Pretty much every study? Most of the important psychological studies tend to follow a pattern where scientists tell the participants that they're doing X (e.g. measuring their control of body parts when drunk) while actually measuring a completely different Y (half of the group were given fake, non-alcoholic drinks; the goal of the study was to check how much of drunken behavior comes from you knowing that you drink alcohol).

You can't get good results if your subjects know what you're testing for.

Since those participants did give consent to physically being _in_ a study, that's voluntary.

If social norms within the test population (e.g. graduate students) are that pretty much every study tells participants they are doing X, but they end up doing Y, then people are clearly agreeing (consent, free will, expectation based on norms) that they won't know. The norms are a form of disclosure.

What we have here are invisible, silent experiments that violate precedents and norms, without consent.