WeberFechner law

According to the Weber-Fechner law, the smallest discernible change in intensity that can be perceived—known as the just noticeable difference (JND)—is a constant ratio of the original stimulus magnitude. As the original intensity of a stimulus increases, the perceptible change in intensity needs to be larger for it to be noticed. This principle is often presented as a logarithmic function, showing that perception of change tends to slow down logarithmically as stimulus intensity increases.

• A person might notice the addition of a candle in a dark room, but may not notice the addition of the same candle in a well-lit room.
• A person might notice the weight change when holding a light object like a pen if an additional pen is added, but won't perceive a pen's weight addition while carrying a heavy backpack.

While the Weber-Fechner law provides a foundational understanding of human perception, critics argue that it oversimplifies the complexities of sensory perception and may not fully account for the variable nature of human sensitivity in different contexts or across diverse populations. Additionally, it is sometimes difficult to apply in modern contexts where varied sensory inputs do not always follow the logarithmic model.