Correct & Vance Packard was good early researcher in this area too. I was referring to running the video at .25 speed and then you can see the images flashed therein - for example there are two or more times a very sexually explicit photo is presented with “Subscribe” on the pic. There are also pics therein embedded which look to be a mess of dots but you can tell there are patterns embedded therein too.
The first time I saw the Exorcist was in a theatre in Toronto. The movie used semi-subliminal cuts of horror frames that went by faster than you could react while leaving fear behind them. People were reportedly getting sick and reacting badly to film.
Not long after, the producers stripped these cuts out of the movie so what we see today is more campy than the original cut and less entertaining.