Whisking mechanics and active sensing

Abstract

We describe recent advances in quantifying the three-dimensional (3D) geometry and mechanics of whisking. Careful delineation of relevant 3D reference frames reveals important geometric and mechanical distinctions between the localization problem (‘where’ is an object) and the feature extraction problem (‘what’ is an object). Head-centered and resting-whisker reference frames lend themselves to quantifying temporal and kinematic cues used for object localization. The whisking-centered reference frame lends itself to quantifying the contact mechanics likely associated with feature extraction. We offer the ‘windowed sampling’ hypothesis for active sensing: that rats can estimate an object’s spatial features by integrating mechanical information across whiskers during brief (25–60 ms) windows of ‘haptic enclosure’ with the whiskers, a motion that resembles a hand grasp.

Behavioral Analysis of Substrate Texture Preference in a Leech,Helobdella austinensis

“…The head movements that H. austinensis uses to determine a favorable substrate surface is similar to the "scanning" movements used by medicinal leeches ( Hirudo verbana ) to locate their prey (Harley and Wagenaar 2014). Many other animals use body extensions such as whiskers and antennae to probe their near-field environment using mechanosensors to determine whether they are about to run into an object (Harley and Ritzmann 2009), to cross over a hole in the ground (Blaesing and Cruse 2004), or even to determine what the object is (rat whisking, Bush et al, 2016). In fact, in a darkened room-especially an unfamiliar one--people use the same sorts of scanning movements with their arms and legs to avoid running into walls, doors, and furniture.…”

Three-dimensional contact point determination and contour reconstruction during active whisking behavior of the awake rat

“…When a rat whisks against an object, as depicted in Figure 1A, the contact point between the whisker and the object is denoted by the coordinates (r wobj , θ wobj , φ wobj ) relative to the whisker basepoint, where the subscript “wobj” stands for whisker-object [25]. The whisker’s deflection causes reaction forces and moments (torques) at the whisker base, denoted as F x , F Y , F Z , M x , M Y , and M Z .…”

“…For each frame of video, we used the tracked 3D shape of the whisker and the tracked location of the 3D whisker-object contact point to compute the mechanical signals F X , M B , and M D at the whisker base. These mechanical signals, shown in Figure 4B, represent the information we assume the rat has during whisking behavior [25, 27, 28]. Details for finding the 3D whisker shape and contact point location are provided in Supplementary Figure 2.…”

“…The mechanoreceptors transduce these deformations to electrical signals, which are transmitted to primary sensory neurons in the trigeminal ganglion (Vg). For an animal to then localize an object in head-centered coordinates, more central levels of the trigeminal pathway would need to integrate information about the whisker’s position and orientation on the face [12, 17, 18, 25]. Alternatively, a recent study suggests that the mapping between mechanical signals in whisker-centered coordinates and the location of an object in head-centered coordinates may also be unique [52].…”

Spatial integration during active tactile sensation drives elementary shape perception

“…The rodent vibrissal system is a powerful model for active sensation and tactile perception, and the mouse offers the genetic tools that make dissecting the cellular and circuit basis of tactile perception possible (Petersen, 2019). Much as primates use their hands, rodents sweep their whiskers across objects to localize and identify them (Diamond et al, 2008)(Bush et al, 2016). Judging object location and shape requires sensory circuits to integrate ex-afferent signals due to whisker contact and re-afferent signals due to self-generated whisker motion, conceptually analogous to proprioceptive input from the hand.…”