What You Probably Didn't Know About Humans' Sense Of Smell

So here's a not-too-uncommon scenario: You're in a crowded room, maybe a bar or a restaurant, chatting with a friend. Or, you're one of several in a silent elevator staring at the numbers light up. And ... poof! You catch a whiff of something rank. Keen to catch the flatulent culprit, your head ticks to the side, or maybe you lean your nose up in order to better survey, or you turn your face away to defend from the stench. What do all those responses have in common? Motion. Reason being? People can detect, in 3D, where a smell is coming from, much like sound. Granted, a human being's sense of smell is much more limited in comparison to a dog, for example. But just as humans have two ears, we have two nostrils, and we smell — are you ready? — in stereo.

This should make sense though, right? The phrase "follow your nose" developed for a reason. And there's a reason folks can home in on the room where the Thanksgiving turkey is cooking. The canals leading from both nostrils are separated by the nasal septum and "sample from nonoverlapping regions in space," as phrased by Neuroscience News. So, nostrils allow for a sense of directionality. But, as a 2020 study by the Chinese Academy of Sciences reveals, odorants not only trigger the olfactory nerve to create "smell," but they unconsciously impact our decision-making in a way that we didn't previously understand.

Before you start crafting any tales about "subconscious odors" and pheromonal attraction, let's dial it back and look at the actual study. 

Graduate student Wu Yuli (get ready, folks) "introduced various levels of binaral concentration disparity to a heading judgment paradigm based on optic flow — a unique type of visual stimulus that captures the pattern of apparent motion of surface elements in a visual scene and induces the illusory feeling of self-movement in stationary observers." After participants were introduced to rose odor (phenylethyl alcohol) and vanilla odor (vanillin), the results showed that "moderate binaral disparity biases recipients' perceived direction of self-motion toward the higher-concentration side in manners reminiscent of stereo vision." Say what, again??

Basically, as Sci News outlines, the 180 participants couldn't say which nostril smelled something more strongly, but still felt themselves moving towards the nostril's direction. This means that people are guided right, left, ahead, behind, etc., by scents even if we can't consciously distinguish the strength of a scent within a nostril. This is because, as the study continues to say, the directionality is based on the ratio of chemical concentrations across the nostrils, not the quantity of chemical concentration per nostril. Nifty, huh? So yes, not only is there a reason why some folks find themselves inexplicably drawn down certain aisles in the supermarket, or why they gravitate towards particular health and beauty products, but now we can say how.