Ernst Heinrich Weber | Biography

Ernst Heinrich Weber made important discoveries about the sense of touch and invented the idea of the just-noticeable difference between two similar physical stimuli. He founded psychophysics, the branch of psychology that studies the relations between physical stimuli and mental states.

Weber, the third of 13 children, was born June 24, 1795, in Wittenburg, Germany. His father was Michael Weber, a professor of theology. Weber learned Latin in secondary school, and began to study medicine in 1811 at the University of Wittenberg. He received his doctor of medicine degree in 1815, specializing in comparative anatomy. Weber became a lecturer at the University of Leipzig in 1817 and was promoted to professor of anatomy the following year. He remained at the University of Leipzig until his retirement.

Weber made his name studying touch, pain, sight, hearing, taste, and smell. He was one of the first psychologists to experiment. He did not just sit at a desk and speculate about human mental states and perceptions. Instead, he tested human subjects to discover how they actually reacted to physical stimuli, publishing the results of many of his experiments about touch in De Tactu in 1834.

Weber developed the concept of the just-noticeable difference. He had his subjects lift one weight and then another to see if they could detect a difference between the two. If the differences were small, the subjects could not tell the two weights apart. If the differences were large, the subjects noticed them. Weber then searched for the smallest perceivable difference between a standard weight and a different weight. He discovered that the just-noticeable difference was best described as a ratio. For lifting weights, the ratio was one to 40. That is, for any standard unit of 40, subjects would notice a difference if one more unit were added to the weight. This ratio applied if Weber used 20, 40, or 80 ounces. If Weber only added half a unit, subjects would not notice the difference. The one-to-40 ratio applied when subjects lifted a weight using both their muscles and their sense of touch. When Weber only rested the weights on a subject's skin, and the subject could not use his muscles to sense the weight, then the ratio became lower, one to 30. The difference in perception meant that sensitivity to change was sharper if a person used two or more senses.

Weber conducted experiments about just-noticeable differences in vision, pain, auditory pitch, smell, and taste. Subjects noticed differences of one-sixtieth in light intensity, one-thirtieth in pain differences, one-tenth in pitch perception, one-quarter in smell, and one-third in taste. The ratios in all of these senses did not hold up at extremes. Thus, if a weight was too small, a subject would not recognize the difference. At the other extreme, if another candle were added to a well-lit room, the subject would not recognize its difference either.

Weber also tested to see if subjects would recognize when they were being touched by one or two points of an object. Weber would close the legs of a drafting compass until their points were almost together, and then touch them to a blindfolded subject's back or cheek. If the legs of the compass were close together, then the subject would perceive them as one touch. Weber then pulled the legs of the compass further apart and touched them again to the subject's back or cheek, to see at what point the subject would notice two touches rather than one. Using this method, Weber discovered that the human body had different sensitivities to touch. Subjects could tell two touches in less than a twentieth of an inch on their tongues, two touches in half an inch on their cheeks, and two touches in 2 « in on their backs. Weber's results were important decades later when nerve endings in the skin were discovered. Fingertips, which have many nerve endings, make very subtle distinctions, but the human back, which has far fewer nerve endings, makes coarser distinctions.

Weber retired from his university professorship in 1871, and he died in Leipzig, Germany, on January 26, 1878.