What principle states that two stimuli must differ by a constant percentage to be perceived as different?

The principle that states two stimuli must differ by a constant percentage to be perceived as different is known as Weber's law. This law indicates that the smallest change in a stimulus that can be detected (the just noticeable difference, or JND) is a constant ratio of the original stimulus intensity. For example, if you are lifting weights, the amount you need to increase the weight to notice a difference will depend on the initial weight. If you're lifting 10 pounds, you might only notice a difference with an additional pound, while with 100 pounds, you would need to add a greater amount (10 pounds) to perceive a difference.

Weber's law emphasizes the relative, proportional nature of perception rather than absolute changes. This means the perception of difference is not solely dependent on the actual change in stimulus magnitude but also heavily influenced by the original level of the stimulus. This law is foundational in understanding sensory perception and how individuals experience changes in stimuli across various sensory modalities.

In contrast, other principles like Fechner's law relate to the relationship between stimulus and perception in a different way, focusing on the psychological experience of intensity rather than the proportionality outlined in Weber's law. Stevens' power law also addresses how we perceive differences in stimuli, but it