I’ve heard of sub-liminal of course, but just came across the word limen. New to me! Love getting new words like that.
In physiology, psychology, or psychophysics, a limen or a liminal point is a threshold of a physiological or psychological response.
Liminal, as an adjective, means situated at a sensory threshold, hence barely perceptible.
It is a a challenging word. Noticing my own limen is quite task, to go to the edge of awareness. Edges are always interesting, it is where the isomorphy is evident, where we see a world in a grain of sand.