As we see, that value turns out to be close to 45 ∘, which lies midway between two extremes of orthogonal and tangential contact with the external surface (0° and 90°, respectively). The observed near constancy of that first contact point angle suggests that this is advantageous for the rat. The distribution of the whisker tips on the shroud surface is sufficiently dense such that any first whisker tip to come into contact with an external object will be at practically the same angle relative to the normal to the surface of that object (this may not be the case for the whiskers bordering the mystacial pad as they may approach the object sidewise the latter may explain the smaller deviation from the mean angle for the whiskers forming the interior domain of the shroud) (see Table 1). Speaking metaphorically, the whiskers on a rat’s cheek together compose the Euler spiral.Įach whisker on the rat’s mystacial pad can be viewed as a constitutive element of its tactile sensory system. We can see that the set of whiskers of a given individual animal, when taken together, tends to occupy an interval of the universal Euler spiral extending from one coiled domain to the other (this is more apparent for individuals that are represented by larger numbers of whiskers in our datasets) ( Fig. In addition, the distribution of the shape parameters σ 0 and σ 1 is presented in the parametric plane in Fig.
We calculate σ 0 and σ 1 for all whiskers, and we draw all the representing intervals of the spiral,, each shifted in the vertical direction according to its whisker index, above the universal spiral ( Fig. Each is characterized by a pair of shape parameters σ 0 and σ 1 specifying the arc length coordinates of the end points of the intervals on the universal spiral. These three Euler spiral intervals were rescaled and placed on their corresponding intervals of the universal Euler spiral ( Fig. 3A, where the Euler spiral approximations are superimposed onto the experimentally measured curves. Three exemplar whiskers A, B, and C are shown in Fig.
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