This is a fascinating study on how we make value judgments subliminally and possibly irrationally—when people didn’t know they were detecting an odor, they mistakenly attributed a sense of foulness to people shown to them on a screen. When they did know they were detecting an odor, they didn’t let the odor affect how they judged the people.
When the volunteers didn’t detect the odor at all, they rated faces as significantly more likeable when they smelled the pleasant lemon scent, compared to when they sniffed the unpleasant sweat odor (the difference between lemon and neutral and control scents was not significant). By contrast, the students who were able to detect odors showed no significant difference in likeability ratings, no matter what type of odor they smelled.
So when odors are truly subliminal — when we can’t consciously detect them at all — they do affect our ratings of others. The authors argue that when we are conscious of odors, we attempt to account for them in our value judgments. In this case, viewers recognized that the odor was unrelated to the face they were rating, and could successfully account for that fact. When they weren’t conscious of the odor, then processing probably occurred at a different level.