(A) Schematic of the kinematic variables of contact. The shape and position of the whisker when at rest is in gray. The variable r indicates the straight-line distance from the basepoint to the contact point. During passive deflections, the relevant angle is , the angle between the line segment that connects the basepoint to the current point of contact and the line segment that connects the basepoint to the initial contact point. The velocity , not shown, is the temporal derivative of . (B) Schematic of the mechanical variables of contact: bending moment (), and the transverse () and axial () components of the applied force (). All variables are computed at the whisker base. (C) Examples of mechanical and kinematic variables during six manually delivered passive deflections in the anesthetized rat. Shading denotes contact episodes. The stimulations are similar but not identical to each other; this imparts a naturalistic variability to the tactile inputs. Units for and are μN; is in μN-m; is in mm; is in degrees; and is in degrees/s. (D) In the awake rat, is no longer well defined, and the relevant angle is , the angle swept out by the tangent to the whisker at its base as the whisker deflects against an object. The velocity is the temporal derivative of . The figure illustrates that , the angle between the tangent to the whisker at its base and the midsagittal plane, is not a valid kinematic variable to explain neural responses because it varies independently of contact.