Graziano & Raulin
Research Methods (9th edition)
Ernst Heinrich Weber (1795-1878) was a German physiologist, whose research focused on the physiology of sense organs.
Weber determined the concept of the two-point threshold. In studies of the discrimination of two stimulus points on the skin, he determined how far apart the points must be in order for the person to report feeling two, rather than one, point of stimulation. Weber also developed what is considered to be the first quantitative law in psychology--the just noticeable difference (JND). He discovered that in making sensory discriminations, such as judging differences between weights, the accuracy of the judgment depends, not on the absolute value of the weight, but on the relative difference between the weights. He determined that the JND for two weights, for example, is a constant ratio of 1:40. That is, an increase of one gram over a standard 40-gram weight is necessary to produce the JND that the weight is heavier than the standard. However, if the standard weight were 400 grams, then the comparison weight would have to be 410 grams in order to be reliably experienced as heavier than the standard.
Weber also studied whether muscular sensations affected the perception of the JND. He found that there is more sensitivity to weight differences when the person lifts the weights, compared to when the weights are placed in his or her hand. The muscular involvement, reasoned Weber, apparently provides additional sensations that are cues for the weight discrimination. Thus, the responses to physical stimuli, such as the weights he used, are not determined by actual weight, but by the proportional weight differences among them and by the nature of other internal sensations, such as those arising from muscular activity.
Weber’s research on the measurement of sensation was impeccably careful, systematic, and experimental. His work stimulated much of the early experimental psychology, and his methods have served as excellent experimental models right to the present.