limen

The point at which a stimulus is strong enough to produce a physiological or psychological response.

In experimental psychology and psychophysics, the threshold; the dividing line between noticeableness and unnoticeableness of stimulus.

In anatomy, the portion of brain-substance situated between the base and the island of Reil.

a threshhold, especially the point where a psychological or physiological effect begins to occur.

the smallest detectable sensation