In Psychophysical, the law of Weber-Fechner seeks to describe the relation of the Sensation with the physical size of a Stimulus. According to this law, the perceived feeling answers the following formula:

$S\; =\; K\; \backslash \; times\; log\; (I)$

where $S$ is the perceived feeling, $I$ the intensity of stimulation, $k$ a constant and $log$ is the function Logarithme.

Ernst Weber (1795-1878) was one of the first quantitatively to approach the study of the bond between Sensation and physical stimulus and it is in homage to its work which the doctor Gustav Fechner (1801-1887) gave the name of Weber to the quantitative relation that he had discovered. Their successors will keep however the two names to indicate the formula above.

While being based on work of Weber of which he thought that they could provide the base of a possible theorization of the relation spirit-matter, Fechner stated its famous law according to which “ the feeling varies like the logarithm of the excitation ”. However, the experimental checking of this law could be done only thanks to the introduction, about 1860, of the concept of differential Seuil whose quantification rested on new experimental methods. Indeed, according to this law, the fraction of Weber is supposed being constant:

$\backslash \; frac\; \{\backslash \; Delta\; I\}\; \{I\}\; =\; K$

where $\backslash \; Delta\; I$ is the differential threshold (SD) is the smallest difference in perceived intensity, $I$ is the intensity of the stimulus standard and K the constant characteristic of the sensory method in question. The value $\backslash \; Delta\; I/I$ is also called relative differential threshold or Rapport of Bouguer-Weber .

For example, if I can make the difference between an object has weighing 1 kg and another object B weighing 1,2 kg, then my differential threshold is lower than 0,2 kg. While choosing objects B of weights increasingly closer to 1 kg, it arrives one moment when I cannot make the difference between the object any more has and the object B. For example, if B weighs less than 1,1 kg I cannot more distinguish it from has who weigh, then one says that my differential threshold of 0,1 kg for 1 kg, i.e. 10 %. The law of Weber-Fechner stipulates that my relative differential threshold is constant. Thus I would have as much difficulty of distinguishing two objects weighing 1 kg and 1,1 kg that two objects weighing 10 and 11 kg.

It would be more correct of speaking simply about function of Fechner rather than of law , to rather mark the descriptive character than prescriptive (normative) of these functions. Indeed, it proves that this function in fact is not always checked. It is particularly the case when the range of intensity is broad: to the extremes one regularly observes deviations of the law of Weber-Fechner .

This measurement gives an account of a truth felt and thus expressed: time passes more and more quickly, especially towards the end.

Distance of the sum of the causes and the transformations linear and closely connected getting the result, the effect, was made possible only when Fechner had introduced about 1860 the concept of threshold of feeling and had specified certain methods of investigation and observation which made it possible to quantify them.

References

• Bonnet C. (1986) Manual practices the psychophysical one. Armand Collin.
• Fechner G.T. (1860). Element der Psychophysik, Leipzig, Breitskopf and Härtel.

See too

Related articles

• Psychophysical
• Perception
• Feeling
• experimental Psychology

Simple: Weber-Fechner law