beneath a limen

From Wikipedia:
A subliminal message is a signal or message embedded in another medium, designed to pass below the normal limits of perception. These messages are unrecognizable by the conscious mind, but in certain situations can affect the subconscious or deeper mind and later actions or attitudes.

Subliminal techniques have occasionally been used in advertising and propaganda; the purpose, the effectiveness, and the frequency of the application of such techniques is debated.