Haptic perception of viscosity

Abstract

Viscosity is a liquid’s resistance against flow. Using a discrimination experiment, the human ability to distinguish between different viscosities was measured over the range of 200–20,000 mPa.s. Eight blindfolded subjects stirred pairs of different silicone oils using a wooden spatula and had to indicate the “thicker” of the two. The viscosity of the liquids was measured seperately using a rheometer. Weber fractions for discrimination ranged from 0.3 at high viscosities to almost 1 at the lowest viscosity. For the higher viscosities, discrimination could be described as Weber-like, but for the low viscosities, there seemed to be a floor effect for the absolute threshold. The characterisation of the discrimination threshold as a function of viscosity is of fundamental interest in perception research, but also of practical value for designers of haptic devices capable of displaying viscosity.