Feeling Small: Exploring the tactile perception limits
Lisa Skedung, Martin Arvidsson, Jun Y. Chung, Christopher Stafford, Birgitta Berglund, Mark W. Rutland
The human finger is exquisitely sensitive in distinguishing different materials, but the question remains as to what length scales are capable of being discriminated in active touch? We combine psychophysical approaches with materials science to manufacture and explore a series of patterned surfaces of controlled wavelength, but identical chemistry. They are manufactured by a novel stress-gradient-induced wrinkling and subsequent templating. Wavelengths vary from 300 nm to 90 µm and the amplitudes of the roughness vary from 7 nm to 4.5 µm. When these surfaces are pairwise compared by naïve participants and the results analysed using multidimensional scaling, a two dimensional perceptual map of the tactile space is generated. The psychophysical dimensions so generated are directly linked to physical properties - the finger friction coefficient and the surface wavelength. Finally, the amplitude of the features so discriminated is approximately 10 nm, thus driving the tactile perception limit from micrometres into the realm of nano.