The Weber–Fechner laws are two related scientific laws in the field of psychophysics, known as Weber's law and Fechner's law. Both relate to human perception, more specifically the relation between the actual change in a physical stimulus and the perceived change. This includes stimuli to all senses: vision, hearing, taste, touch, and smell.
Ernst Heinrich Weber states that "the minimum increase of stimulus which will produce a perceptible increase of sensation is proportional to the pre-existent stimulus," while Gustav Fechner's law is an inference from Weber's law (with additional assumptions) which states that the intensity of our sensation increases as the logarithm of an increase in energy rather than as rapidly as the increase.<ref>Jeans, James (1968/1937). Science & Music, pp. 222, 224. Dover Publications.</ref>
History and formulation of the lawsEdit
Both Weber's law and Fechner's law were formulated by Gustav Theodor Fechner (1801–1887). They were first published in 1860 in the work Elemente der Psychophysik (Elements of Psychophysics). This publication was the first work ever in this field, and where Fechner coined the term psychophysics to describe the interdisciplinary study of how humans perceive physical magnitudes.<ref name="Fechner1">Template:Cite book</ref> He made the claim that "...psycho-physics is an exact doctrine of the relation of function or dependence between body and soul."Template:Sfn
Weber's lawEdit
Ernst Heinrich Weber (1795–1878) was one of the first persons to approach the study of the human response to a physical stimulus in a quantitative fashion. Fechner was a student of Weber and named his first law in honor of his mentor, since it was Weber who had conducted the experiments needed to formulate the law.<ref>Ross, H.E. and Murray, D. J.(Ed. and Transl.) (1996)E.H.Weber on the tactile senses. 2nd ed. Hove: Erlbaum (UK) Taylor & Francis;</ref>
In sensation and contrast , change is defined as "contrast over time". The sense detect the change, specifically in Weber's law, it detects the relative change - not absolute change. In Weber's law, to notice a change in stimulus (e.g. brightness or weight) , the change must be constant proportion of the original stimulus. Weber's law states that just noticeable difference is proportional to the magnitude of the initial stimulus. The brain is a percentage of change detector. The differential threshold is the smallest difference needed to differentiate two stimuli for each sense has been studied by using similarly methods to signal detection. For instance, holding a object that weighs 1,2,10, and 11lbs. Let another person hold the lightest object (1lb). Now, swap out that object for something double the weight. The person will always respond saying that the second object is heavier than the first. However, it makes it difficult when the difference is a small percentage of the overall weight. For example, holding an object that is 10lb. Next, swap it out and hold the object that is 11lb. It would be difficult for one to tell the difference between the two for which is heavier.This shows the idea that bigger stimuli require a larger difference in order to be noticed. <ref>Sensation and perception. Noba. (n.d.). https://nobaproject.com/textbooks/marjorie-rhodes-new-textbook/modules/sensation-and-perception</ref> This is Weber's Law.
Fechner formulated several versions of the law, all communicating the same idea. One formulation states:
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What this means is that the perceived change in stimuli is inversely proportional to the initial stimuli.
Weber's law also incorporates the just-noticeable difference (JND). Let <math>S</math> be some reference stimulus, and <math>dS_{JND}</math> the smallest change in this stimulus that can be perceived. This means that for any <math>dS<dS_{JND}</math> the stimulus <math>S\pm dS</math> is indistinguishable from <math>S</math>. Weber's law states that <math>dS_{JND}</math> and <math>S</math> are proportional to one another,<math>dS_{JND} = k S</math>, where <math>k> 0</math> is some constant of proportionality.<ref>Template:Cite book</ref>
Weber's law always fails at low intensities, near and below the absolute detection threshold, and often also at high intensities, but may be approximately true across a wide middle range of intensities.<ref name=norris>Template:Cite book</ref>
Weber contrastEdit
Although Weber's law includes a statement of the proportionality of a perceived change to initial stimuli, Weber only refers to this as a rule of thumb regarding human perception. It was Fechner who formulated this statement as a mathematical expression referred to as Weber contrast.<ref name="Fechner1" /><ref name="Fechner2">Template:Cite book</ref><ref>Template:Cite thesis</ref><ref>Template:Cite thesis</ref>
<math display="block"> dp = \alpha \frac{dS}{S} \,\!</math>
where <math>dp</math> is how much the perception changes when the stimulus, <math>S</math>, changes by an amount <math>dS</math>. <math>\alpha>0</math> is another proportionality constant. Plugging in the JND, <math>dS=dS_{JND}</math>, we see the proportionality constant in Weber's law is related to the new constant and the smallest perceptual change, <math>dp_{JND}=\alpha k</math>. If <math>dS<dS_{JND}</math> then Weber's law states that <math>dp=0</math>. In Weber contrast this is not the case, so, though the mathematical relationships look similar, they differ in content.
