movement may be a primary consideration for movement strategies that optimize tactile detection.