Speed-dependent modulation of tactile edge orientation discrimination

Previous studies investigating edge-orientation discrimination capacity either stimulated an immobilized finger at limited speeds, or did not manipulate movement speed during active exploration. Here, we tested the effect of movement speed on edge-orientation discrimination, including very slow and fast speeds. Participants were instructed to move their finger across two pairs of edges while matching their speed to a visual cue. One edge pair was parallel and the other nonparallel to varying degrees. Participants were asked to identify the nonparallel pair of edges. We report three main findings. First, consistent with previous reports, when they were free to choose their movement speed, participants moved at an average speed of ∼29 mm/s (range: 15-52 mm/s). Second, there was no correlation between a participant's natural speed and their edge orientation discrimination capacity. Third, participants got better at edge orientation discrimination at slower than average speeds (5 mm/s), and worse at higher than average speeds (90 and 180 mm/s). Exploratory analysis suggests that this change in performance was correlated with their relative change in movement speed.NEW & NOTEWORTHY Here, we demonstrate speed-dependent variation in edge-orientation discrimination during active tactile exploration, with improved performance at very slow speeds.