Weber contrast, when integrated, explains Fechner's law (below). Starting at some base stimulus, <math>S_0</math>, and changing it to <math>S</math>, the total change in perception is <math display="block"> p(S)-p(S_0)=\alpha \int_{S_0}^S \frac{dS'}{S'}=\ln \left(\frac{S}{S_0}\right)^\alpha.</math>
Fechner's lawEdit
Fechner noticed in his own studies that different individuals have different sensitivity to certain stimuli. For example, the ability to perceive differences in light intensity could be related to how good that individual's vision is.<ref name ="Fechner1" /> He also noted that how the human sensitivity to stimuli changes depends on which sense is affected. He used this to formulate another version of Weber's law that he named die Maßformel, the "measurement formula". Fechner's law states that the subjective sensation is proportional to the logarithm of the stimulus intensity. According to this law, human perceptions of sight and sound work as follows: Perceived loudness/brightness is proportional to logarithm of the actual intensity measured with an accurate nonhuman instrument,<ref name ="Fechner2" />
<math display="block"> p = \alpha \ln{\frac{S}{S_0}} . \,\!</math>
The relationship between stimulus and perception is logarithmic. A logarithmic relationship means that if a stimulus varies as a geometric progression (i.e., multiplied by a fixed factor), the corresponding perception is altered in an arithmetic progression (i.e., in additive constant amounts). For example, if a stimulus is tripled in strength (i.e., Template:Nowrap), the corresponding perception may be two times as strong as its original value (i.e., Template:Nowrap). If the stimulus is again tripled in strength (i.e., Template:Nowrap), the corresponding perception will be three times as strong as its original value (i.e., Template:Nowrap). Hence, for multiplications in stimulus strength, the strength of perception only adds. The mathematical derivations of the torques on a simple beam balance produce a description that is strictly compatible with Weber's law.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Since Weber's law fails at low intensity, so does Fechner's law.<ref name=norris/>
An early reference to "Fechner's ... law" was in 1875 by Ludimar Hermann in Elements of Human Physiology.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Types of perceptionEdit
Weber and Fechner conducted research on differences in light intensity and the perceived difference in weight.<ref name="Fechner1" /> Other sense modalities provide only mixed support for either Weber's law or Fechner's law.
Weight perceptionEdit
Weber found that the just noticeable difference (JND) between two weights was approximately proportional to the weights. Thus, if the weight of 105 g can (only just) be distinguished from that of 100 g, the JND (or differential threshold) is 5 g. If the mass is doubled, the differential threshold also doubles to 10 g, so that 210 g can be distinguished from 200 g. In this example, a weight (any weight) seems to have to increase by 5% for someone to be able to reliably detect the increase, and this minimum required fractional increase (of 5/100 of the original weight) is referred to as the "Weber fraction" for detecting changes in weight. Other discrimination tasks, such as detecting changes in brightness, or in tone height (pure tone frequency), or in the length of a line shown on a screen, may have different Weber fractions, but they all obey Weber's law in that observed values need to change by at least some small but constant proportion of the current value to ensure human observers will reliably be able to detect that change.
Fechner did not conduct any experiments on how perceived heaviness increased with the mass of the stimulus. Instead, he assumed that all JNDs are subjectively equal, and argued mathematically that this would produce a logarithmic relation between the stimulus intensity and the sensation. These assumptions have both been questioned.<ref>Heidelberger, M. (2004)Nature from within: Gustav Theodor Fechner and his psychophysical worldview. Transl. C. Klohr. Pittsburgh, US: University of Pittsburgh Press.</ref><ref>Template:Cite journal</ref> Following the work of S. S. Stevens, many researchers came to believe in the 1960s that the Stevens's power law was a more general psychophysical principle than Fechner's logarithmic law.
SoundEdit
Weber's law does not quite hold for loudness. It is a fair approximation for higher intensities, but not for lower amplitudes.<ref>Template:Cite book</ref>
Limitation of Weber's law in the auditory systemEdit
Weber's law does not hold at perception of higher intensities. Intensity discrimination improves at higher intensities. The first demonstration of the phenomena was presented by Riesz in 1928, in Physical Review. This deviation of the Weber's law is known as the "near miss" of the Weber's law. This term was coined by McGill and Goldberg in their paper of 1968 in Perception & Psychophysics. Their study consisted of intensity discrimination in pure tones. Further studies have shown that the near miss is observed in noise stimuli as well. Jesteadt et al. (1977)<ref name="Jesteadt Walt, Wier Craig C., Green David M. 1977 169–77">Template:Cite journal</ref> demonstrated that the near miss holds across all the frequencies, and that the intensity discrimination is not a function of frequency, and that the change in discrimination with level can be represented by a single function across all frequencies: <math>\Delta I / I = 0.463 {(I/I_0)}^{-0.072}</math>.<ref name="Jesteadt Walt, Wier Craig C., Green David M. 1977 169–77"/>
VisionEdit
The eye senses brightness approximately logarithmically over a moderate range and stellar magnitude is measured on a logarithmic scale.<ref name=bhatia> Template:Cite book</ref> This magnitude scale was invented by the ancient Greek astronomer Hipparchus in about 150 B.C. He ranked the stars he could see in terms of their brightness, with 1 representing the brightest down to 6 representing the faintest, though now the scale has been extended beyond these limits; an increase in 5 magnitudes corresponds to a decrease in brightness by a factor of 100.<ref name=bhatia/> Modern researchers have attempted to incorporate such perceptual effects into mathematical models of vision.<ref> Template:Cite journal </ref><ref> Template:Cite journal</ref>
Limitations of Weber's law in visual regularity perceptionEdit
Perception of Glass patterns<ref>Template:Cite journal</ref> and mirror symmetries in the presence of noise follows Weber's law in the middle range of regularity-to-noise ratios (S), but in both outer ranges, sensitivity to variations is disproportionally lower. As Maloney, Mitchison, & Barlow (1987)<ref>Template:Cite journal</ref> showed for Glass patterns, and as van der Helm (2010)<ref>Template:Cite journal</ref> showed for mirror symmetries, perception of these visual regularities in the whole range of regularity-to-noise ratios follows the law p = g/(2+1/S) with parameter g to be estimated using experimental data.
