Feedback for subjective question

Question 1: Researchers interviewed a group of people in a specific room. They were told that only their interaction with each other and their point of views on a specific issue are being studied but in fact high frequency sound waves were passed through that room and their effect on human behaviour was being observed. Is it an act of deception. Give reason for your choice.
Do you think it was necessary to deceive the respondent in this experiment?
What can the researcher do after the completion of research to rectify the damage done to the respondents?