Effect of Material Viscosity on Tactile Compliance Discrimination

The softness perception is a vital yet complex sensory mechanism that we employ in fine manipulative tasks. Although softness perception is typically linked to kinesthetic feedback, in manipulating objects that are comparable to or softer than the skin, tactile feedback plays a crucial role. Lately, beyond contact area and force distribution, temporal cues have been identified as contributors to compliance discrimination. We also previously demonstrated that these human-inspired temporal cues can enable robot sensing softness with a reduced number of sensors in our previous study. However, it remains unclear whether these temporal cues are linked to skin biomechanics, contact dynamics, or material non-linearity. In this study, we examine the impact of material viscosity on tactile softness discrimination. To achieve this, we utilized a viscoelastic springpot model to create a control group of elastic samples and an experimental group of viscoelastic samples. Through a psychophysical experiment, we discovered that viscosity plays a positive role in influencing the discrimination of material softness. This enhanced discrimination may be attributed to asynchronous force rates in the loading and unloading phases of deformation.