In physiology, psychology, or psychophysics, a limen or a liminal point is a  threshold of a physiological or psychological response. It is the boundary of perception. On one side of a limen (or threshold) a stimulus is perceivable, on the other side it is not. See also Just noticeable difference Weber 's law 
In physiology, psychology, or psychophysics, a limen or a liminal point is a sensory threshold of a physiological or psychological response. It is the boundary of perception. On one side of a limen (or threshold) a stimulus is perceivable, on the other side it is not. See also Just noticeable difference (least perceptible difference) Threshold of pain, the boundary where perception becomes pain Weber–Fechner law (Weber 's law )
A
sensory
R
Weber
(least perceptible difference) Threshold of pain, the boundary where perception becomes pain Weber–Fechner law (Weber
A
)