Figure 3. Vibrissa Micro-Motions During Active Sensing of a Rough Surface.

A. Single frame from high speed video while a rat swept its vibrissae laterally across the surface. The red lines show the tracked positions of an anterior vibrissa every 3^rd frame (~1 msec period) prior to the underlying frame. Regions where tracks are more densely spaced indicate slower motion (sticking). The small white vertical bar demarcates the border between the rough and smooth surfaces, which were removed by intensity normalization. This example is taken from a Supplemental Movie S2. B. Three examples of vibrissae tracked during simultaneous contact with the rough surface from the same trial as Figure 3A. The panel on the left shows every 3^rd vibrissa track in a region of surface interaction (zero distance is the top left corner of the frame). On the right, the red timeseries is the face-centered angle of motion 5 mm from the face, and the blue line is the simultaneous vibrissa motion through a ‘line scan’ placed ~1 mm from the surface (see Methods; horizontal blue line at left). Time zero is arbitrarily chosen just before any vibrissa made surface contact. Black lines on the tracks on the left indicate the vertical divisions in the timeseries on the right (leftmost black mark indicates the onset of the timeseries). The top two vibrissae were from the left side of the face, the bottom vibrissa from the right. As was typical of rough surface interactions, all three vibrissae demonstrated stick-slip behavior, where the vibrissa decelerated for a sustained period, built tension, and then moved rapidly forward in a ballistic manner, until again decelerating. In many cases, this sudden deceleration following a slip was followed by ringing of the vibrissa, a period of high frequency oscillations (for example, three cycles within 185 to 195 msec in B (top); note the ringing is more pronounced at 5 mm (red) than near the contact point (blue)).