On the intrinsic curvature of animal whiskers

Facial vibrissae (whiskers) are thin, tapered, and flexible hair-like structures that are an important source of tactile sensory information for many species of animals. In contrast to insect antennae, whiskers have no sensors along their lengths. Instead, when a whisker touches an object, the resulting deformation is transmitted to mechanoreceptors in a follicle at the whisker base. Previous work has shown that the mechanical signals transmitted along the whisker will depend strongly on the whisker’s geometric parameters, in particular on its taper (how diameter varies with arc length) and on its intrinsic curvature. Although previous studies have largely agreed on how to define taper, multiple approaches have been used to quantify intrinsic curvature. The present work, compares and contrasts different mathematical methods to quantify intrinsic curvature, including polynomial, fractional exponent, elliptical, and Cesàro. Comparisons are performed across ten species of whiskered animals, ranging from rodents to pinnipeds. The fractional exponent model is shown to be a particularly promising approach for distinguishing between whiskers of different species. We conclude with a discussion of the advantages and disadvantages of using the different models for different modeling situations.