During environmental exploration, rats rhythmically whisk their vibrissae along the rostro-caudal axis. Each forward extension of the vibrissa array establishes rapid spatiotemporal contact with an object under investigation. This contact presumably produces equally rapid spatiotemporal patterns of population responses in the vibrissa representation of somatosensory cortex (the posterior medial barrel subfield or PMBSF) reflecting features of a stimulus. We used extracellular mapping to identify object features based on spatiotemporal patterns of evoked potentials. Spatiotemporal modeling of evoked potential patterns accurately reconstructed linear versus curved stimuli and detected orientation changes as small is 5 degrees. Whiskers forming arcs in the PMBSF were essential for this reconstruction, and may represent a fundamental processing module. We propose that the PMBSF may function as a spatial frequency analyzer, with intra-row processing integrating a complementary set of spatial frequencies from the arcs in a single whisk.