The Discrimination Threshold on the Palm for Two Successive Rectangular Stimuli

This study investigates tactile spatial resolution on the palm using two successive rectangular stimuli. Whereas classical tactile resolution studies have focused mainly on point or circular stimulation, less is known about how spatial resolution depends on the placement and geometry of rectangular, device-relevant stimuli. We measured the successive two-stimulus discrimination threshold using three rectangular stimulators across five palm areas aligned along the proximal–distal axis. Participants compared a fixed reference stimulus with a variable comparison stimulus, and the minimum separation at which the two stimuli were perceived as occurring at different locations was recorded as the threshold. The overall average threshold across all experimental conditions was approximately 5.2 mm. The threshold varied systematically across palm regions, being smallest around the palmar digital crease and the base of the fingers. In the central palm, threshold differences were more evident for changes in stimulator width than for changes in stimulator length. These results extend tactile spatial resolution research beyond point stimulation and provide design-relevant guidance for palm-based haptic devices.