Tactile sensory anisotropy: Weber's contribution

E. A. Essock, W. K. Krebs, and J. R. Prather (1997) found that detection of grid patterns by the fingers was best for longitudinal, then oblique, and, last, horizontal orientations. They suggested that the anisotropy is due t o the number of cortical neurons tuned to a stimulus orientation. The contr ibution of E. H. Weber (1834/1996) deserves mention. He found that the 2-po int threshold on the arm was lower for horizontal than for longitudinal ori entations. He (1852/1965) explained this by elongated "sensory circles"-are as of skin served by single nerve fibers. The elongation followed the axis of the main sensory nerves (longitudinal in the arm). Horizontal acuity was finer because the stimulus interval covered more separate fibers. This acc ount is similar to modern ideas on elongated receptive fields, although the locus is peripheral rather than central.