According to ethical guidelines, under what condition is it permissible for researchers to temporarily withhold the specific research question to prevent participants from altering their behavior?

A researcher studying the effect of mood on memory performance does not reveal the specific research question to participants before data collection begins. During the informed consent process, the researcher describes all procedures participants will complete, outlines the potential risks and benefits of participating, and explicitly states that certain details about the study's purpose are being temporarily withheld until a later explanation session. This approach to temporarily withholding the research question is ethically permissible.