Vibration-based rendering of virtual hardness: Frequency characteristics of perception

Humans can distinguish between objects of different hardness by tapping on their surfaces. The frequency and amplitude of the damped natural vibration caused by tapping are known to be cues for the perception of hardness. However, the relationship between them has yet to be entirely understood. We performed a psychophysical experiment using the method of adjustment, wherein participants adjusted the amplitude of stimuli having different frequencies to the point where they felt equally hard. The results could be interpreted as the frequency characteristics of the hardness perception. The amplitude and frequency of the vibration were found to have complementary roles in controlling the perception of hardness.