Limitation of Weber's law at low light levelsEdit
For vision, Weber's law implies constancy of luminance contrast. Suppose a target object is set against a background luminance <math>B</math>. In order to be just visible, the target must be brighter or fainter than the background by some small amount <math>\Delta B</math>. The Weber contrast is defined as <math>C=\Delta B / B</math>, and Weber's law says that <math>C</math> should be constant for all <math>B</math>.
Human vision follows Weber's law closely at normal daylight levels (i.e. in the photopic range) but begins to break down at twilight levels (the mesopic range) and is completely inapplicable at low light levels (scotopic vision). This can be seen in data collected by Blackwell<ref>Template:Cite journal</ref> and plotted by Crumey,<ref name="crumey">Template:Cite journal</ref> showing threshold increment Template:Math<math>\Delta B</math> versus background luminance Template:Math<math>B</math> for various targets sizes. At daylight levels, the curves are approximately straight with slope 1, i.e. Template:Math<math>\Delta B</math> = Template:Math<math>B + const.</math>, implying <math>C=\Delta B / B</math> is constant. At the very darkest background levels (<math>B</math> ≲ 10− 5 cd m−2, approximately 25 mag arcsec−2)<ref name="crumey"/> the curves are flat - this is where the only visual perception is the observer's own neural noise ('dark light'). In the intermediate range, a portion can be approximated by the De Vries - Rose law, related to Ricco's law.
Logarithmic coding schemes for neuronsEdit
Lognormal distributionsEdit
Activation of neurons by sensory stimuli in many parts of the brain is by a proportional law: neurons change their spike rate by about 10–30%, when a stimulus (e.g. a natural scene for vision) has been applied. However, as Scheler (2017)<ref>Template:Cite journal</ref> showed, the population distribution of the intrinsic excitability or gain of a neuron is a heavy tail distribution, more precisely a lognormal shape, which is equivalent to a logarithmic coding scheme. Neurons may therefore spike with 5–10 fold different mean rates. Obviously, this increases the dynamic range of a neuronal population, while stimulus-derived changes remain small and linear proportional.
An analysis<ref>Template:Cite journal</ref> of the length of comments in internet discussion boards across several languages shows that comment lengths obey the lognormal distribution with great precision. The authors explain the distribution as a manifestation of the Weber–Fechner law.
Other applicationsEdit
The Weber–Fechner law has been applied in other fields of research than just the human senses.
Numerical cognitionEdit
Psychological studies show that it becomes increasingly difficult to discriminate between two numbers as the difference between them decreases. This is called the distance effect.<ref> Template:Cite journal</ref><ref> Template:Cite journal </ref> This is important in areas of magnitude estimation, such as dealing with large scales and estimating distances. It may also play a role in explaining why consumers neglect to shop around to save a small percentage on a large purchase, but will shop around to save a large percentage on a small purchase which represents a much smaller absolute dollar amount.<ref>Template:Cite news</ref>
PharmacologyEdit
It has been hypothesized that dose-response relationships can follow Weber's Law<ref>Template:Cite journal</ref> which suggests this law – which is often applied at the sensory level – originates from underlying chemoreceptor responses to cellular signaling dose relationships within the body. Dose response can be related to the Hill equation, which is closer to a power law.
Public financeEdit
There is a new branch of the literature on public finance hypothesizing that the Weber–Fechner law can explain the increasing levels of public expenditures in mature democracies. Election after election, voters demand more public goods to be effectively impressed; therefore, politicians try to increase the magnitude of this "signal" of competence – the size and composition of public expenditures – in order to collect more votes.<ref>Template:Cite journal</ref>
EmotionEdit
Preliminary research has found that pleasant emotions adhere to Weber’s Law, with accuracy in judging their intensity decreasing as pleasantness increases. However, this pattern wasn't observed for unpleasant emotions, suggesting a survival-related need for accurately discerning high-intensity negative emotions.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
See alsoEdit
- Human nature
- Level (logarithmic quantity)
- Nervous system
- Ricco's law
- Stevens's power law
- Sone
- Neural coding
ReferencesEdit
<references/>
Sensation and perception. Noba. (n.d.). https://nobaproject.com/textbooks/marjorie-rhodes-new-textbook/modules/sensation-and-perception
Further readingEdit
- Template:Cite book (135 pages)
- Template:Cite book
External linksEdit
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