"It’s not just puppy dogs who affectionately sniff to get to know you better—humans do it too, we just aren’t aware that we’re doing it. New research from Northwestern University suggests that humans pick up infinitesimal scents that instantly affect whether or not we like somebody. “We evaluate people every day and make judgments about who we like or don’t like,” explains a post-doctoral fellow, Wen Li. “We may think our judgments are based only on various conscious bits of information, but our senses also may provide subliminal perceptual information that affects our behavior.”
Li was lead author of the study published in the December issue of Psychological Science called “Subliminal Smells Can Guide Social Preferences”. The research found that even minute amounts of odors elicited salient psychological and physiological changes that indicate that humans get much more information from barely perceptible scents than scientists have previously realized.
To test whether subliminal odors alter social preferences, participants were asked to sniff bottles with three different scents: lemon (good), sweat (bad) and ethereal (neutral). The scents ranged from levels that could be consciously smelled to those that bordered on being completely imperceptible. Study participants were informed that an odor would be present in 75 percent of the trials. Most participants were not aware of the barely perceptible odors. After sniffing from each of the bottles, they were shown a face with a neutral expression and asked to evaluate it using one of six different rankings, ranging from extremely likeable to extremely unlikeable.
People who were slightly better than average at figuring out whether the minimal smell was present didn’t seem to be biased by the subliminal scents, but everyone else did seem to like faces more or less depending on the “subliminal” smell they’d just whiffed. “The study suggests that people conscious of the barely noticeable scents were able to discount that sensory information and just evaluate the faces,” Li said. “It only was when smell sneaked in without being noticed that judgments about likeability were biased.”
The conclusions fit with recent studies using visual stimuli that suggest that top-down control mechanisms in the brain can be exerted on unconscious processing even though individuals have no awareness of what is being controlled. “When sensory input is insufficient to provoke a conscious olfactory experience, subliminal processing prevails and biases perception,” Paller said. “But as the awareness of a scent increases, greater executive control in the brain is engaged to counteract unconscious olfaction.” The acute sensitivity of human olfaction tends to be under appreciated. “In general, people tend to be dismissive of human olfaction and discount the role that smell plays in our everyday life,” said Gottfried. “Our study offers direct evidence that human social behavior is under the influence of miniscule amounts of odor, at concentrations too low to be consciously perceived, indicating that the human sense of smell is much keener than commonly thought.” In other words, maybe some nice cologne or perfume is more than just a luxurious holiday gift—it may inadvertently make people like the recipient more. Just remember to go light if you want the subliminal effect."