WEBER, ERNST HEINRICH

born June 24, 1795, Wittenberg died Jan. 26, 1878, Leipzig, Ger. German anatomist and physiologist whose fundamental studies of the sense of touch introduced a concept-that of the just-noticeable difference, the smallest difference perceivable between two similar stimuli-that is important to psychology and sensory physiology. The eldest of three brothers, all of whom achieved scientific distinction, Weber was a professor at the University of Leipzig from 1818 until 1871. Though he conducted many anatomical investigations, he is known chiefly for his work on sensory response to weight, temperature, and pressure; he described a number of his experiments in this area in De Tactu (1834; "Concerning Touch"). Weber determined that there was a threshold of sensation that must be passed before an increase in the intensity of any stimulus could be detected; the amount of increase necessary to create sensation was the just-noticeable difference. He further observed that the difference was a ratio of the total intensity of sensation, rather than an absolute figure; thus, a greater weight must be added to a 100-pound load than to a 10-pound load for a man carrying the load to notice the change. Similar observations were made on other senses, including sight and hearing. Weber also described a terminal threshold for all senses, the maximum stimulus beyond which no further sensation could be registered. Weber's findings were elaborated in Der Tastsinn und das Gemeingefhl (1851; "The Sense of Touch and the Common Sensibility"), which was considered by the English psychologist E.B. Titchener to be "the foundation stone of experimental psychology." Weber's empirical observations were expressed mathematically by Gustav Theodor Fechner, who called his formulation Weber's law (q.v.).