What is "just-noticeable difference"

n. (psychophysics) the difference between two stimuli that (under properly controlled experimental conditions) is detected as often as it is undetected [syn: jnd]

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. This limen is also known as the difference limen, differential threshold, or least perceptible difference.