Figure 1.

Stimulation protocol and example rasters. a, Stimulation protocol, which stimulated a single distal finger pad with an indented oriented bar. We refer to this as protocol 2. For each stimulus presentation (see Materials and Methods), the bar was rotated to one of eight orientations (22.5° increments) and indented into the skin at one of nine positions per orientation. The center position of the nine positions per orientation was centered within the finger pad, and the other four positions on either side were spaced in 1 mm increments orthogonal to their orientation. b, Example raster (bottom right), position plots (left), and orientation tuning plots (top) for neuron CJ02O_8 that exhibited a divergent vector field that could be explained as a spot of excitation on the distal pad. In the raster, the data are sorted by the eight orientations and nine positions. In the position plots, each curve represents the mean firing rates of one orientation for the nine positions. In the orientation tuning plots, each curve represents the mean firing rates of one position for the eight orientations. c, Example raster, position plots, and orientation tuning plots for neuron CJ001_11 that exhibited an invariant vector field and thereby showed position invariant tuning throughout the distal pad. s/s, Spikes per second.