Spatial acuity of touch: ubiquitous decline with aging revealed by repeated threshold testing

Spatial acuity of touch, like that of vision, tends to decline eventually in nearly everybody's lifetime. This has been revealed by more thorough than customary testing of individual young and elderly subjects. Three kinds of acuity threshold were assessed repeatedly in the index finger. These measured ability to discriminate tactile (1) gaps (by a refined version of two-point threshold), (2) orientation of lines (across vs. along the finger), and (3) length of lines. These acuities relate to prominent discriminatory features of braille, and have been shown earlier to average about 1% larger per annum over the adult life span from about 20 to 80 years. Although there were reliable differences among the elderly subjects in the present experiment, all of them tested consistently worse than the least acute young adult controls. The customary single brief threshold tests heretofore applied are inadequate to capture this ubiquitous but differential individual deficit in advanced age; however, the average of six 15- to 20-min tests spread over 3 days proved more than adequate. The method of repeated threshold testing--applied earlier to olfactory and gustatory sensitivity, and now to tactile acuity--serves to dispel the notion that incidence of sensory loss with aging is highly idiosyncratic.