Final answer:
Ernst Weber found that the just-noticeable difference in a stimulus is a function of the original stimulus's magnitude, forming the basis of Weber's Law. This means that perception of changes in stimulus intensity is relative, and the just-noticeable change is proportional to the starting intensity of the stimulus.
Step-by-step explanation:
In the nineteenth century, the psychophysicist Ernst Weber discovered that the amount of change necessary for a stimulus to be noticed is systematically related to the intensity of the original stimulus itself, which is now known as Weber's Law.
Weber's Law suggests that the just-noticeable difference (jnd), or the smallest change in stimulus that can be detected, is a constant fraction of the original stimulus. Therefore, if we were to test this theory by gradually increasing the weight someone is holding until they notice the difference, the additional weight required to notice this change would not be a fixed amount but a percentage of the starting weight.