Psychophysics gains a new law of sensory perception that also sheds light on subjective perception

Weber’s law, also called Weber-Fechner law, historically important psychological law quantifying the perception of change in a given stimulus. The law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. It has been shown not to hold for extremes of stimulation. (Weber’s Law)

About 200 years ago, the German physician Ernst Heinrich Weber made a seemingly innocuous observation which led to the birth of the discipline of Psychophysics – the science relating physical stimuli in the world and the sensations they evoke in the mind of a subject. Weber asked subjects to say which of two slightly different weights was heavier. From these experiments , he discovered that the probability that a subject will make the right choice only depends on the ratio between the weights.

For instance, if a subject is correct 75% of the time when comparing a weight of 1 Kg and a weight of 1.1 Kg, then she will also be correct 75% of the time when comparing two weights of 2 and 2.2 Kg – or, in general, any pair of weights where one is 10% heavier than the other. This simple but precise rule opened the door to the quantification of behavior in terms of mathematical ‘laws’. (NEUROSCIENTISTS MAKE MAJOR BREAKTHROUGH IN 200-YEAR-OLD PUZZLE)

We investigated Weber’s law by training rats to discriminate the relative intensity of sounds at the two ears at various absolute levels. These experiments revealed the existence of a psychophysical regularity, which we term time–intensity equivalence in discrimination (TIED), describing how reaction times change as a function of absolute level. (The mechanistic foundation of Weber’s law)

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