Poetry involves both conscious and unconscious processes. During writing, poets sometimes try to bypass consciousness, using drugs and dream. Khubla Khan was said to have emerged straight from the subconscious. Sometimes poets try to make their poems bypass the reader's consciousness. Here I'll look at a few reasons why they do this, the methods used, and their consequences.
A feeling can have a greater impact if its cause is ineffable even though visceral, inexplicable reactions may not be a sign of depth and profundity. Some passages of music make the hairs raise on the back of our necks. Scientists played such music (actually by Pink Floyd) to chickens and discovered that their feathers rose at the same point.
A feeling can have a greater impact if its cause is unknown. If an image is flashed too briefly for the conscious mind to appreciate, it can still influence us, and our rational mind finds it harder to resist its message - which is why subliminal advertising is banned on TV and in cinemas.
Sometimes the social situation obliges us to concoct reasons for feelings even if there are none. Post-hypnotic suggestion might make us want to touch curtains, so we do. If someone asks us why, we might say that we're looking out of the window because we're expecting someone - we'd rather invent reasons than deny our underlying urges. Imagine a situation where under hypnosis some people are told that poem A is much better than poem B. Later, they are asked to discuss the merits of the works. The reasons given may change in the course of the discussion, but the relative evaluation is unchallengable.
So from the poet's viewpoint there can be benefits in trying to bypass readers' conscious faculties. It can be done by
- distracting reason (e.g. overloading it) - T.S. Eliot wrote that "The chief use of the 'meaning' of a poem, in the ordinary sense, may be ... to satisfy one habit of the reader, to keep his mind diverted and quiet, while the poem does its work upon him." ("The Use of Poetry", 1933 )
- "hypnotising" reason using rhythm - ritualistic chanting exploits this
- sending reason to sleep - used by minimalistic works, and less extremely in fuzzy work, as suggested by another experiment where it was found that "impressionistic" emotive images were more effective than clear ones. The scientists suggested that this happens because the emotion-detectors react equally strongly to clear and fuzzy images, whereas feature-detection needs detail. The reaction to the fuzzy images isn't diluted by the conscious mind's desire for clarity.
Is there scope for subliminal messages in poetry? In theory, acrostics could work that way, but in practise I doubt whether they do. However, one definition of "poetic effect" (Sperber and Sperber) suggests that it's produced by an accumulation of many slight (not consciously registered) effects. If one's drawn inexplicably to a poem, it might be worth checking which of the above techniques the poet's used.