Electrocutaneous stimulation II. The estimation of distance between two points

Using a numerical estimation procedure, subjects judged the perceived distance between pairs of brief electrical stimuli presented over different physical distances, on different body regions, and in different spatial orientations. The skin turns out to be anisotropic, with the same physical separation between electrodes appearing greater on the forehead than on the forearm, greater on the forearm than on the abdomen. Perceived distance also depends on the orientation and, to some extent, on the time relation between the two electrical pulses. Under all conditions, the perceived distance between electrical stimuli was “compressed” as compared with visual distance. These results bear on the design of devices that attempt to transmit information by electrical stimulation of the skin.