In psychological research how is informed consent even possible?
Leaving aside the basic problem that research is meant to discover new effects, psychology is a wholly imprecise
science subject and the average person's understanding of it is pretty much zero. As a consequence a researcher is not qualified to either list all the possible effects (on the test subject), nor to quantify the risks of taking part - or any possible benefits, either. Nor is a lab-specimen, sorry: test subject in a position to assess whether the value they get from the experiment is worth whatever might, or might not, happen to them: either as a result or just naturally, from life.
Without that basic level of information, any consent is worth no more than "we'd like to do something to you. It probably won't (physically) hurt, but apart from that we can't make any promises". Which is probably little different from the level of personal protection that FB commits to in the Ts & Cs that nobody ever bothers to read, before they accept.