Just-noticeable difference

In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable at least half the time.^[1] This limen is also known as the difference limen, difference threshold, or least perceptible difference.^[2]

^ Cite error: The named reference weberslaw was invoked but never defined (see the help page).
^ Judd 1931, pp. 72–108.

[weberslaw-1] Cite error: The named reference weberslaw was invoked but never defined (see the help page).

[FOOTNOTEJudd193172–108-2] Judd 1931, pp. 72–108.

[1]

[2]

1.	Circles in the upper row grow in arithmetic progression: each one is larger by 10 units than previous one. They make an impression of growing initially fast and then slower and slower (the difference between 10 and 20 seems larger than between 60 and 70).
2	Circles in the lower row grow in geometric progression: each one is larger by 40% than previous one. They make an impression of growing by the same amount at each step.