Fig. 2.

Key variables used to describe 3-dimensional (3D) vibrissa collisions. A: in a 3D collision, there are 3 relevant planes: the plane of the intrinsic curvature of the vibrissa, the plane of rotation, and the plane of the object surface. The plane of the vibrissa is defined by the angle ζ. The plane of rotation is defined as the plane normal to the axis about which the vibrissa rotates. This plane is independent of the angle ζ. Finally, the plane of the object surface is defined as the plane tangent to the object surface at the point of vibrissa contact. The relative angles between the 3 planes dictate how the vibrissa will interact with the object. For the purposes of this study, the plane of the object surface is always perpendicular to the plane of rotation. B: there exists a continuum of vibrissa collision types, categorized broadly as occurring against either the concave forward (CF) or the concave backward (CB) face of the vibrissa. A perfectly CF/CB collision occurs when the intrinsic curvature of the vibrissa remains in the plane of rotation. This study focuses specifically on the 2 extremes of the collision spectrum: perfectly CF and perfectly CB collisions. Note that in this particular figure the plane of rotation happens to be the horizontal plane, but in principle it can be any plane.