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Just Noticeable Difference

In psychophysics, a just noticeable difference, customarily abbreviated with lowercase letters as jnd, is the smallest difference in a specified modality of sensory input that is detectable by a human being. It is also known as the difference limen or the differential threshold.

Explanation

For many sensory dimensions, the 'jnd' is an increasing function of the base level of input, and the ratio of the two is roughly constant (that is the jnd is a constant proportion/percentage of the reference level). Measured in physical units, we have



where is the original intensity of stimulation, is the addition to it required for the difference to be perceived (the jnd), and k is a constant. This rule was first discovered by Ernst Heinrich Weber, in experiments on the thresholds of perception of lifted weights. A theoretical rationale (not universally accepted) was subsequently provided by Gustav Fechner, so the rule is therefore known either as the Weber Law or as the Weber–Fechner law; the constant k is called the Weber constant. It is true, at least to a good approximation, of many but not all sensory dimensions, for example the brightness of lights, and the intensity and the pitch of sounds. It is not true, however, of the wavelength of light. Stanley Smith Stevens argued that it would hold only for what he called prothetic sensory continua, where change of input takes the form an increase in intensity or something obviously analogous; it would not hold for metathetic continua, where change of input produces a qualitative rather than a quantitative change of the percept.

The jnd is a statistical, rather than an exact quantity: from trial to trial, the difference that a given person notices will vary somewhat, and it is therefore necessary to conduct many trials in order to determine the threshold. The jnd usually reported is the difference that a person notices on 50% of trials. If a different proportion is used, this should be included in the description—for example one might report the value of the "75% jnd".

Modern approaches to psychophysics, for example signal detection theory, imply that the observed jnd, even in this statistical sense, is not an absolute quantity, but will depend on situational and motivational as well as perceptual factors.

It has also been observed for the distribution of weights on a beam balance (see [1]).

See also



Psychophysics is a subdiscipline of psychology dealing with the relationship between physical stimuli and their subjective correlates, or percepts.

History


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Ernst Heinrich Weber (Wittenberg, June 24, 1795 – January 26, 1878) was a German physician who is considered a founder of experimental psychology.

Weber studied medicine at Wittenberg University.
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Gustav Theodor Fechner (April 19, 1801 – November 28, 1887), was a German experimental psychologist. A pioneer in experimental psychology and founder of psychophysics, he inspired many 20th century scientists and philosophers, including the philosopher Professor
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Pitch is the perceived fundamental frequency of a sound. While the actual fundamental frequency can be precisely determined through physical measurement, it may differ from the perceived pitch because of overtones, or partials, in the sound.
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Stanley Smith Stevens (1906-1973) was an American psychologist best known as the founder of Harvard's Psycho-Acoustical Laboratory and credited with the introduction of Stevens' power law.
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Detection theory, or signal detection theory, is a means to quantify the ability to discern between signal and noise. Much of the early work in detection theory was done by radar researchers. [1] Detection theory was used in 1966 by John A. Swets and David M.
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A term often used in neuroscience and experimental research. An absolute threshold is the smallest detectable level of a stimulus. For example, in an experiment on sound detention, researchers may present a sound with varying levels of volume.
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In physiology, psychology, or psychophysics, a limen or a liminal point is a threshold of a physiological or psychological response.

Liminal, as an adjective, means situated at a sensory threshold, hence barely perceptible.
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In logic and mathematics, the minimal negation operator is a multigrade operator where each is a k-ary boolean function defined in such a way that if and only if exactly one of the arguments is 0.
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A psychometric function describes the relationship between a parameter of a physical stimulus and the responses of a person who has to decide about a certain aspect of that stimulus.
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