@Anon:
Demand characteristics is only one of the problems this kind of research can encounter.
From the APA’s Ethical Principles of Psychologists and Code of Conduct:
Psychologists do not conduct a study involving deception unless they have determined that the use of deceptive techniques is justified by the study’s significant prospective scientific, educational, or applied value and that effective nondeceptive alternative procedures are not feasible.
So, to trick the subject is possible, but yes, you need to do a debriefing afterwards.
On the ethical issue in psychology research: It is my opinion that even if many of researchers in the past used methods that nowadays we consider unethical, we need to consider that some of those researches were real breakthrough in the study of human mind and behavior.
We can. I know it’s not a real answer, but I think behind your question there’s the assumption that “you can’t really know what’s going on in another human mind”, but really, human minds are complicated, but not so complicated, there are more complicated things, and we study and understand them, so…
