Fechner's Elusive Parallel Law

2010 ◽  
Vol 23 (4) ◽  
pp. 335-348
Author(s):  
Helen Ross ◽  
Nicholas Wade
Keyword(s):  
Light Adaptation ◽  
Just Noticeable Difference ◽  
Differential Threshold ◽  
Adaptation Level ◽  
Weber’S Law ◽  
Weight Discrimination ◽  
Sensory Stimuli ◽  
Weber's Law ◽  
Perceived Values ◽  
Test Level

AbstractWeber's Law states that the differential threshold or just-noticeable-difference (jnd) is proportional to the physical intensity of the stimulus. Fechner built up his logarithmic law of sensation intensity from Weber's Law and the assumption that all jnds are subjectively equal. He thought it important that the Parallel Law should also hold. The Parallel Law states that, when perceived stimulus intensity is changed by something other than physical intensity (such as adaptation), Weber's Law continues to hold: discrimination should be unchanged provided the perceived values of the two stimuli change in the same ratio. Fechner claimed that weight discrimination was unaffected by weight adaptation; he was unsure about light adaptation; and he claimed that tactile length discrimination was unaffected by perceived changes caused by the bodily location of the stimulus. Modern research on adaptation for weights and other sensory stimuli shows that changes occur both in perceived intensity and in discrimination. Discrimination between stimuli is usually finest when the adaptation level is appropriate to the test level. There is insufficient evidence concerning the discrimination of tactile length and visual length when perceived length is changed. However, the Parallel Law may be untestable because of the difficulty of obtaining measures in the same experiment both for changes in discrimination and for the ratios of the perceived changes of the stimuli.

The neural basis for violations of Weber’s law in self-motion perception

2021 ◽  
Vol 118 (36) ◽  
pp. e2025061118
Author(s):  
Jerome Carriot ◽  
Kathleen E. Cullen ◽  
Maurice J. Chacron
Keyword(s):  
Discrimination Performance ◽  
Fundamental Principle ◽  
Weber’S Law ◽  
Neural Basis ◽  
Sensory Stimuli ◽  
Weber's Law ◽  
Perceptual Performance ◽  
Improved Performance ◽  
Self Motion ◽  
Neural Variability

A prevailing view is that Weber’s law constitutes a fundamental principle of perception. This widely accepted psychophysical law states that the minimal change in a given stimulus that can be perceived increases proportionally with amplitude and has been observed across systems and species in hundreds of studies. Importantly, however, Weber’s law is actually an oversimplification. Notably, there exist violations of Weber’s law that have been consistently observed across sensory modalities. Specifically, perceptual performance is better than that predicted from Weber’s law for the higher stimulus amplitudes commonly found in natural sensory stimuli. To date, the neural mechanisms mediating such violations of Weber’s law in the form of improved perceptual performance remain unknown. Here, we recorded from vestibular thalamocortical neurons in rhesus monkeys during self-motion stimulation. Strikingly, we found that neural discrimination thresholds initially increased but saturated for higher stimulus amplitudes, thereby causing the improved neural discrimination performance required to explain perception. Theory predicts that stimulus-dependent neural variability and/or response nonlinearities will determine discrimination threshold values. Using computational methods, we thus investigated the mechanisms mediating this improved performance. We found that the structure of neural variability, which initially increased but saturated for higher amplitudes, caused improved discrimination performance rather than response nonlinearities. Taken together, our results reveal the neural basis for violations of Weber’s law and further provide insight as to how variability contributes to the adaptive encoding of natural stimuli with continually varying statistics.

Reconciling Fechner and Stevens: Toward a unified psychophysical law

1989 ◽  
Vol 12 (2) ◽  
pp. 251-267 ◽  
Author(s):  
Lester E. Krueger
Keyword(s):  
Power Function ◽  
Category Scale ◽  
Just Noticeable Difference ◽  
Magnitude Scale ◽  
Weber’S Law ◽  
Weber's Law ◽  
Physical Magnitude ◽  
Subjective Magnitude ◽  
Number Magnitude ◽  
Sensory Processes

AbstractHow does subjective magnitude, S. increase as physical magnitude or intensity, I, increases? Direct ratings (magnitude scales; partition or category scales) can be fitted by the power function, S = aIb, in which S equals I raised to a power or exponent, b, and multiplied by a measure constant, a. The exponent is typically about twice as large for the magnitude scale (Stevens) as for the corresponding partition or category scale, but the higher exponent may be explained by the overly expansive way people use numbers in making magnitude estimations. The partition or category scale and the adjusted (for the use of number) magnitude scale for a given modality or condition generally agree with the neurelectric scale and the summated just noticeable difference (jnd) scale. A unified psychophysical law is proposed in which each jnd has the same subjective magnitude for a given modality or condition, subjective magnitude increases as approximately a power function of physical magnitude with the exponent ranging from near 0 to 1 (compressive function), and subjective magnitude depends primarily on peripheral sensory processes, that is, no nonlinear central transformations occur. An undue reliance on Weber's law blinded Fechner to the fact that the true psychophysical scale is approximately a power function. Rejecting Weber's law, which is not valid, means that we no longer have to choose between letting the summated jnd scale be a logarithmic function (Fechner's law) and introducing a nonlinear central transformation to make it into a power function (Brentano–Ekman-Teghtsoonian's law). Fechner and Stevens erred equally about the true psychophysical power function, whose exponent lies halfway between that of Fechner (an exponent approaching zero) and that of Stevens. To be reconciled, Fechnerians must give up the assumptions that Webers law is valid and that the jnd has the same subjective magnitude across modalities and conditions; Stevensians must give up the assumption that the unadjusted (for the use of number) magnitude scale is a direct measure of subjective magnitude.

