Never heard about this before. But my first thought was: Could it be an effect of attempts of information manipulations, like Subliminal stimuli?

I am not a fan of conspiracy theories, for sure, but it is not so hard to imagine situation, when someone is trying to influence even large groups of people with this. Could it be some totalitarian government or some corporation trying to sell something (I know, it does not sounds like conspiracy theory at all ;-).