Psychologists and neuroscientists are fairly skeptical of any grand or sinister claims for the power of subliminal advertising or propaganda, but on the other hand, many of them use the technique as a research tool.
So what’s the absolute speed limit of the brain? What’s the minimum time that a stimulus needs to appear in order to trigger a measurable brain response?
In a new study, Swiss researchers Holger Sperdin and colleagues say that they’ve detected neural activity in response to images presented for just 250 microseconds – that’s 1/4 of a millisecond, or 1/4000-th of a second.
(via Subliminal Perception: Just How Fast Is The Brain? – Neuroskeptic, a Discover Magazine blog)
So your brain could respond to a stimuli even when you are not conscious of the stimuli.