When does movement help touch? Interstimulus separation and task difficulty in vibrotactile frequency discrimination

Self-controlled movement is often thought to attenuate tactile perception, yet in some contexts, agency can enhance sensory performance. This study examines how interstimulus spatial separation and task difficulty modulate the effects of movement agency on vibrotactile frequency discrimination. Participants judged which of two vibrations, delivered at two separate workspace locations encountered sequentially during lateral translation, was higher in frequency, either through self-controlled or externally guided translation of a haptic device. Discrimination accuracy improved at larger distances, with significantly lower performance at the shortest separation across all groups. Self-controlled movement enhanced accuracy in both easy and difficult tasks, but impaired performance under intermediate difficulty at large separations. These findings challenge simple models of sensory suppression and highlight how spatial configuration, motor control, and task demands jointly shape tactile decisions.