The mutability of time and space on the skin

Radical shifts in perceived spatial relations can occur through the operation of the principle of sensory saltation. In the realm of cutaneous sensation, where it was first encountered, and also in some auditory and visual situations, any brief stimulus preceding a second one by no more than about 300 ms will show apparent spatial displacement from its veridical position. The degree of deviation is determined primarily by temporal relations between the two stimuli but, secondarily, by intensive ones as well. Limits of the operation of the saltatory effect on the skin have been ascertained by employing a campimetric technique on representative body areas. From the results of such measurement, taken together with consideration of some aspects of the known neural substrate, it is possible to decide among several competing hypotheses concerning the essential seat of the phenomenon. The relation of the saltatory effect to the earlier tau and kappa effects is discussed, as are the possibilities offered by all three to the solution of tactual communication problems and the allied problem of tactile displays.