Weber's Law, explained.
Weber's law relates a just-noticeable change in stimulus intensity to the starting intensity over some ranges and sensory conditions.
Why it happens
Disk area is proportional to the authored intensity units. Increase the right disk's area above a reference of 20 or 80, record a noticeable-difference judgment, and compare the recorded added-area/reference ratios. No threshold is imposed by the software.
Weber's law relates a just-noticeable change in stimulus intensity to the starting intensity over some ranges and sensory conditions.
Read the result
Compare each reported change with its reference, rather than comparing absolute changes alone. The software records your threshold report without enforcing the law.
A worked example
A difference against small and large references
Increase the right disk from the small reference until you choose to report a noticeable difference and save that report.
Switch to the larger reference, which resets added area, and make another report using the same manual procedure.
Inspect the added-area/reference ratios. Similarity or difference is descriptive here, not a psychophysical estimate or a sensory diagnosis.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Disk area is proportional to the authored intensity units. Increase the right disk's area above a reference of 20 or 80, record a noticeable-difference judgment, and compare the recorded added-area/reference ratios. No threshold is imposed by the software.
Where this idea is useful
A practical use
An identical absolute adjustment can be more noticeable relative to a small reference than a large one.
A common misconception
“The same absolute change should be equally noticeable at any starting intensity.”
Relative scale can matter, but Weber-type proportionality holds only within appropriate conditions and ranges. A demonstration should not impose a universal fraction.
What this explanation leaves out
- Manual, visible adjustment and a known manipulation do not estimate a validated psychophysical threshold. The activity allows repeated self-reports and does not assume equal ratios or generalise area judgments to all senses.
Why compare areas rather than circle radii?
The authored intensity units map to disk area, with radius proportional to its square root. Comparing radii would be a different physical manipulation.
Are you evaluating an absolute change or a change relative to a meaningful reference?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.