# Webber's law, Fechner's law and Stevens' law

### Weber's Law

Weber, in the early 19th century, discovered that for a person lifting weights in an experiment, the just distinguishable additional weight depended [somehow] on [what?]. In other words, if the original weight is $$I$$ and the just distinguishable additional weight is $$\Delta I$$, then [something] is a constant.

### Fechner's Law

Fechner wished to derive a transformation that would transform the physical intensity scale to a "perceptual scale" where units on the perceputal scale corresponded to perceptual changes of the same magnitude.

Fechner started with two assumptions:

• Weber's law was valid.
• A just noticeable difference can be considered a [what?].

### Stevens' law

Stevens showed that many relationships between just noticable differences and physical stimulus changes actually follow a [something] law. Steven's work finds its way into some fundamental aspects of color measurement.