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. 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].
Psychology Wiki Explore. Early in the nineteenth century the German physicist, Ernst Weber, developed a technique for measuring the JND, or differential threshold , for different senses. In determining the IND for weight, for example, he would ask a subject to heft an unmarked weight of, say, grams repeatedly, and then heft other weights until he found one that was just noticeably heavier than the given weight on 75 per cent of the trials.
The experiment was continued with other weights, and he found that if the base weight was , the JND weight was ; and if the base weight was , the JND weight was When he determined the fraction in each case, he made the startling discovery that it was exactly the same in every instance—that is,Weber performed tests on different senses and made the even more astonishing discovery that there was a constant fraction for each of them.
He found, for instance, that if he started with 60 lighted candles, it took one additional candle to make a noticeable difference. If he started with candles; it took two, and so on. This limitation does not greatly diminish its value, since most of our experiences involve stimuli of medium intensity.
These results shed interesting light on our sense experience. They indicate that vision is our most sensitive , and smell and taste our least sensitive modality. Moreover, these sensitivities seem to be roughly proportionate to the importance of the different sense organs, since we depend far more on vision than on taste or smell for survival.
The only result that is surprising is our extremely high kinesthetic sensitivity. Animal studies lend support to the evolutionary hypothesis. Weber fractions obtained from discrimination experiments show that fish are extremely sensitive to tastes, dogs and cats to smell, and bats to high-pitched sounds. In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference JND is the amount something must be changed in order for a difference to be noticeable, or detectable at least half the time absolute threshold.
This limen another word for threshold is also known as the difference limen, differential threshold, or least perceptible difference. Measured in physical units, we have:.
This rule was first discovered by Ernst Heinrich Weber — , an anatomist and physiologist, 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 of 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.
If a different proportion is used, this would be included in the description—for example a study might report the value of the 75 percent JND.
Modern approaches to psychophysics, for example signal detection theory, imply that the observed JND is not an absolute quantity, but will depend on situational and motivational as well as perceptual factors. For example, when a researcher flashes a very dim light, a participant may report seeing it on some trials but not on others. It is easy to differentiate between a one-pound bag of rice and a two-pound bag of rice.
There is a one-pound difference, and one bag is twice as heavy as the other. However, would it be as easy to differentiate between a and a pound bag?
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