A Stiffness Discrimination Experiment Including Analysis of Palpation Forces and Velocities

Abstract

For the four standard stiffness values investigated, 0.25, 0.50, 1.00, and 1.25 N/mm, the resulting average stiffness-discrimination Weber fractions were 0.20, 0.27, 0.26, and 0.30, respectively. The average of the forces applied by the subjects was constant within a single session (with a single standard stiffness value). This average force monotonically increased as the standard stiffness value increased across the sessions. We also found positive correlation between the Weber fraction and the palpation speed in the sessions tested with 1.00 and 1.25 N/mm standard stiffness. This correlation suggested that higher speed is related to lower sensitivity in discrimination of stiffness differences for these two standard stiffness values. Our results are applicable to tasks involving stiffness discrimination between multiple objects.