The difference threshold, also known as the just noticeable difference (JND), refers to the smallest change in a stimulus that can be detected by a person. This concept is important in psychology and sensory perception, as it helps to understand how we perceive changes in our environment. For example, if you are holding a weight, the difference threshold determines how much additional weight you need to feel a difference. The difference threshold varies depending on the type of stimulus and the individual's sensitivity. According to Ernst Weber, a German psychologist, this threshold can be expressed as a percentage of the original stimulus. For instance, if you are listening to music, a small increase in volume may be noticeable, while a larger increase might be required to detect a change in brightness when adjusting a light.