Perceptual characteristic of multi-spectral vibrations beyond the human perceivable frequency range

In this paper, we show experimental results indicating that tactile mechanoreceptors have non-linear sensitivity to an applied vibration. We focus on the perceptual characteristic of high frequency amplitude-modulated (AM) vibration. It is known that humans can feel AM vibration even when its carrier frequency is higher than the perceivable range. Non-linearity of perception should be taken into consideration for explaining this characteristic. We observed a deformation of the skin when the AM vibration is applied. We found that we can detect an envelope of the applied AM vibration, even when the skin surface deforms as a linear elastic body; whereas harmonic vibratory pairs cannot be perceived. This result indicates that only a squared value of a displacement, which is proportional to strain energy density, cannot explain the non-linearity of mechanoreceptors. These perceptual characteristics should be taken into consideration for designing a tactile display with multi-spectral vibrations. Otherwise, the simultaneous multi-spectral vibrations can affect each other and may change perceptions because of the non-linearity of the perceptual process.