Differential threshold
The differential threshold is a theoretical concept of the Psychophysique which defines the limit in lower part of which an individual does not manage any more to differentiate two stimulations. One uses also the expression English E just noticeable difference , shortened in jnd or differential limen , shortened in DLL .
In various fields of the Perception, the differential threshold increases with the basic level of stimulation. According to the Law of Weber-Fechner, the ratio of these two quantities is constant:
where is the intensity of basic stimulation, is the differential threshold, i.e. small increment which makes that a difference is perceptible between stimulation considered and basic stimulation and K are a constant known as fraction of Weber or report/ratio of Bouguer-Weber according to the name of the Astronome French Pierre Bouguer which highlighted the capacity of the eye at to adapt to the Luminosité.
This law is checked in many fields of perception (for example in the perception of the tonal Height, the luminous intensity, etc) but one observes sometimes variations when the explored range is widened. A generalization was proposed by Stanley Stevens in the form of a Loi of power, said Loi of Stevens.
The determination of the differential threshold of an individual (human or animal) rests to a statistical measure of the differential threshold obtained empirically during the multiple tests of an experimental protocol. Indeed, since one seeks via the differential threshold to determine the limit of the capacities of the sensory Système, the answers given by the subject are always entâchées of a certain variability. A criterion usually used to define the differential threshold operationally thus consists in bringing back the limiting value for which the subject east perceives a difference in 50% of the tests, but one sometimes prefers to use the differential threshold with 75% which is the limiting value for which the subject is correct in 75% of the tests.
For the psychophysical one inspired by the Theory of the detection of the signal, the differential threshold is not enough to measure to describe the sensory system because this measurement, catch individually, do not make it possible to distinguish the effects related to the context (for example, the Motivation) of the perceptive capacities themselves. With this intention, it is necessary to pass by the determination of the Courbe ROCK.
See too
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