scholarly journals Weber’s law is the result of exact temporal accumulation of evidence

2018 ◽  
Author(s):  
Jose L. Pardo-Vazquez ◽  
Juan Castiñeiras ◽  
Mafalda Valente ◽  
Tiago Costa ◽  
Alfonso Renart
Keyword(s):  
Reaction Time ◽  
Broad Class ◽  
Sequential Sampling ◽  
Behavioral Effect ◽  
Just Noticeable Difference ◽  
Weber’S Law ◽  
Discrimination Accuracy ◽  
Weber's Law ◽  
Evidence Accumulation ◽  
Hard Limit

AbstractWeber’s law states that the discriminability between two stimulus intensities depends only on their ratio. Despite its status as the cornerstone of psychophysics, the mecha-nisms underlying Weber’s law are still debated, as no principled way exists to choose between its many proposed alternative explanations. We studied this problem training rats to discriminate the lateralization of sounds of different overall level. We found that the rats’ discrimination accuracy in this task is level-invariant, consistent with Weber’s law. Surprisingly, the shape of the reaction time distributions is also level-invariant, implying that the only behavioral effect of changes in the overall level of the sounds is a uniform scaling of time. Furthermore, we demonstrate that Weber’s law breaks down if the stimulus duration is capped at values shorter than the typical reaction time. Together, these facts suggest that Weber’s law is associated to a process of bounded evidence accumulation. Consistent with this hypothesis, we show that, among a broad class of sequential sampling models, the only robust mechanism consistent with reaction time scale-invariance is based on perfect accumulation of evidence up to a constant bound, Poisson-like statistics, and a power-law encoding of stimulus intensity. Fits of a minimal diffusion model with these characteristics describe the rats performance and reaction time distributions with virtually no error. Various manipulations of motivation were unable to alter the rats’ psychometric function, demonstrating the stability of the just-noticeable-difference and suggesting that, at least under some conditions, the bound for evidence accumulation can set a hard limit on discrimination accuracy. Our results establish the mechanistic foundation of the process of intensity discrimination and clarify the factors that limit the precision of sensory systems.

scholarly journals Infant light adaptation shows Weber's law at photopic illuminances

2001 ◽  
Vol 41 (3) ◽  
pp. 359-373 ◽  
Author(s):  
Tuwani A. Rasengane ◽  
John Palmer ◽  
Davida Y. Teller
Keyword(s):  
Light Adaptation ◽  
Weber’S Law ◽  
Weber's Law

Arm Weight, Adaptation, and Weight Discrimination

1967 ◽  
Vol 24 (3_suppl) ◽  
pp. 1127-1130 ◽  
Author(s):  
R. L. Gregory ◽  
Helen E. Ross
Keyword(s):  
Weber’S Law ◽  
Weight Discrimination ◽  
Weber's Law ◽  
Large Weight

The addition of a large weight to the forearm impairs weight discrimination by an amount which is small by Weber's Law but which could affect skilled tasks. When time is allowed for adaptation to the forearm weight, discrimination with the weight is improved and discrimination without the weight is impaired. Implications for pilots and astronauts under varying g are discussed.

scholarly journals Weber’s Law Applies to the Ants’ Visual Perception

2020 ◽  
Vol 11 (2) ◽  
pp. 36
Author(s):  
Marie-Claire Cammaerts ◽  
Roger Cammaerts
Keyword(s):  
Visual Perception ◽  
Operant Conditioning ◽  
Size Effects ◽  
Experimental Methodology ◽  
Just Noticeable Difference ◽  
Weber’S Law ◽  
Numerical Distance ◽  
Weber's Law

Non-numerical distance and size effects have been previously observed in the ant Myrmica sabuleti. As such effects can be theoretically in line with Weber’s law, we presumed that this law, until now examined in vertebrates, could also apply to ants. Using operant conditioning we trained then tested M. sabuleti workers faced with black circles having fixed diameters of 2, 3 and 4 mm against circles with diameters increasing by 0.5 mm until the ants perceived a difference between the smaller and the larger circles. This just noticeable difference occurred when the larger diameter reached 3.5, 5.5 and 7 mm respectively, what corresponded to a ratio larger/smaller surface of 3.06, 3.36 and 3.06. Owing to the degree of accuracy of the experimental methodology, this ratio is sufficiently constant for being consistent with Weber’s law.

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