I recall studies (...unless my recollection is a false memory!) where the subjects didn't know they were in an experiment.
For example in one I remember the researchers got the parents and older adult siblings at a family gathering to start talking about funny things that happened when the kids were growing up. That included a made up story about when they went to one of the younger adult siblings' third grade school play, where something funny happened involving him.
Much later the researchers managed to arrange for that person to end up in a conversation that turned to elementary school plays, and that person on their own brought up their third grade play and the funny incident, and even added details that were not in the story told at the gathering.
When I said the story was made up, I didn't mean that what was made up was that something funny happened to him during the play. In fact his third grade class never had a play, nor did any of his other elementary school classes. Nor he did he attend any class plays from other classes.
For example in one I remember the researchers got the parents and older adult siblings at a family gathering to start talking about funny things that happened when the kids were growing up. That included a made up story about when they went to one of the younger adult siblings' third grade school play, where something funny happened involving him.
Much later the researchers managed to arrange for that person to end up in a conversation that turned to elementary school plays, and that person on their own brought up their third grade play and the funny incident, and even added details that were not in the story told at the gathering.
When I said the story was made up, I didn't mean that what was made up was that something funny happened to him during the play. In fact his third grade class never had a play, nor did any of his other elementary school classes. Nor he did he attend any class plays from other classes.