Psychophysical Effects of Grasping Conditions of a Handheld Device on Vibrotactile Perceptions

Tactile perception varies between individuals and the state of the grasp. To investigate the psychophysical effects on vibrotactile perceptions influenced by grasp type and strength of a handheld device, perceived intensities were tested against various grasp strengths and stimulus levels using 40 and 250 Hz vibrations under power grasp and precision grasp conditions. Grasp strength was measured with a pressure distribution sensor on the cylindrical device capable of presenting vibrations up to approximately 2.0 m/s$^{2}$. The analysis using a physical model supported the measured acceleration characteristics, indicating greater attenuation of low-frequency vibrations due to grasping. The psychophysical experiments indicated that the perceived intensity decreases with grasp strength at 40 Hz vibrations under power grasp, whereas the perceived intensity slightly increases with grasp strength at 250 Hz vibrations under precision grasp. On the other hand, small differences were observed for 40 Hz vibrations during precision grasp and 250 Hz vibrations during power grasp. This highlights the need for compensatory measures in low-frequency vibrations or the use of high-frequency vibrations to achieve consistent vibrotactile feedback in handheld devices across different grasping conditions.