Fig. 2.

Movement of both the fine-textured surface (A) and the ridged surface (B) induced vibrations in the right index fingertip that increased with increasing surface speed. Accelerations were measured in 1-s time windows during constant surface movement with an accelerometer attached to the fingernail. In contrast to the fine-textured surface, the ridged surface generated vibrations with dominant frequencies, which were reliably shifted toward higher frequencies with increasing speed. Arrows in B mark the dominant frequency for each speed.